builtin.rs

//! Some lints that are built in to the compiler.
//!
//! These are the built-in lints that are emitted direct in the main
//! compiler code, rather than using their own custom pass. Those
//! lints are all available in `rustc_lint::builtin`.

use crate::{declare_lint, declare_lint_pass, FutureIncompatibilityReason};
use rustc_span::edition::Edition;
use rustc_span::symbol::sym;

declare_lint! {
    /// The `forbidden_lint_groups` lint detects violations of
    /// `forbid` applied to a lint group. Due to a bug in the compiler,
    /// these used to be overlooked entirely. They now generate a warning.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![forbid(warnings)]
    /// #![deny(bad_style)]
    ///
    /// fn main() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Recommended fix
    ///
    /// If your crate is using `#![forbid(warnings)]`,
    /// we recommend that you change to `#![deny(warnings)]`.
    ///
    /// ### Explanation
    ///
    /// Due to a compiler bug, applying `forbid` to lint groups
    /// previously had no effect. The bug is now fixed but instead of
    /// enforcing `forbid` we issue this future-compatibility warning
    /// to avoid breaking existing crates.
    pub FORBIDDEN_LINT_GROUPS,
    Warn,
    "applying forbid to lint-groups",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #81670 <https://github.com/rust-lang/rust/issues/81670>",
    };
}

declare_lint! {
    /// The `ill_formed_attribute_input` lint detects ill-formed attribute
    /// inputs that were previously accepted and used in practice.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #[inline = "this is not valid"]
    /// fn foo() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Previously, inputs for many built-in attributes weren't validated and
    /// nonsensical attribute inputs were accepted. After validation was
    /// added, it was determined that some existing projects made use of these
    /// invalid forms. This is a [future-incompatible] lint to transition this
    /// to a hard error in the future. See [issue #57571] for more details.
    ///
    /// Check the [attribute reference] for details on the valid inputs for
    /// attributes.
    ///
    /// [issue #57571]: https://github.com/rust-lang/rust/issues/57571
    /// [attribute reference]: https://doc.rust-lang.org/nightly/reference/attributes.html
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub ILL_FORMED_ATTRIBUTE_INPUT,
    Deny,
    "ill-formed attribute inputs that were previously accepted and used in practice",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #57571 <https://github.com/rust-lang/rust/issues/57571>",
    };
    crate_level_only
}

declare_lint! {
    /// The `conflicting_repr_hints` lint detects [`repr` attributes] with
    /// conflicting hints.
    ///
    /// [`repr` attributes]: https://doc.rust-lang.org/reference/type-layout.html#representations
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #[repr(u32, u64)]
    /// enum Foo {
    ///     Variant1,
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The compiler incorrectly accepted these conflicting representations in
    /// the past. This is a [future-incompatible] lint to transition this to a
    /// hard error in the future. See [issue #68585] for more details.
    ///
    /// To correct the issue, remove one of the conflicting hints.
    ///
    /// [issue #68585]: https://github.com/rust-lang/rust/issues/68585
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub CONFLICTING_REPR_HINTS,
    Deny,
    "conflicts between `#[repr(..)]` hints that were previously accepted and used in practice",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #68585 <https://github.com/rust-lang/rust/issues/68585>",
    };
}

declare_lint! {
    /// The `meta_variable_misuse` lint detects possible meta-variable misuse
    /// in macro definitions.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(meta_variable_misuse)]
    ///
    /// macro_rules! foo {
    ///     () => {};
    ///     ($( $i:ident = $($j:ident),+ );*) => { $( $( $i = $k; )+ )* };
    /// }
    ///
    /// fn main() {
    ///     foo!();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// There are quite a few different ways a [`macro_rules`] macro can be
    /// improperly defined. Many of these errors were previously only detected
    /// when the macro was expanded or not at all. This lint is an attempt to
    /// catch some of these problems when the macro is *defined*.
    ///
    /// This lint is "allow" by default because it may have false positives
    /// and other issues. See [issue #61053] for more details.
    ///
    /// [`macro_rules`]: https://doc.rust-lang.org/reference/macros-by-example.html
    /// [issue #61053]: https://github.com/rust-lang/rust/issues/61053
    pub META_VARIABLE_MISUSE,
    Allow,
    "possible meta-variable misuse at macro definition"
}

declare_lint! {
    /// The `incomplete_include` lint detects the use of the [`include!`]
    /// macro with a file that contains more than one expression.
    ///
    /// [`include!`]: https://doc.rust-lang.org/std/macro.include.html
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs separate file)
    /// fn main() {
    ///     include!("foo.txt");
    /// }
    /// ```
    ///
    /// where the file `foo.txt` contains:
    ///
    /// ```text
    /// println!("hi!");
    /// ```
    ///
    /// produces:
    ///
    /// ```text
    /// error: include macro expected single expression in source
    ///  --> foo.txt:1:14
    ///   |
    /// 1 | println!("1");
    ///   |              ^
    ///   |
    ///   = note: `#[deny(incomplete_include)]` on by default
    /// ```
    ///
    /// ### Explanation
    ///
    /// The [`include!`] macro is currently only intended to be used to
    /// include a single [expression] or multiple [items]. Historically it
    /// would ignore any contents after the first expression, but that can be
    /// confusing. In the example above, the `println!` expression ends just
    /// before the semicolon, making the semicolon "extra" information that is
    /// ignored. Perhaps even more surprising, if the included file had
    /// multiple print statements, the subsequent ones would be ignored!
    ///
    /// One workaround is to place the contents in braces to create a [block
    /// expression]. Also consider alternatives, like using functions to
    /// encapsulate the expressions, or use [proc-macros].
    ///
    /// This is a lint instead of a hard error because existing projects were
    /// found to hit this error. To be cautious, it is a lint for now. The
    /// future semantics of the `include!` macro are also uncertain, see
    /// [issue #35560].
    ///
    /// [items]: https://doc.rust-lang.org/reference/items.html
    /// [expression]: https://doc.rust-lang.org/reference/expressions.html
    /// [block expression]: https://doc.rust-lang.org/reference/expressions/block-expr.html
    /// [proc-macros]: https://doc.rust-lang.org/reference/procedural-macros.html
    /// [issue #35560]: https://github.com/rust-lang/rust/issues/35560
    pub INCOMPLETE_INCLUDE,
    Deny,
    "trailing content in included file"
}

declare_lint! {
    /// The `arithmetic_overflow` lint detects that an arithmetic operation
    /// will [overflow].
    ///
    /// [overflow]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#overflow
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// 1_i32 << 32;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// It is very likely a mistake to perform an arithmetic operation that
    /// overflows its value. If the compiler is able to detect these kinds of
    /// overflows at compile-time, it will trigger this lint. Consider
    /// adjusting the expression to avoid overflow, or use a data type that
    /// will not overflow.
    pub ARITHMETIC_OVERFLOW,
    Deny,
    "arithmetic operation overflows"
}

declare_lint! {
    /// The `unconditional_panic` lint detects an operation that will cause a
    /// panic at runtime.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// # #![allow(unused)]
    /// let x = 1 / 0;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// This lint detects code that is very likely incorrect because it will
    /// always panic, such as division by zero and out-of-bounds array
    /// accesses. Consider adjusting your code if this is a bug, or using the
    /// `panic!` or `unreachable!` macro instead in case the panic is intended.
    pub UNCONDITIONAL_PANIC,
    Deny,
    "operation will cause a panic at runtime"
}

declare_lint! {
    /// The `unused_imports` lint detects imports that are never used.
    ///
    /// ### Example
    ///
    /// ```rust
    /// use std::collections::HashMap;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused imports may signal a mistake or unfinished code, and clutter
    /// the code, and should be removed. If you intended to re-export the item
    /// to make it available outside of the module, add a visibility modifier
    /// like `pub`.
    pub UNUSED_IMPORTS,
    Warn,
    "imports that are never used"
}

declare_lint! {
    /// The `must_not_suspend` lint guards against values that shouldn't be held across suspend points
    /// (`.await`)
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![feature(must_not_suspend)]
    /// #![warn(must_not_suspend)]
    ///
    /// #[must_not_suspend]
    /// struct SyncThing {}
    ///
    /// async fn yield_now() {}
    ///
    /// pub async fn uhoh() {
    ///     let guard = SyncThing {};
    ///     yield_now().await;
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The `must_not_suspend` lint detects values that are marked with the `#[must_not_suspend]`
    /// attribute being held across suspend points. A "suspend" point is usually a `.await` in an async
    /// function.
    ///
    /// This attribute can be used to mark values that are semantically incorrect across suspends
    /// (like certain types of timers), values that have async alternatives, and values that
    /// regularly cause problems with the `Send`-ness of async fn's returned futures (like
    /// `MutexGuard`'s)
    ///
    pub MUST_NOT_SUSPEND,
    Allow,
    "use of a `#[must_not_suspend]` value across a yield point",
    @feature_gate = rustc_span::symbol::sym::must_not_suspend;
}

declare_lint! {
    /// The `unused_extern_crates` lint guards against `extern crate` items
    /// that are never used.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(unused_extern_crates)]
    /// extern crate proc_macro;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// `extern crate` items that are unused have no effect and should be
    /// removed. Note that there are some cases where specifying an `extern
    /// crate` is desired for the side effect of ensuring the given crate is
    /// linked, even though it is not otherwise directly referenced. The lint
    /// can be silenced by aliasing the crate to an underscore, such as
    /// `extern crate foo as _`. Also note that it is no longer idiomatic to
    /// use `extern crate` in the [2018 edition], as extern crates are now
    /// automatically added in scope.
    ///
    /// This lint is "allow" by default because it can be noisy, and produce
    /// false-positives. If a dependency is being removed from a project, it
    /// is recommended to remove it from the build configuration (such as
    /// `Cargo.toml`) to ensure stale build entries aren't left behind.
    ///
    /// [2018 edition]: https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-clarity.html#no-more-extern-crate
    pub UNUSED_EXTERN_CRATES,
    Allow,
    "extern crates that are never used"
}

declare_lint! {
    /// The `unused_crate_dependencies` lint detects crate dependencies that
    /// are never used.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs extern crate)
    /// #![deny(unused_crate_dependencies)]
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// error: external crate `regex` unused in `lint_example`: remove the dependency or add `use regex as _;`
    ///   |
    /// note: the lint level is defined here
    ///  --> src/lib.rs:1:9
    ///   |
    /// 1 | #![deny(unused_crate_dependencies)]
    ///   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
    /// ```
    ///
    /// ### Explanation
    ///
    /// After removing the code that uses a dependency, this usually also
    /// requires removing the dependency from the build configuration.
    /// However, sometimes that step can be missed, which leads to time wasted
    /// building dependencies that are no longer used. This lint can be
    /// enabled to detect dependencies that are never used (more specifically,
    /// any dependency passed with the `--extern` command-line flag that is
    /// never referenced via [`use`], [`extern crate`], or in any [path]).
    ///
    /// This lint is "allow" by default because it can provide false positives
    /// depending on how the build system is configured. For example, when
    /// using Cargo, a "package" consists of multiple crates (such as a
    /// library and a binary), but the dependencies are defined for the
    /// package as a whole. If there is a dependency that is only used in the
    /// binary, but not the library, then the lint will be incorrectly issued
    /// in the library.
    ///
    /// [path]: https://doc.rust-lang.org/reference/paths.html
    /// [`use`]: https://doc.rust-lang.org/reference/items/use-declarations.html
    /// [`extern crate`]: https://doc.rust-lang.org/reference/items/extern-crates.html
    pub UNUSED_CRATE_DEPENDENCIES,
    Allow,
    "crate dependencies that are never used",
    crate_level_only
}

declare_lint! {
    /// The `unused_qualifications` lint detects unnecessarily qualified
    /// names.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(unused_qualifications)]
    /// mod foo {
    ///     pub fn bar() {}
    /// }
    ///
    /// fn main() {
    ///     use foo::bar;
    ///     foo::bar();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// If an item from another module is already brought into scope, then
    /// there is no need to qualify it in this case. You can call `bar()`
    /// directly, without the `foo::`.
    ///
    /// This lint is "allow" by default because it is somewhat pedantic, and
    /// doesn't indicate an actual problem, but rather a stylistic choice, and
    /// can be noisy when refactoring or moving around code.
    pub UNUSED_QUALIFICATIONS,
    Allow,
    "detects unnecessarily qualified names"
}

declare_lint! {
    /// The `unknown_lints` lint detects unrecognized lint attributes.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![allow(not_a_real_lint)]
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// It is usually a mistake to specify a lint that does not exist. Check
    /// the spelling, and check the lint listing for the correct name. Also
    /// consider if you are using an old version of the compiler, and the lint
    /// is only available in a newer version.
    pub UNKNOWN_LINTS,
    Warn,
    "unrecognized lint attribute"
}

declare_lint! {
    /// The `unfulfilled_lint_expectations` lint detects lint trigger expectations
    /// that have not been fulfilled.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![feature(lint_reasons)]
    ///
    /// #[expect(unused_variables)]
    /// let x = 10;
    /// println!("{}", x);
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// It was expected that the marked code would emit a lint. This expectation
    /// has not been fulfilled.
    ///
    /// The `expect` attribute can be removed if this is intended behavior otherwise
    /// it should be investigated why the expected lint is no longer issued.
    ///
    /// In rare cases, the expectation might be emitted at a different location than
    /// shown in the shown code snippet. In most cases, the `#[expect]` attribute
    /// works when added to the outer scope. A few lints can only be expected
    /// on a crate level.
    ///
    /// Part of RFC 2383. The progress is being tracked in [#54503]
    ///
    /// [#54503]: https://github.com/rust-lang/rust/issues/54503
    pub UNFULFILLED_LINT_EXPECTATIONS,
    Warn,
    "unfulfilled lint expectation",
    @feature_gate = rustc_span::sym::lint_reasons;
}

declare_lint! {
    /// The `unused_variables` lint detects variables which are not used in
    /// any way.
    ///
    /// ### Example
    ///
    /// ```rust
    /// let x = 5;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused variables may signal a mistake or unfinished code. To silence
    /// the warning for the individual variable, prefix it with an underscore
    /// such as `_x`.
    pub UNUSED_VARIABLES,
    Warn,
    "detect variables which are not used in any way"
}

declare_lint! {
    /// The `unused_assignments` lint detects assignments that will never be read.
    ///
    /// ### Example
    ///
    /// ```rust
    /// let mut x = 5;
    /// x = 6;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused assignments may signal a mistake or unfinished code. If the
    /// variable is never used after being assigned, then the assignment can
    /// be removed. Variables with an underscore prefix such as `_x` will not
    /// trigger this lint.
    pub UNUSED_ASSIGNMENTS,
    Warn,
    "detect assignments that will never be read"
}

declare_lint! {
    /// The `dead_code` lint detects unused, unexported items.
    ///
    /// ### Example
    ///
    /// ```rust
    /// fn foo() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Dead code may signal a mistake or unfinished code. To silence the
    /// warning for individual items, prefix the name with an underscore such
    /// as `_foo`. If it was intended to expose the item outside of the crate,
    /// consider adding a visibility modifier like `pub`. Otherwise consider
    /// removing the unused code.
    pub DEAD_CODE,
    Warn,
    "detect unused, unexported items"
}

declare_lint! {
    /// The `unused_attributes` lint detects attributes that were not used by
    /// the compiler.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![ignore]
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused [attributes] may indicate the attribute is placed in the wrong
    /// position. Consider removing it, or placing it in the correct position.
    /// Also consider if you intended to use an _inner attribute_ (with a `!`
    /// such as `#![allow(unused)]`) which applies to the item the attribute
    /// is within, or an _outer attribute_ (without a `!` such as
    /// `#[allow(unused)]`) which applies to the item *following* the
    /// attribute.
    ///
    /// [attributes]: https://doc.rust-lang.org/reference/attributes.html
    pub UNUSED_ATTRIBUTES,
    Warn,
    "detects attributes that were not used by the compiler"
}

declare_lint! {
    /// The `unused_tuple_struct_fields` lint detects fields of tuple structs
    /// that are never read.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #[warn(unused_tuple_struct_fields)]
    /// struct S(i32, i32, i32);
    /// let s = S(1, 2, 3);
    /// let _ = (s.0, s.2);
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Tuple struct fields that are never read anywhere may indicate a
    /// mistake or unfinished code. To silence this warning, consider
    /// removing the unused field(s) or, to preserve the numbering of the
    /// remaining fields, change the unused field(s) to have unit type.
    pub UNUSED_TUPLE_STRUCT_FIELDS,
    Allow,
    "detects tuple struct fields that are never read"
}

declare_lint! {
    /// The `unreachable_code` lint detects unreachable code paths.
    ///
    /// ### Example
    ///
    /// ```rust,no_run
    /// panic!("we never go past here!");
    ///
    /// let x = 5;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unreachable code may signal a mistake or unfinished code. If the code
    /// is no longer in use, consider removing it.
    pub UNREACHABLE_CODE,
    Warn,
    "detects unreachable code paths",
    report_in_external_macro
}

declare_lint! {
    /// The `unreachable_patterns` lint detects unreachable patterns.
    ///
    /// ### Example
    ///
    /// ```rust
    /// let x = 5;
    /// match x {
    ///     y => (),
    ///     5 => (),
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// This usually indicates a mistake in how the patterns are specified or
    /// ordered. In this example, the `y` pattern will always match, so the
    /// five is impossible to reach. Remember, match arms match in order, you
    /// probably wanted to put the `5` case above the `y` case.
    pub UNREACHABLE_PATTERNS,
    Warn,
    "detects unreachable patterns"
}

declare_lint! {
    /// The `overlapping_range_endpoints` lint detects `match` arms that have [range patterns] that
    /// overlap on their endpoints.
    ///
    /// [range patterns]: https://doc.rust-lang.org/nightly/reference/patterns.html#range-patterns
    ///
    /// ### Example
    ///
    /// ```rust
    /// let x = 123u8;
    /// match x {
    ///     0..=100 => { println!("small"); }
    ///     100..=255 => { println!("large"); }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// It is likely a mistake to have range patterns in a match expression that overlap in this
    /// way. Check that the beginning and end values are what you expect, and keep in mind that
    /// with `..=` the left and right bounds are inclusive.
    pub OVERLAPPING_RANGE_ENDPOINTS,
    Warn,
    "detects range patterns with overlapping endpoints"
}

declare_lint! {
    /// The `bindings_with_variant_name` lint detects pattern bindings with
    /// the same name as one of the matched variants.
    ///
    /// ### Example
    ///
    /// ```rust
    /// pub enum Enum {
    ///     Foo,
    ///     Bar,
    /// }
    ///
    /// pub fn foo(x: Enum) {
    ///     match x {
    ///         Foo => {}
    ///         Bar => {}
    ///     }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// It is usually a mistake to specify an enum variant name as an
    /// [identifier pattern]. In the example above, the `match` arms are
    /// specifying a variable name to bind the value of `x` to. The second arm
    /// is ignored because the first one matches *all* values. The likely
    /// intent is that the arm was intended to match on the enum variant.
    ///
    /// Two possible solutions are:
    ///
    /// * Specify the enum variant using a [path pattern], such as
    ///   `Enum::Foo`.
    /// * Bring the enum variants into local scope, such as adding `use
    ///   Enum::*;` to the beginning of the `foo` function in the example
    ///   above.
    ///
    /// [identifier pattern]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
    /// [path pattern]: https://doc.rust-lang.org/reference/patterns.html#path-patterns
    pub BINDINGS_WITH_VARIANT_NAME,
    Warn,
    "detects pattern bindings with the same name as one of the matched variants"
}

declare_lint! {
    /// The `unused_macros` lint detects macros that were not used.
    ///
    /// Note that this lint is distinct from the `unused_macro_rules` lint,
    /// which checks for single rules that never match of an otherwise used
    /// macro, and thus never expand.
    ///
    /// ### Example
    ///
    /// ```rust
    /// macro_rules! unused {
    ///     () => {};
    /// }
    ///
    /// fn main() {
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused macros may signal a mistake or unfinished code. To silence the
    /// warning for the individual macro, prefix the name with an underscore
    /// such as `_my_macro`. If you intended to export the macro to make it
    /// available outside of the crate, use the [`macro_export` attribute].
    ///
    /// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
    pub UNUSED_MACROS,
    Warn,
    "detects macros that were not used"
}

declare_lint! {
    /// The `unused_macro_rules` lint detects macro rules that were not used.
    ///
    /// Note that the lint is distinct from the `unused_macros` lint, which
    /// fires if the entire macro is never called, while this lint fires for
    /// single unused rules of the macro that is otherwise used.
    /// `unused_macro_rules` fires only if `unused_macros` wouldn't fire.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #[warn(unused_macro_rules)]
    /// macro_rules! unused_empty {
    ///     (hello) => { println!("Hello, world!") }; // This rule is unused
    ///     () => { println!("empty") }; // This rule is used
    /// }
    ///
    /// fn main() {
    ///     unused_empty!(hello);
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused macro rules may signal a mistake or unfinished code. Furthermore,
    /// they slow down compilation. Right now, silencing the warning is not
    /// supported on a single rule level, so you have to add an allow to the
    /// entire macro definition.
    ///
    /// If you intended to export the macro to make it
    /// available outside of the crate, use the [`macro_export` attribute].
    ///
    /// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
    pub UNUSED_MACRO_RULES,
    Allow,
    "detects macro rules that were not used"
}

declare_lint! {
    /// The `warnings` lint allows you to change the level of other
    /// lints which produce warnings.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![deny(warnings)]
    /// fn foo() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The `warnings` lint is a bit special; by changing its level, you
    /// change every other warning that would produce a warning to whatever
    /// value you'd like. As such, you won't ever trigger this lint in your
    /// code directly.
    pub WARNINGS,
    Warn,
    "mass-change the level for lints which produce warnings"
}

declare_lint! {
    /// The `unused_features` lint detects unused or unknown features found in
    /// crate-level [`feature` attributes].
    ///
    /// [`feature` attributes]: https://doc.rust-lang.org/nightly/unstable-book/
    ///
    /// Note: This lint is currently not functional, see [issue #44232] for
    /// more details.
    ///
    /// [issue #44232]: https://github.com/rust-lang/rust/issues/44232
    pub UNUSED_FEATURES,
    Warn,
    "unused features found in crate-level `#[feature]` directives"
}

declare_lint! {
    /// The `stable_features` lint detects a [`feature` attribute] that
    /// has since been made stable.
    ///
    /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![feature(test_accepted_feature)]
    /// fn main() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// When a feature is stabilized, it is no longer necessary to include a
    /// `#![feature]` attribute for it. To fix, simply remove the
    /// `#![feature]` attribute.
    pub STABLE_FEATURES,
    Warn,
    "stable features found in `#[feature]` directive"
}

declare_lint! {
    /// The `unknown_crate_types` lint detects an unknown crate type found in
    /// a [`crate_type` attribute].
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![crate_type="lol"]
    /// fn main() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// An unknown value give to the `crate_type` attribute is almost
    /// certainly a mistake.
    ///
    /// [`crate_type` attribute]: https://doc.rust-lang.org/reference/linkage.html
    pub UNKNOWN_CRATE_TYPES,
    Deny,
    "unknown crate type found in `#[crate_type]` directive",
    crate_level_only
}

declare_lint! {
    /// The `trivial_casts` lint detects trivial casts which could be replaced
    /// with coercion, which may require [type ascription] or a temporary
    /// variable.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(trivial_casts)]
    /// let x: &u32 = &42;
    /// let y = x as *const u32;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// A trivial cast is a cast `e as T` where `e` has type `U` and `U` is a
    /// subtype of `T`. This type of cast is usually unnecessary, as it can be
    /// usually be inferred.
    ///
    /// This lint is "allow" by default because there are situations, such as
    /// with FFI interfaces or complex type aliases, where it triggers
    /// incorrectly, or in situations where it will be more difficult to
    /// clearly express the intent. It may be possible that this will become a
    /// warning in the future, possibly with [type ascription] providing a
    /// convenient way to work around the current issues. See [RFC 401] for
    /// historical context.
    ///
    /// [type ascription]: https://github.com/rust-lang/rust/issues/23416
    /// [RFC 401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
    pub TRIVIAL_CASTS,
    Allow,
    "detects trivial casts which could be removed"
}

declare_lint! {
    /// The `trivial_numeric_casts` lint detects trivial numeric casts of types
    /// which could be removed.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(trivial_numeric_casts)]
    /// let x = 42_i32 as i32;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// A trivial numeric cast is a cast of a numeric type to the same numeric
    /// type. This type of cast is usually unnecessary.
    ///
    /// This lint is "allow" by default because there are situations, such as
    /// with FFI interfaces or complex type aliases, where it triggers
    /// incorrectly, or in situations where it will be more difficult to
    /// clearly express the intent. It may be possible that this will become a
    /// warning in the future, possibly with [type ascription] providing a
    /// convenient way to work around the current issues. See [RFC 401] for
    /// historical context.
    ///
    /// [type ascription]: https://github.com/rust-lang/rust/issues/23416
    /// [RFC 401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
    pub TRIVIAL_NUMERIC_CASTS,
    Allow,
    "detects trivial casts of numeric types which could be removed"
}

declare_lint! {
    /// The `private_in_public` lint detects private items in public
    /// interfaces not caught by the old implementation.
    ///
    /// ### Example
    ///
    /// ```rust
    /// # #![allow(unused)]
    /// struct SemiPriv;
    ///
    /// mod m1 {
    ///     struct Priv;
    ///     impl super::SemiPriv {
    ///         pub fn f(_: Priv) {}
    ///     }
    /// }
    /// # fn main() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The visibility rules are intended to prevent exposing private items in
    /// public interfaces. This is a [future-incompatible] lint to transition
    /// this to a hard error in the future. See [issue #34537] for more
    /// details.
    ///
    /// [issue #34537]: https://github.com/rust-lang/rust/issues/34537
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub PRIVATE_IN_PUBLIC,
    Warn,
    "detect private items in public interfaces not caught by the old implementation",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #34537 <https://github.com/rust-lang/rust/issues/34537>",
    };
}

declare_lint! {
    /// The `exported_private_dependencies` lint detects private dependencies
    /// that are exposed in a public interface.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs-dependency)
    /// pub fn foo() -> Option<some_private_dependency::Thing> {
    ///     None
    /// }
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: type `bar::Thing` from private dependency 'bar' in public interface
    ///  --> src/lib.rs:3:1
    ///   |
    /// 3 | pub fn foo() -> Option<bar::Thing> {
    ///   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ///   |
    ///   = note: `#[warn(exported_private_dependencies)]` on by default
    /// ```
    ///
    /// ### Explanation
    ///
    /// Dependencies can be marked as "private" to indicate that they are not
    /// exposed in the public interface of a crate. This can be used by Cargo
    /// to independently resolve those dependencies because it can assume it
    /// does not need to unify them with other packages using that same
    /// dependency. This lint is an indication of a violation of that
    /// contract.
    ///
    /// To fix this, avoid exposing the dependency in your public interface.
    /// Or, switch the dependency to a public dependency.
    ///
    /// Note that support for this is only available on the nightly channel.
    /// See [RFC 1977] for more details, as well as the [Cargo documentation].
    ///
    /// [RFC 1977]: https://github.com/rust-lang/rfcs/blob/master/text/1977-public-private-dependencies.md
    /// [Cargo documentation]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#public-dependency
    pub EXPORTED_PRIVATE_DEPENDENCIES,
    Warn,
    "public interface leaks type from a private dependency"
}

declare_lint! {
    /// The `pub_use_of_private_extern_crate` lint detects a specific
    /// situation of re-exporting a private `extern crate`.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// extern crate core;
    /// pub use core as reexported_core;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// A public `use` declaration should not be used to publicly re-export a
    /// private `extern crate`. `pub extern crate` should be used instead.
    ///
    /// This was historically allowed, but is not the intended behavior
    /// according to the visibility rules. This is a [future-incompatible]
    /// lint to transition this to a hard error in the future. See [issue
    /// #34537] for more details.
    ///
    /// [issue #34537]: https://github.com/rust-lang/rust/issues/34537
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub PUB_USE_OF_PRIVATE_EXTERN_CRATE,
    Deny,
    "detect public re-exports of private extern crates",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #34537 <https://github.com/rust-lang/rust/issues/34537>",
    };
}

declare_lint! {
    /// The `invalid_type_param_default` lint detects type parameter defaults
    /// erroneously allowed in an invalid location.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// fn foo<T=i32>(t: T) {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Default type parameters were only intended to be allowed in certain
    /// situations, but historically the compiler allowed them everywhere.
    /// This is a [future-incompatible] lint to transition this to a hard
    /// error in the future. See [issue #36887] for more details.
    ///
    /// [issue #36887]: https://github.com/rust-lang/rust/issues/36887
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub INVALID_TYPE_PARAM_DEFAULT,
    Deny,
    "type parameter default erroneously allowed in invalid location",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #36887 <https://github.com/rust-lang/rust/issues/36887>",
    };
}

declare_lint! {
    /// The `renamed_and_removed_lints` lint detects lints that have been
    /// renamed or removed.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![deny(raw_pointer_derive)]
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// To fix this, either remove the lint or use the new name. This can help
    /// avoid confusion about lints that are no longer valid, and help
    /// maintain consistency for renamed lints.
    pub RENAMED_AND_REMOVED_LINTS,
    Warn,
    "lints that have been renamed or removed"
}

declare_lint! {
    /// The `unaligned_references` lint detects unaligned references to fields
    /// of [packed] structs.
    ///
    /// [packed]: https://doc.rust-lang.org/reference/type-layout.html#the-alignment-modifiers
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #[repr(packed)]
    /// pub struct Foo {
    ///     field1: u64,
    ///     field2: u8,
    /// }
    ///
    /// fn main() {
    ///     unsafe {
    ///         let foo = Foo { field1: 0, field2: 0 };
    ///         let _ = &foo.field1;
    ///         println!("{}", foo.field1); // An implicit `&` is added here, triggering the lint.
    ///     }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Creating a reference to an insufficiently aligned packed field is [undefined behavior] and
    /// should be disallowed. Using an `unsafe` block does not change anything about this. Instead,
    /// the code should do a copy of the data in the packed field or use raw pointers and unaligned
    /// accesses. See [issue #82523] for more information.
    ///
    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
    /// [issue #82523]: https://github.com/rust-lang/rust/issues/82523
    pub UNALIGNED_REFERENCES,
    Deny,
    "detects unaligned references to fields of packed structs",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #82523 <https://github.com/rust-lang/rust/issues/82523>",
        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
    };
    report_in_external_macro
}

declare_lint! {
    /// The `const_item_mutation` lint detects attempts to mutate a `const`
    /// item.
    ///
    /// ### Example
    ///
    /// ```rust
    /// const FOO: [i32; 1] = [0];
    ///
    /// fn main() {
    ///     FOO[0] = 1;
    ///     // This will print "[0]".
    ///     println!("{:?}", FOO);
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Trying to directly mutate a `const` item is almost always a mistake.
    /// What is happening in the example above is that a temporary copy of the
    /// `const` is mutated, but the original `const` is not. Each time you
    /// refer to the `const` by name (such as `FOO` in the example above), a
    /// separate copy of the value is inlined at that location.
    ///
    /// This lint checks for writing directly to a field (`FOO.field =
    /// some_value`) or array entry (`FOO[0] = val`), or taking a mutable
    /// reference to the const item (`&mut FOO`), including through an
    /// autoderef (`FOO.some_mut_self_method()`).
    ///
    /// There are various alternatives depending on what you are trying to
    /// accomplish:
    ///
    /// * First, always reconsider using mutable globals, as they can be
    ///   difficult to use correctly, and can make the code more difficult to
    ///   use or understand.
    /// * If you are trying to perform a one-time initialization of a global:
    ///     * If the value can be computed at compile-time, consider using
    ///       const-compatible values (see [Constant Evaluation]).
    ///     * For more complex single-initialization cases, consider using a
    ///       third-party crate, such as [`lazy_static`] or [`once_cell`].
    ///     * If you are using the [nightly channel], consider the new
    ///       [`lazy`] module in the standard library.
    /// * If you truly need a mutable global, consider using a [`static`],
    ///   which has a variety of options:
    ///   * Simple data types can be directly defined and mutated with an
    ///     [`atomic`] type.
    ///   * More complex types can be placed in a synchronization primitive
    ///     like a [`Mutex`], which can be initialized with one of the options
    ///     listed above.
    ///   * A [mutable `static`] is a low-level primitive, requiring unsafe.
    ///     Typically This should be avoided in preference of something
    ///     higher-level like one of the above.
    ///
    /// [Constant Evaluation]: https://doc.rust-lang.org/reference/const_eval.html
    /// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
    /// [mutable `static`]: https://doc.rust-lang.org/reference/items/static-items.html#mutable-statics
    /// [`lazy`]: https://doc.rust-lang.org/nightly/std/lazy/index.html
    /// [`lazy_static`]: https://crates.io/crates/lazy_static
    /// [`once_cell`]: https://crates.io/crates/once_cell
    /// [`atomic`]: https://doc.rust-lang.org/std/sync/atomic/index.html
    /// [`Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
    pub CONST_ITEM_MUTATION,
    Warn,
    "detects attempts to mutate a `const` item",
}

declare_lint! {
    /// The `patterns_in_fns_without_body` lint detects `mut` identifier
    /// patterns as a parameter in functions without a body.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// trait Trait {
    ///     fn foo(mut arg: u8);
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// To fix this, remove `mut` from the parameter in the trait definition;
    /// it can be used in the implementation. That is, the following is OK:
    ///
    /// ```rust
    /// trait Trait {
    ///     fn foo(arg: u8); // Removed `mut` here
    /// }
    ///
    /// impl Trait for i32 {
    ///     fn foo(mut arg: u8) { // `mut` here is OK
    ///
    ///     }
    /// }
    /// ```
    ///
    /// Trait definitions can define functions without a body to specify a
    /// function that implementors must define. The parameter names in the
    /// body-less functions are only allowed to be `_` or an [identifier] for
    /// documentation purposes (only the type is relevant). Previous versions
    /// of the compiler erroneously allowed [identifier patterns] with the
    /// `mut` keyword, but this was not intended to be allowed. This is a
    /// [future-incompatible] lint to transition this to a hard error in the
    /// future. See [issue #35203] for more details.
    ///
    /// [identifier]: https://doc.rust-lang.org/reference/identifiers.html
    /// [identifier patterns]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
    /// [issue #35203]: https://github.com/rust-lang/rust/issues/35203
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub PATTERNS_IN_FNS_WITHOUT_BODY,
    Deny,
    "patterns in functions without body were erroneously allowed",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #35203 <https://github.com/rust-lang/rust/issues/35203>",
    };
}

declare_lint! {
    /// The `missing_fragment_specifier` lint is issued when an unused pattern in a
    /// `macro_rules!` macro definition has a meta-variable (e.g. `$e`) that is not
    /// followed by a fragment specifier (e.g. `:expr`).
    ///
    /// This warning can always be fixed by removing the unused pattern in the
    /// `macro_rules!` macro definition.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// macro_rules! foo {
    ///    () => {};
    ///    ($name) => { };
    /// }
    ///
    /// fn main() {
    ///    foo!();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// To fix this, remove the unused pattern from the `macro_rules!` macro definition:
    ///
    /// ```rust
    /// macro_rules! foo {
    ///     () => {};
    /// }
    /// fn main() {
    ///     foo!();
    /// }
    /// ```
    pub MISSING_FRAGMENT_SPECIFIER,
    Deny,
    "detects missing fragment specifiers in unused `macro_rules!` patterns",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #40107 <https://github.com/rust-lang/rust/issues/40107>",
    };
}

declare_lint! {
    /// The `late_bound_lifetime_arguments` lint detects generic lifetime
    /// arguments in path segments with late bound lifetime parameters.
    ///
    /// ### Example
    ///
    /// ```rust
    /// struct S;
    ///
    /// impl S {
    ///     fn late<'a, 'b>(self, _: &'a u8, _: &'b u8) {}
    /// }
    ///
    /// fn main() {
    ///     S.late::<'static>(&0, &0);
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// It is not clear how to provide arguments for early-bound lifetime
    /// parameters if they are intermixed with late-bound parameters in the
    /// same list. For now, providing any explicit arguments will trigger this
    /// lint if late-bound parameters are present, so in the future a solution
    /// can be adopted without hitting backward compatibility issues. This is
    /// a [future-incompatible] lint to transition this to a hard error in the
    /// future. See [issue #42868] for more details, along with a description
    /// of the difference between early and late-bound parameters.
    ///
    /// [issue #42868]: https://github.com/rust-lang/rust/issues/42868
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub LATE_BOUND_LIFETIME_ARGUMENTS,
    Warn,
    "detects generic lifetime arguments in path segments with late bound lifetime parameters",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #42868 <https://github.com/rust-lang/rust/issues/42868>",
    };
}

declare_lint! {
    /// The `order_dependent_trait_objects` lint detects a trait coherency
    /// violation that would allow creating two trait impls for the same
    /// dynamic trait object involving marker traits.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// pub trait Trait {}
    ///
    /// impl Trait for dyn Send + Sync { }
    /// impl Trait for dyn Sync + Send { }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// A previous bug caused the compiler to interpret traits with different
    /// orders (such as `Send + Sync` and `Sync + Send`) as distinct types
    /// when they were intended to be treated the same. This allowed code to
    /// define separate trait implementations when there should be a coherence
    /// error. This is a [future-incompatible] lint to transition this to a
    /// hard error in the future. See [issue #56484] for more details.
    ///
    /// [issue #56484]: https://github.com/rust-lang/rust/issues/56484
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub ORDER_DEPENDENT_TRAIT_OBJECTS,
    Deny,
    "trait-object types were treated as different depending on marker-trait order",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #56484 <https://github.com/rust-lang/rust/issues/56484>",
        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
    };
}

declare_lint! {
    /// The `coherence_leak_check` lint detects conflicting implementations of
    /// a trait that are only distinguished by the old leak-check code.
    ///
    /// ### Example
    ///
    /// ```rust
    /// trait SomeTrait { }
    /// impl SomeTrait for for<'a> fn(&'a u8) { }
    /// impl<'a> SomeTrait for fn(&'a u8) { }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In the past, the compiler would accept trait implementations for
    /// identical functions that differed only in where the lifetime binder
    /// appeared. Due to a change in the borrow checker implementation to fix
    /// several bugs, this is no longer allowed. However, since this affects
    /// existing code, this is a [future-incompatible] lint to transition this
    /// to a hard error in the future.
    ///
    /// Code relying on this pattern should introduce "[newtypes]",
    /// like `struct Foo(for<'a> fn(&'a u8))`.
    ///
    /// See [issue #56105] for more details.
    ///
    /// [issue #56105]: https://github.com/rust-lang/rust/issues/56105
    /// [newtypes]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#using-the-newtype-pattern-for-type-safety-and-abstraction
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub COHERENCE_LEAK_CHECK,
    Warn,
    "distinct impls distinguished only by the leak-check code",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #56105 <https://github.com/rust-lang/rust/issues/56105>",
    };
}

declare_lint! {
    /// The `deprecated` lint detects use of deprecated items.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #[deprecated]
    /// fn foo() {}
    ///
    /// fn bar() {
    ///     foo();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Items may be marked "deprecated" with the [`deprecated` attribute] to
    /// indicate that they should no longer be used. Usually the attribute
    /// should include a note on what to use instead, or check the
    /// documentation.
    ///
    /// [`deprecated` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute
    pub DEPRECATED,
    Warn,
    "detects use of deprecated items",
    report_in_external_macro
}

declare_lint! {
    /// The `unused_unsafe` lint detects unnecessary use of an `unsafe` block.
    ///
    /// ### Example
    ///
    /// ```rust
    /// unsafe {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// If nothing within the block requires `unsafe`, then remove the
    /// `unsafe` marker because it is not required and may cause confusion.
    pub UNUSED_UNSAFE,
    Warn,
    "unnecessary use of an `unsafe` block"
}

declare_lint! {
    /// The `unused_mut` lint detects mut variables which don't need to be
    /// mutable.
    ///
    /// ### Example
    ///
    /// ```rust
    /// let mut x = 5;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The preferred style is to only mark variables as `mut` if it is
    /// required.
    pub UNUSED_MUT,
    Warn,
    "detect mut variables which don't need to be mutable"
}

declare_lint! {
    /// The `unconditional_recursion` lint detects functions that cannot
    /// return without calling themselves.
    ///
    /// ### Example
    ///
    /// ```rust
    /// fn foo() {
    ///     foo();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// It is usually a mistake to have a recursive call that does not have
    /// some condition to cause it to terminate. If you really intend to have
    /// an infinite loop, using a `loop` expression is recommended.
    pub UNCONDITIONAL_RECURSION,
    Warn,
    "functions that cannot return without calling themselves"
}

declare_lint! {
    /// The `single_use_lifetimes` lint detects lifetimes that are only used
    /// once.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(single_use_lifetimes)]
    ///
    /// fn foo<'a>(x: &'a u32) {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Specifying an explicit lifetime like `'a` in a function or `impl`
    /// should only be used to link together two things. Otherwise, you should
    /// just use `'_` to indicate that the lifetime is not linked to anything,
    /// or elide the lifetime altogether if possible.
    ///
    /// This lint is "allow" by default because it was introduced at a time
    /// when `'_` and elided lifetimes were first being introduced, and this
    /// lint would be too noisy. Also, there are some known false positives
    /// that it produces. See [RFC 2115] for historical context, and [issue
    /// #44752] for more details.
    ///
    /// [RFC 2115]: https://github.com/rust-lang/rfcs/blob/master/text/2115-argument-lifetimes.md
    /// [issue #44752]: https://github.com/rust-lang/rust/issues/44752
    pub SINGLE_USE_LIFETIMES,
    Allow,
    "detects lifetime parameters that are only used once"
}

declare_lint! {
    /// The `unused_lifetimes` lint detects lifetime parameters that are never
    /// used.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #[deny(unused_lifetimes)]
    ///
    /// pub fn foo<'a>() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused lifetime parameters may signal a mistake or unfinished code.
    /// Consider removing the parameter.
    pub UNUSED_LIFETIMES,
    Allow,
    "detects lifetime parameters that are never used"
}

declare_lint! {
    /// The `tyvar_behind_raw_pointer` lint detects raw pointer to an
    /// inference variable.
    ///
    /// ### Example
    ///
    /// ```rust,edition2015
    /// // edition 2015
    /// let data = std::ptr::null();
    /// let _ = &data as *const *const ();
    ///
    /// if data.is_null() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// This kind of inference was previously allowed, but with the future
    /// arrival of [arbitrary self types], this can introduce ambiguity. To
    /// resolve this, use an explicit type instead of relying on type
    /// inference.
    ///
    /// This is a [future-incompatible] lint to transition this to a hard
    /// error in the 2018 edition. See [issue #46906] for more details. This
    /// is currently a hard-error on the 2018 edition, and is "warn" by
    /// default in the 2015 edition.
    ///
    /// [arbitrary self types]: https://github.com/rust-lang/rust/issues/44874
    /// [issue #46906]: https://github.com/rust-lang/rust/issues/46906
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub TYVAR_BEHIND_RAW_POINTER,
    Warn,
    "raw pointer to an inference variable",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #46906 <https://github.com/rust-lang/rust/issues/46906>",
        reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
    };
}

declare_lint! {
    /// The `elided_lifetimes_in_paths` lint detects the use of hidden
    /// lifetime parameters.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(elided_lifetimes_in_paths)]
    /// struct Foo<'a> {
    ///     x: &'a u32
    /// }
    ///
    /// fn foo(x: &Foo) {
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Elided lifetime parameters can make it difficult to see at a glance
    /// that borrowing is occurring. This lint ensures that lifetime
    /// parameters are always explicitly stated, even if it is the `'_`
    /// [placeholder lifetime].
    ///
    /// This lint is "allow" by default because it has some known issues, and
    /// may require a significant transition for old code.
    ///
    /// [placeholder lifetime]: https://doc.rust-lang.org/reference/lifetime-elision.html#lifetime-elision-in-functions
    pub ELIDED_LIFETIMES_IN_PATHS,
    Allow,
    "hidden lifetime parameters in types are deprecated",
    crate_level_only
}

declare_lint! {
    /// The `bare_trait_objects` lint suggests using `dyn Trait` for trait
    /// objects.
    ///
    /// ### Example
    ///
    /// ```rust,edition2018
    /// trait Trait { }
    ///
    /// fn takes_trait_object(_: Box<Trait>) {
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Without the `dyn` indicator, it can be ambiguous or confusing when
    /// reading code as to whether or not you are looking at a trait object.
    /// The `dyn` keyword makes it explicit, and adds a symmetry to contrast
    /// with [`impl Trait`].
    ///
    /// [`impl Trait`]: https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
    pub BARE_TRAIT_OBJECTS,
    Warn,
    "suggest using `dyn Trait` for trait objects",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
        reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
    };
}

declare_lint! {
    /// The `absolute_paths_not_starting_with_crate` lint detects fully
    /// qualified paths that start with a module name instead of `crate`,
    /// `self`, or an extern crate name
    ///
    /// ### Example
    ///
    /// ```rust,edition2015,compile_fail
    /// #![deny(absolute_paths_not_starting_with_crate)]
    ///
    /// mod foo {
    ///     pub fn bar() {}
    /// }
    ///
    /// fn main() {
    ///     ::foo::bar();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Rust [editions] allow the language to evolve without breaking
    /// backwards compatibility. This lint catches code that uses absolute
    /// paths in the style of the 2015 edition. In the 2015 edition, absolute
    /// paths (those starting with `::`) refer to either the crate root or an
    /// external crate. In the 2018 edition it was changed so that they only
    /// refer to external crates. The path prefix `crate::` should be used
    /// instead to reference items from the crate root.
    ///
    /// If you switch the compiler from the 2015 to 2018 edition without
    /// updating the code, then it will fail to compile if the old style paths
    /// are used. You can manually change the paths to use the `crate::`
    /// prefix to transition to the 2018 edition.
    ///
    /// This lint solves the problem automatically. It is "allow" by default
    /// because the code is perfectly valid in the 2015 edition. The [`cargo
    /// fix`] tool with the `--edition` flag will switch this lint to "warn"
    /// and automatically apply the suggested fix from the compiler. This
    /// provides a completely automated way to update old code to the 2018
    /// edition.
    ///
    /// [editions]: https://doc.rust-lang.org/edition-guide/
    /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
    pub ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
    Allow,
    "fully qualified paths that start with a module name \
     instead of `crate`, `self`, or an extern crate name",
     @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #53130 <https://github.com/rust-lang/rust/issues/53130>",
        reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
     };
}

declare_lint! {
    /// The `illegal_floating_point_literal_pattern` lint detects
    /// floating-point literals used in patterns.
    ///
    /// ### Example
    ///
    /// ```rust
    /// let x = 42.0;
    ///
    /// match x {
    ///     5.0 => {}
    ///     _ => {}
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Previous versions of the compiler accepted floating-point literals in
    /// patterns, but it was later determined this was a mistake. The
    /// semantics of comparing floating-point values may not be clear in a
    /// pattern when contrasted with "structural equality". Typically you can
    /// work around this by using a [match guard], such as:
    ///
    /// ```rust
    /// # let x = 42.0;
    ///
    /// match x {
    ///     y if y == 5.0 => {}
    ///     _ => {}
    /// }
    /// ```
    ///
    /// This is a [future-incompatible] lint to transition this to a hard
    /// error in the future. See [issue #41620] for more details.
    ///
    /// [issue #41620]: https://github.com/rust-lang/rust/issues/41620
    /// [match guard]: https://doc.rust-lang.org/reference/expressions/match-expr.html#match-guards
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
    Warn,
    "floating-point literals cannot be used in patterns",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #41620 <https://github.com/rust-lang/rust/issues/41620>",
    };
}

declare_lint! {
    /// The `unstable_name_collisions` lint detects that you have used a name
    /// that the standard library plans to add in the future.
    ///
    /// ### Example
    ///
    /// ```rust
    /// trait MyIterator : Iterator {
    ///     // is_sorted is an unstable method that already exists on the Iterator trait
    ///     fn is_sorted(self) -> bool where Self: Sized {true}
    /// }
    ///
    /// impl<T: ?Sized> MyIterator for T where T: Iterator { }
    ///
    /// let x = vec![1, 2, 3];
    /// let _ = x.iter().is_sorted();
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// When new methods are added to traits in the standard library, they are
    /// usually added in an "unstable" form which is only available on the
    /// [nightly channel] with a [`feature` attribute]. If there is any
    /// pre-existing code which extends a trait to have a method with the same
    /// name, then the names will collide. In the future, when the method is
    /// stabilized, this will cause an error due to the ambiguity. This lint
    /// is an early-warning to let you know that there may be a collision in
    /// the future. This can be avoided by adding type annotations to
    /// disambiguate which trait method you intend to call, such as
    /// `MyIterator::is_sorted(my_iter)` or renaming or removing the method.
    ///
    /// [nightly channel]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
    /// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
    pub UNSTABLE_NAME_COLLISIONS,
    Warn,
    "detects name collision with an existing but unstable method",
    @future_incompatible = FutureIncompatibleInfo {
        reason: FutureIncompatibilityReason::Custom(
            "once this associated item is added to the standard library, \
             the ambiguity may cause an error or change in behavior!"
        ),
        reference: "issue #48919 <https://github.com/rust-lang/rust/issues/48919>",
        // Note: this item represents future incompatibility of all unstable functions in the
        //       standard library, and thus should never be removed or changed to an error.
    };
}

declare_lint! {
    /// The `irrefutable_let_patterns` lint detects [irrefutable patterns]
    /// in [`if let`]s, [`while let`]s, and `if let` guards.
    ///
    /// ### Example
    ///
    /// ```rust
    /// if let _ = 123 {
    ///     println!("always runs!");
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// There usually isn't a reason to have an irrefutable pattern in an
    /// `if let` or `while let` statement, because the pattern will always match
    /// successfully. A [`let`] or [`loop`] statement will suffice. However,
    /// when generating code with a macro, forbidding irrefutable patterns
    /// would require awkward workarounds in situations where the macro
    /// doesn't know if the pattern is refutable or not. This lint allows
    /// macros to accept this form, while alerting for a possibly incorrect
    /// use in normal code.
    ///
    /// See [RFC 2086] for more details.
    ///
    /// [irrefutable patterns]: https://doc.rust-lang.org/reference/patterns.html#refutability
    /// [`if let`]: https://doc.rust-lang.org/reference/expressions/if-expr.html#if-let-expressions
    /// [`while let`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#predicate-pattern-loops
    /// [`let`]: https://doc.rust-lang.org/reference/statements.html#let-statements
    /// [`loop`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#infinite-loops
    /// [RFC 2086]: https://github.com/rust-lang/rfcs/blob/master/text/2086-allow-if-let-irrefutables.md
    pub IRREFUTABLE_LET_PATTERNS,
    Warn,
    "detects irrefutable patterns in `if let` and `while let` statements"
}

declare_lint! {
    /// The `unused_labels` lint detects [labels] that are never used.
    ///
    /// [labels]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#loop-labels
    ///
    /// ### Example
    ///
    /// ```rust,no_run
    /// 'unused_label: loop {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unused labels may signal a mistake or unfinished code. To silence the
    /// warning for the individual label, prefix it with an underscore such as
    /// `'_my_label:`.
    pub UNUSED_LABELS,
    Warn,
    "detects labels that are never used"
}

declare_lint! {
    /// The `where_clauses_object_safety` lint detects for [object safety] of
    /// [where clauses].
    ///
    /// [object safety]: https://doc.rust-lang.org/reference/items/traits.html#object-safety
    /// [where clauses]: https://doc.rust-lang.org/reference/items/generics.html#where-clauses
    ///
    /// ### Example
    ///
    /// ```rust,no_run
    /// trait Trait {}
    ///
    /// trait X { fn foo(&self) where Self: Trait; }
    ///
    /// impl X for () { fn foo(&self) {} }
    ///
    /// impl Trait for dyn X {}
    ///
    /// // Segfault at opt-level 0, SIGILL otherwise.
    /// pub fn main() { <dyn X as X>::foo(&()); }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The compiler previously allowed these object-unsafe bounds, which was
    /// incorrect. This is a [future-incompatible] lint to transition this to
    /// a hard error in the future. See [issue #51443] for more details.
    ///
    /// [issue #51443]: https://github.com/rust-lang/rust/issues/51443
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub WHERE_CLAUSES_OBJECT_SAFETY,
    Warn,
    "checks the object safety of where clauses",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #51443 <https://github.com/rust-lang/rust/issues/51443>",
    };
}

declare_lint! {
    /// The `macro_use_extern_crate` lint detects the use of the
    /// [`macro_use` attribute].
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs extern crate)
    /// #![deny(macro_use_extern_crate)]
    ///
    /// #[macro_use]
    /// extern crate serde_json;
    ///
    /// fn main() {
    ///     let _ = json!{{}};
    /// }
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// error: deprecated `#[macro_use]` attribute used to import macros should be replaced at use sites with a `use` item to import the macro instead
    ///  --> src/main.rs:3:1
    ///   |
    /// 3 | #[macro_use]
    ///   | ^^^^^^^^^^^^
    ///   |
    /// note: the lint level is defined here
    ///  --> src/main.rs:1:9
    ///   |
    /// 1 | #![deny(macro_use_extern_crate)]
    ///   |         ^^^^^^^^^^^^^^^^^^^^^^
    /// ```
    ///
    /// ### Explanation
    ///
    /// The [`macro_use` attribute] on an [`extern crate`] item causes
    /// macros in that external crate to be brought into the prelude of the
    /// crate, making the macros in scope everywhere. As part of the efforts
    /// to simplify handling of dependencies in the [2018 edition], the use of
    /// `extern crate` is being phased out. To bring macros from extern crates
    /// into scope, it is recommended to use a [`use` import].
    ///
    /// This lint is "allow" by default because this is a stylistic choice
    /// that has not been settled, see [issue #52043] for more information.
    ///
    /// [`macro_use` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#the-macro_use-attribute
    /// [`use` import]: https://doc.rust-lang.org/reference/items/use-declarations.html
    /// [issue #52043]: https://github.com/rust-lang/rust/issues/52043
    pub MACRO_USE_EXTERN_CRATE,
    Allow,
    "the `#[macro_use]` attribute is now deprecated in favor of using macros \
     via the module system"
}

declare_lint! {
    /// The `macro_expanded_macro_exports_accessed_by_absolute_paths` lint
    /// detects macro-expanded [`macro_export`] macros from the current crate
    /// that cannot be referred to by absolute paths.
    ///
    /// [`macro_export`]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// macro_rules! define_exported {
    ///     () => {
    ///         #[macro_export]
    ///         macro_rules! exported {
    ///             () => {};
    ///         }
    ///     };
    /// }
    ///
    /// define_exported!();
    ///
    /// fn main() {
    ///     crate::exported!();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The intent is that all macros marked with the `#[macro_export]`
    /// attribute are made available in the root of the crate. However, when a
    /// `macro_rules!` definition is generated by another macro, the macro
    /// expansion is unable to uphold this rule. This is a
    /// [future-incompatible] lint to transition this to a hard error in the
    /// future. See [issue #53495] for more details.
    ///
    /// [issue #53495]: https://github.com/rust-lang/rust/issues/53495
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
    Deny,
    "macro-expanded `macro_export` macros from the current crate \
     cannot be referred to by absolute paths",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #52234 <https://github.com/rust-lang/rust/issues/52234>",
    };
    crate_level_only
}

declare_lint! {
    /// The `explicit_outlives_requirements` lint detects unnecessary
    /// lifetime bounds that can be inferred.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// # #![allow(unused)]
    /// #![deny(explicit_outlives_requirements)]
    ///
    /// struct SharedRef<'a, T>
    /// where
    ///     T: 'a,
    /// {
    ///     data: &'a T,
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// If a `struct` contains a reference, such as `&'a T`, the compiler
    /// requires that `T` outlives the lifetime `'a`. This historically
    /// required writing an explicit lifetime bound to indicate this
    /// requirement. However, this can be overly explicit, causing clutter and
    /// unnecessary complexity. The language was changed to automatically
    /// infer the bound if it is not specified. Specifically, if the struct
    /// contains a reference, directly or indirectly, to `T` with lifetime
    /// `'x`, then it will infer that `T: 'x` is a requirement.
    ///
    /// This lint is "allow" by default because it can be noisy for existing
    /// code that already had these requirements. This is a stylistic choice,
    /// as it is still valid to explicitly state the bound. It also has some
    /// false positives that can cause confusion.
    ///
    /// See [RFC 2093] for more details.
    ///
    /// [RFC 2093]: https://github.com/rust-lang/rfcs/blob/master/text/2093-infer-outlives.md
    pub EXPLICIT_OUTLIVES_REQUIREMENTS,
    Allow,
    "outlives requirements can be inferred"
}

declare_lint! {
    /// The `indirect_structural_match` lint detects a `const` in a pattern
    /// that manually implements [`PartialEq`] and [`Eq`].
    ///
    /// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(indirect_structural_match)]
    ///
    /// struct NoDerive(i32);
    /// impl PartialEq for NoDerive { fn eq(&self, _: &Self) -> bool { false } }
    /// impl Eq for NoDerive { }
    /// #[derive(PartialEq, Eq)]
    /// struct WrapParam<T>(T);
    /// const WRAP_INDIRECT_PARAM: & &WrapParam<NoDerive> = & &WrapParam(NoDerive(0));
    /// fn main() {
    ///     match WRAP_INDIRECT_PARAM {
    ///         WRAP_INDIRECT_PARAM => { }
    ///         _ => { }
    ///     }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The compiler unintentionally accepted this form in the past. This is a
    /// [future-incompatible] lint to transition this to a hard error in the
    /// future. See [issue #62411] for a complete description of the problem,
    /// and some possible solutions.
    ///
    /// [issue #62411]: https://github.com/rust-lang/rust/issues/62411
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub INDIRECT_STRUCTURAL_MATCH,
    Warn,
    "constant used in pattern contains value of non-structural-match type in a field or a variant",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #62411 <https://github.com/rust-lang/rust/issues/62411>",
    };
}

declare_lint! {
    /// The `deprecated_in_future` lint is internal to rustc and should not be
    /// used by user code.
    ///
    /// This lint is only enabled in the standard library. It works with the
    /// use of `#[deprecated]` with a `since` field of a version in the future.
    /// This allows something to be marked as deprecated in a future version,
    /// and then this lint will ensure that the item is no longer used in the
    /// standard library. See the [stability documentation] for more details.
    ///
    /// [stability documentation]: https://rustc-dev-guide.rust-lang.org/stability.html#deprecated
    pub DEPRECATED_IN_FUTURE,
    Allow,
    "detects use of items that will be deprecated in a future version",
    report_in_external_macro
}

declare_lint! {
    /// The `pointer_structural_match` lint detects pointers used in patterns whose behaviour
    /// cannot be relied upon across compiler versions and optimization levels.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(pointer_structural_match)]
    /// fn foo(a: usize, b: usize) -> usize { a + b }
    /// const FOO: fn(usize, usize) -> usize = foo;
    /// fn main() {
    ///     match FOO {
    ///         FOO => {},
    ///         _ => {},
    ///     }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Previous versions of Rust allowed function pointers and wide raw pointers in patterns.
    /// While these work in many cases as expected by users, it is possible that due to
    /// optimizations pointers are "not equal to themselves" or pointers to different functions
    /// compare as equal during runtime. This is because LLVM optimizations can deduplicate
    /// functions if their bodies are the same, thus also making pointers to these functions point
    /// to the same location. Additionally functions may get duplicated if they are instantiated
    /// in different crates and not deduplicated again via LTO.
    pub POINTER_STRUCTURAL_MATCH,
    Allow,
    "pointers are not structural-match",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #62411 <https://github.com/rust-lang/rust/issues/70861>",
    };
}

declare_lint! {
    /// The `nontrivial_structural_match` lint detects constants that are used in patterns,
    /// whose type is not structural-match and whose initializer body actually uses values
    /// that are not structural-match. So `Option<NotStructuralMatch>` is ok if the constant
    /// is just `None`.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(nontrivial_structural_match)]
    ///
    /// #[derive(Copy, Clone, Debug)]
    /// struct NoDerive(u32);
    /// impl PartialEq for NoDerive { fn eq(&self, _: &Self) -> bool { false } }
    /// impl Eq for NoDerive { }
    /// fn main() {
    ///     const INDEX: Option<NoDerive> = [None, Some(NoDerive(10))][0];
    ///     match None { Some(_) => panic!("whoops"), INDEX => dbg!(INDEX), };
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Previous versions of Rust accepted constants in patterns, even if those constants' types
    /// did not have `PartialEq` derived. Thus the compiler falls back to runtime execution of
    /// `PartialEq`, which can report that two constants are not equal even if they are
    /// bit-equivalent.
    pub NONTRIVIAL_STRUCTURAL_MATCH,
    Warn,
    "constant used in pattern of non-structural-match type and the constant's initializer \
    expression contains values of non-structural-match types",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #73448 <https://github.com/rust-lang/rust/issues/73448>",
    };
}

declare_lint! {
    /// The `ambiguous_associated_items` lint detects ambiguity between
    /// [associated items] and [enum variants].
    ///
    /// [associated items]: https://doc.rust-lang.org/reference/items/associated-items.html
    /// [enum variants]: https://doc.rust-lang.org/reference/items/enumerations.html
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// enum E {
    ///     V
    /// }
    ///
    /// trait Tr {
    ///     type V;
    ///     fn foo() -> Self::V;
    /// }
    ///
    /// impl Tr for E {
    ///     type V = u8;
    ///     // `Self::V` is ambiguous because it may refer to the associated type or
    ///     // the enum variant.
    ///     fn foo() -> Self::V { 0 }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Previous versions of Rust did not allow accessing enum variants
    /// through [type aliases]. When this ability was added (see [RFC 2338]), this
    /// introduced some situations where it can be ambiguous what a type
    /// was referring to.
    ///
    /// To fix this ambiguity, you should use a [qualified path] to explicitly
    /// state which type to use. For example, in the above example the
    /// function can be written as `fn f() -> <Self as Tr>::V { 0 }` to
    /// specifically refer to the associated type.
    ///
    /// This is a [future-incompatible] lint to transition this to a hard
    /// error in the future. See [issue #57644] for more details.
    ///
    /// [issue #57644]: https://github.com/rust-lang/rust/issues/57644
    /// [type aliases]: https://doc.rust-lang.org/reference/items/type-aliases.html#type-aliases
    /// [RFC 2338]: https://github.com/rust-lang/rfcs/blob/master/text/2338-type-alias-enum-variants.md
    /// [qualified path]: https://doc.rust-lang.org/reference/paths.html#qualified-paths
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub AMBIGUOUS_ASSOCIATED_ITEMS,
    Deny,
    "ambiguous associated items",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #57644 <https://github.com/rust-lang/rust/issues/57644>",
    };
}

declare_lint! {
    /// The `soft_unstable` lint detects unstable features that were
    /// unintentionally allowed on stable.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #[cfg(test)]
    /// extern crate test;
    ///
    /// #[bench]
    /// fn name(b: &mut test::Bencher) {
    ///     b.iter(|| 123)
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The [`bench` attribute] was accidentally allowed to be specified on
    /// the [stable release channel]. Turning this to a hard error would have
    /// broken some projects. This lint allows those projects to continue to
    /// build correctly when [`--cap-lints`] is used, but otherwise signal an
    /// error that `#[bench]` should not be used on the stable channel. This
    /// is a [future-incompatible] lint to transition this to a hard error in
    /// the future. See [issue #64266] for more details.
    ///
    /// [issue #64266]: https://github.com/rust-lang/rust/issues/64266
    /// [`bench` attribute]: https://doc.rust-lang.org/nightly/unstable-book/library-features/test.html
    /// [stable release channel]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
    /// [`--cap-lints`]: https://doc.rust-lang.org/rustc/lints/levels.html#capping-lints
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub SOFT_UNSTABLE,
    Deny,
    "a feature gate that doesn't break dependent crates",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #64266 <https://github.com/rust-lang/rust/issues/64266>",
    };
}

declare_lint! {
    /// The `inline_no_sanitize` lint detects incompatible use of
    /// [`#[inline(always)]`][inline] and [`#[no_sanitize(...)]`][no_sanitize].
    ///
    /// [inline]: https://doc.rust-lang.org/reference/attributes/codegen.html#the-inline-attribute
    /// [no_sanitize]: https://doc.rust-lang.org/nightly/unstable-book/language-features/no-sanitize.html
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![feature(no_sanitize)]
    ///
    /// #[inline(always)]
    /// #[no_sanitize(address)]
    /// fn x() {}
    ///
    /// fn main() {
    ///     x()
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The use of the [`#[inline(always)]`][inline] attribute prevents the
    /// the [`#[no_sanitize(...)]`][no_sanitize] attribute from working.
    /// Consider temporarily removing `inline` attribute.
    pub INLINE_NO_SANITIZE,
    Warn,
    "detects incompatible use of `#[inline(always)]` and `#[no_sanitize(...)]`",
}

declare_lint! {
    /// The `asm_sub_register` lint detects using only a subset of a register
    /// for inline asm inputs.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (fails on non-x86_64)
    /// #[cfg(target_arch="x86_64")]
    /// use std::arch::asm;
    ///
    /// fn main() {
    ///     #[cfg(target_arch="x86_64")]
    ///     unsafe {
    ///         asm!("mov {0}, {0}", in(reg) 0i16);
    ///     }
    /// }
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: formatting may not be suitable for sub-register argument
    ///  --> src/main.rs:7:19
    ///   |
    /// 7 |         asm!("mov {0}, {0}", in(reg) 0i16);
    ///   |                   ^^^  ^^^           ---- for this argument
    ///   |
    ///   = note: `#[warn(asm_sub_register)]` on by default
    ///   = help: use the `x` modifier to have the register formatted as `ax`
    ///   = help: or use the `r` modifier to keep the default formatting of `rax`
    /// ```
    ///
    /// ### Explanation
    ///
    /// Registers on some architectures can use different names to refer to a
    /// subset of the register. By default, the compiler will use the name for
    /// the full register size. To explicitly use a subset of the register,
    /// you can override the default by using a modifier on the template
    /// string operand to specify when subregister to use. This lint is issued
    /// if you pass in a value with a smaller data type than the default
    /// register size, to alert you of possibly using the incorrect width. To
    /// fix this, add the suggested modifier to the template, or cast the
    /// value to the correct size.
    ///
    /// See [register template modifiers] in the reference for more details.
    ///
    /// [register template modifiers]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html#template-modifiers
    pub ASM_SUB_REGISTER,
    Warn,
    "using only a subset of a register for inline asm inputs",
}

declare_lint! {
    /// The `bad_asm_style` lint detects the use of the `.intel_syntax` and
    /// `.att_syntax` directives.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (fails on non-x86_64)
    /// #[cfg(target_arch="x86_64")]
    /// use std::arch::asm;
    ///
    /// fn main() {
    ///     #[cfg(target_arch="x86_64")]
    ///     unsafe {
    ///         asm!(
    ///             ".att_syntax",
    ///             "movq %{0}, %{0}", in(reg) 0usize
    ///         );
    ///     }
    /// }
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: avoid using `.att_syntax`, prefer using `options(att_syntax)` instead
    ///  --> src/main.rs:8:14
    ///   |
    /// 8 |             ".att_syntax",
    ///   |              ^^^^^^^^^^^
    ///   |
    ///   = note: `#[warn(bad_asm_style)]` on by default
    /// ```
    ///
    /// ### Explanation
    ///
    /// On x86, `asm!` uses the intel assembly syntax by default. While this
    /// can be switched using assembler directives like `.att_syntax`, using the
    /// `att_syntax` option is recommended instead because it will also properly
    /// prefix register placeholders with `%` as required by AT&T syntax.
    pub BAD_ASM_STYLE,
    Warn,
    "incorrect use of inline assembly",
}

declare_lint! {
    /// The `unsafe_op_in_unsafe_fn` lint detects unsafe operations in unsafe
    /// functions without an explicit unsafe block.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(unsafe_op_in_unsafe_fn)]
    ///
    /// unsafe fn foo() {}
    ///
    /// unsafe fn bar() {
    ///     foo();
    /// }
    ///
    /// fn main() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Currently, an [`unsafe fn`] allows any [unsafe] operation within its
    /// body. However, this can increase the surface area of code that needs
    /// to be scrutinized for proper behavior. The [`unsafe` block] provides a
    /// convenient way to make it clear exactly which parts of the code are
    /// performing unsafe operations. In the future, it is desired to change
    /// it so that unsafe operations cannot be performed in an `unsafe fn`
    /// without an `unsafe` block.
    ///
    /// The fix to this is to wrap the unsafe code in an `unsafe` block.
    ///
    /// This lint is "allow" by default since this will affect a large amount
    /// of existing code, and the exact plan for increasing the severity is
    /// still being considered. See [RFC #2585] and [issue #71668] for more
    /// details.
    ///
    /// [`unsafe fn`]: https://doc.rust-lang.org/reference/unsafe-functions.html
    /// [`unsafe` block]: https://doc.rust-lang.org/reference/expressions/block-expr.html#unsafe-blocks
    /// [unsafe]: https://doc.rust-lang.org/reference/unsafety.html
    /// [RFC #2585]: https://github.com/rust-lang/rfcs/blob/master/text/2585-unsafe-block-in-unsafe-fn.md
    /// [issue #71668]: https://github.com/rust-lang/rust/issues/71668
    pub UNSAFE_OP_IN_UNSAFE_FN,
    Allow,
    "unsafe operations in unsafe functions without an explicit unsafe block are deprecated",
}

declare_lint! {
    /// The `cenum_impl_drop_cast` lint detects an `as` cast of a field-less
    /// `enum` that implements [`Drop`].
    ///
    /// [`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// # #![allow(unused)]
    /// enum E {
    ///     A,
    /// }
    ///
    /// impl Drop for E {
    ///     fn drop(&mut self) {
    ///         println!("Drop");
    ///     }
    /// }
    ///
    /// fn main() {
    ///     let e = E::A;
    ///     let i = e as u32;
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Casting a field-less `enum` that does not implement [`Copy`] to an
    /// integer moves the value without calling `drop`. This can result in
    /// surprising behavior if it was expected that `drop` should be called.
    /// Calling `drop` automatically would be inconsistent with other move
    /// operations. Since neither behavior is clear or consistent, it was
    /// decided that a cast of this nature will no longer be allowed.
    ///
    /// This is a [future-incompatible] lint to transition this to a hard error
    /// in the future. See [issue #73333] for more details.
    ///
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    /// [issue #73333]: https://github.com/rust-lang/rust/issues/73333
    /// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
    pub CENUM_IMPL_DROP_CAST,
    Deny,
    "a C-like enum implementing Drop is cast",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #73333 <https://github.com/rust-lang/rust/issues/73333>",
        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
    };
}

declare_lint! {
    /// The `fuzzy_provenance_casts` lint detects an `as` cast between an integer
    /// and a pointer.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![feature(strict_provenance)]
    /// #![warn(fuzzy_provenance_casts)]
    ///
    /// fn main() {
    ///     let _dangling = 16_usize as *const u8;
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// This lint is part of the strict provenance effort, see [issue #95228].
    /// Casting an integer to a pointer is considered bad style, as a pointer
    /// contains, besides the *address* also a *provenance*, indicating what
    /// memory the pointer is allowed to read/write. Casting an integer, which
    /// doesn't have provenance, to a pointer requires the compiler to assign
    /// (guess) provenance. The compiler assigns "all exposed valid" (see the
    /// docs of [`ptr::from_exposed_addr`] for more information about this
    /// "exposing"). This penalizes the optimiser and is not well suited for
    /// dynamic analysis/dynamic program verification (e.g. Miri or CHERI
    /// platforms).
    ///
    /// It is much better to use [`ptr::with_addr`] instead to specify the
    /// provenance you want. If using this function is not possible because the
    /// code relies on exposed provenance then there is as an escape hatch
    /// [`ptr::from_exposed_addr`].
    ///
    /// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
    /// [`ptr::with_addr`]: https://doc.rust-lang.org/core/ptr/fn.with_addr
    /// [`ptr::from_exposed_addr`]: https://doc.rust-lang.org/core/ptr/fn.from_exposed_addr
    pub FUZZY_PROVENANCE_CASTS,
    Allow,
    "a fuzzy integer to pointer cast is used",
    @feature_gate = sym::strict_provenance;
}

declare_lint! {
    /// The `lossy_provenance_casts` lint detects an `as` cast between a pointer
    /// and an integer.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![feature(strict_provenance)]
    /// #![warn(lossy_provenance_casts)]
    ///
    /// fn main() {
    ///     let x: u8 = 37;
    ///     let _addr: usize = &x as *const u8 as usize;
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// This lint is part of the strict provenance effort, see [issue #95228].
    /// Casting a pointer to an integer is a lossy operation, because beyond
    /// just an *address* a pointer may be associated with a particular
    /// *provenance*. This information is used by the optimiser and for dynamic
    /// analysis/dynamic program verification (e.g. Miri or CHERI platforms).
    ///
    /// Since this cast is lossy, it is considered good style to use the
    /// [`ptr::addr`] method instead, which has a similar effect, but doesn't
    /// "expose" the pointer provenance. This improves optimisation potential.
    /// See the docs of [`ptr::addr`] and [`ptr::expose_addr`] for more information
    /// about exposing pointer provenance.
    ///
    /// If your code can't comply with strict provenance and needs to expose
    /// the provenance, then there is [`ptr::expose_addr`] as an escape hatch,
    /// which preserves the behaviour of `as usize` casts while being explicit
    /// about the semantics.
    ///
    /// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
    /// [`ptr::addr`]: https://doc.rust-lang.org/core/ptr/fn.addr
    /// [`ptr::expose_addr`]: https://doc.rust-lang.org/core/ptr/fn.expose_addr
    pub LOSSY_PROVENANCE_CASTS,
    Allow,
    "a lossy pointer to integer cast is used",
    @feature_gate = sym::strict_provenance;
}

declare_lint! {
    /// The `const_evaluatable_unchecked` lint detects a generic constant used
    /// in a type.
    ///
    /// ### Example
    ///
    /// ```rust
    /// const fn foo<T>() -> usize {
    ///     if std::mem::size_of::<*mut T>() < 8 { // size of *mut T does not depend on T
    ///         4
    ///     } else {
    ///         8
    ///     }
    /// }
    ///
    /// fn test<T>() {
    ///     let _ = [0; foo::<T>()];
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In the 1.43 release, some uses of generic parameters in array repeat
    /// expressions were accidentally allowed. This is a [future-incompatible]
    /// lint to transition this to a hard error in the future. See [issue
    /// #76200] for a more detailed description and possible fixes.
    ///
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    /// [issue #76200]: https://github.com/rust-lang/rust/issues/76200
    pub CONST_EVALUATABLE_UNCHECKED,
    Warn,
    "detects a generic constant is used in a type without a emitting a warning",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #76200 <https://github.com/rust-lang/rust/issues/76200>",
    };
}

declare_lint! {
    /// The `function_item_references` lint detects function references that are
    /// formatted with [`fmt::Pointer`] or transmuted.
    ///
    /// [`fmt::Pointer`]: https://doc.rust-lang.org/std/fmt/trait.Pointer.html
    ///
    /// ### Example
    ///
    /// ```rust
    /// fn foo() { }
    ///
    /// fn main() {
    ///     println!("{:p}", &foo);
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Taking a reference to a function may be mistaken as a way to obtain a
    /// pointer to that function. This can give unexpected results when
    /// formatting the reference as a pointer or transmuting it. This lint is
    /// issued when function references are formatted as pointers, passed as
    /// arguments bound by [`fmt::Pointer`] or transmuted.
    pub FUNCTION_ITEM_REFERENCES,
    Warn,
    "suggest casting to a function pointer when attempting to take references to function items",
}

declare_lint! {
    /// The `uninhabited_static` lint detects uninhabited statics.
    ///
    /// ### Example
    ///
    /// ```rust
    /// enum Void {}
    /// extern {
    ///     static EXTERN: Void;
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Statics with an uninhabited type can never be initialized, so they are impossible to define.
    /// However, this can be side-stepped with an `extern static`, leading to problems later in the
    /// compiler which assumes that there are no initialized uninhabited places (such as locals or
    /// statics). This was accidentally allowed, but is being phased out.
    pub UNINHABITED_STATIC,
    Warn,
    "uninhabited static",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #74840 <https://github.com/rust-lang/rust/issues/74840>",
    };
}

declare_lint! {
    /// The `useless_deprecated` lint detects deprecation attributes with no effect.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// struct X;
    ///
    /// #[deprecated = "message"]
    /// impl Default for X {
    ///     fn default() -> Self {
    ///         X
    ///     }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Deprecation attributes have no effect on trait implementations.
    pub USELESS_DEPRECATED,
    Deny,
    "detects deprecation attributes with no effect",
}

declare_lint! {
    /// The `undefined_naked_function_abi` lint detects naked function definitions that
    /// either do not specify an ABI or specify the Rust ABI.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![feature(asm_experimental_arch, naked_functions)]
    ///
    /// use std::arch::asm;
    ///
    /// #[naked]
    /// pub fn default_abi() -> u32 {
    ///     unsafe { asm!("", options(noreturn)); }
    /// }
    ///
    /// #[naked]
    /// pub extern "Rust" fn rust_abi() -> u32 {
    ///     unsafe { asm!("", options(noreturn)); }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The Rust ABI is currently undefined. Therefore, naked functions should
    /// specify a non-Rust ABI.
    pub UNDEFINED_NAKED_FUNCTION_ABI,
    Warn,
    "undefined naked function ABI"
}

declare_lint! {
    /// The `ineffective_unstable_trait_impl` lint detects `#[unstable]` attributes which are not used.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![feature(staged_api)]
    ///
    /// #[derive(Clone)]
    /// #[stable(feature = "x", since = "1")]
    /// struct S {}
    ///
    /// #[unstable(feature = "y", issue = "none")]
    /// impl Copy for S {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// `staged_api` does not currently support using a stability attribute on `impl` blocks.
    /// `impl`s are always stable if both the type and trait are stable, and always unstable otherwise.
    pub INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
    Deny,
    "detects `#[unstable]` on stable trait implementations for stable types"
}

declare_lint! {
    /// The `semicolon_in_expressions_from_macros` lint detects trailing semicolons
    /// in macro bodies when the macro is invoked in expression position.
    /// This was previous accepted, but is being phased out.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(semicolon_in_expressions_from_macros)]
    /// macro_rules! foo {
    ///     () => { true; }
    /// }
    ///
    /// fn main() {
    ///     let val = match true {
    ///         true => false,
    ///         _ => foo!()
    ///     };
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Previous, Rust ignored trailing semicolon in a macro
    /// body when a macro was invoked in expression position.
    /// However, this makes the treatment of semicolons in the language
    /// inconsistent, and could lead to unexpected runtime behavior
    /// in some circumstances (e.g. if the macro author expects
    /// a value to be dropped).
    ///
    /// This is a [future-incompatible] lint to transition this
    /// to a hard error in the future. See [issue #79813] for more details.
    ///
    /// [issue #79813]: https://github.com/rust-lang/rust/issues/79813
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
    Warn,
    "trailing semicolon in macro body used as expression",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #79813 <https://github.com/rust-lang/rust/issues/79813>",
    };
}

declare_lint! {
    /// The `legacy_derive_helpers` lint detects derive helper attributes
    /// that are used before they are introduced.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs extern crate)
    /// #[serde(rename_all = "camelCase")]
    /// #[derive(Deserialize)]
    /// struct S { /* fields */ }
    /// ```
    ///
    /// produces:
    ///
    /// ```text
    /// warning: derive helper attribute is used before it is introduced
    ///   --> $DIR/legacy-derive-helpers.rs:1:3
    ///    |
    ///  1 | #[serde(rename_all = "camelCase")]
    ///    |   ^^^^^
    /// ...
    ///  2 | #[derive(Deserialize)]
    ///    |          ----------- the attribute is introduced here
    /// ```
    ///
    /// ### Explanation
    ///
    /// Attributes like this work for historical reasons, but attribute expansion works in
    /// left-to-right order in general, so, to resolve `#[serde]`, compiler has to try to "look
    /// into the future" at not yet expanded part of the item , but such attempts are not always
    /// reliable.
    ///
    /// To fix the warning place the helper attribute after its corresponding derive.
    /// ```rust,ignore (needs extern crate)
    /// #[derive(Deserialize)]
    /// #[serde(rename_all = "camelCase")]
    /// struct S { /* fields */ }
    /// ```
    pub LEGACY_DERIVE_HELPERS,
    Warn,
    "detects derive helper attributes that are used before they are introduced",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #79202 <https://github.com/rust-lang/rust/issues/79202>",
    };
}

declare_lint! {
    /// The `large_assignments` lint detects when objects of large
    /// types are being moved around.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (can crash on some platforms)
    /// let x = [0; 50000];
    /// let y = x;
    /// ```
    ///
    /// produces:
    ///
    /// ```text
    /// warning: moving a large value
    ///   --> $DIR/move-large.rs:1:3
    ///   let y = x;
    ///           - Copied large value here
    /// ```
    ///
    /// ### Explanation
    ///
    /// When using a large type in a plain assignment or in a function
    /// argument, idiomatic code can be inefficient.
    /// Ideally appropriate optimizations would resolve this, but such
    /// optimizations are only done in a best-effort manner.
    /// This lint will trigger on all sites of large moves and thus allow the
    /// user to resolve them in code.
    pub LARGE_ASSIGNMENTS,
    Warn,
    "detects large moves or copies",
}

declare_lint! {
    /// The `deprecated_cfg_attr_crate_type_name` lint detects uses of the
    /// `#![cfg_attr(..., crate_type = "...")]` and
    /// `#![cfg_attr(..., crate_name = "...")]` attributes to conditionally
    /// specify the crate type and name in the source code.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![cfg_attr(debug_assertions, crate_type = "lib")]
    /// ```
    ///
    /// {{produces}}
    ///
    ///
    /// ### Explanation
    ///
    /// The `#![crate_type]` and `#![crate_name]` attributes require a hack in
    /// the compiler to be able to change the used crate type and crate name
    /// after macros have been expanded. Neither attribute works in combination
    /// with Cargo as it explicitly passes `--crate-type` and `--crate-name` on
    /// the commandline. These values must match the value used in the source
    /// code to prevent an error.
    ///
    /// To fix the warning use `--crate-type` on the commandline when running
    /// rustc instead of `#![cfg_attr(..., crate_type = "...")]` and
    /// `--crate-name` instead of `#![cfg_attr(..., crate_name = "...")]`.
    pub DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
    Deny,
    "detects usage of `#![cfg_attr(..., crate_type/crate_name = \"...\")]`",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #91632 <https://github.com/rust-lang/rust/issues/91632>",
    };
}

declare_lint! {
    /// The `unexpected_cfgs` lint detects unexpected conditional compilation conditions.
    ///
    /// ### Example
    ///
    /// ```text
    /// rustc --check-cfg 'names()'
    /// ```
    ///
    /// ```rust,ignore (needs command line option)
    /// #[cfg(widnows)]
    /// fn foo() {}
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: unknown condition name used
    ///  --> lint_example.rs:1:7
    ///   |
    /// 1 | #[cfg(widnows)]
    ///   |       ^^^^^^^
    ///   |
    ///   = note: `#[warn(unexpected_cfgs)]` on by default
    /// ```
    ///
    /// ### Explanation
    ///
    /// This lint is only active when a `--check-cfg='names(...)'` option has been passed
    /// to the compiler and triggers whenever an unknown condition name or value is used.
    /// The known condition include names or values passed in `--check-cfg`, `--cfg`, and some
    /// well-knows names and values built into the compiler.
    pub UNEXPECTED_CFGS,
    Warn,
    "detects unexpected names and values in `#[cfg]` conditions",
}

declare_lint! {
    /// The `repr_transparent_external_private_fields` lint
    /// detects types marked `#[repr(transparent)]` that (transitively)
    /// contain an external ZST type marked `#[non_exhaustive]` or containing
    /// private fields
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs external crate)
    /// #![deny(repr_transparent_external_private_fields)]
    /// use foo::NonExhaustiveZst;
    ///
    /// #[repr(transparent)]
    /// struct Bar(u32, ([u32; 0], NonExhaustiveZst));
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// error: zero-sized fields in repr(transparent) cannot contain external non-exhaustive types
    ///  --> src/main.rs:5:28
    ///   |
    /// 5 | struct Bar(u32, ([u32; 0], NonExhaustiveZst));
    ///   |                            ^^^^^^^^^^^^^^^^
    ///   |
    /// note: the lint level is defined here
    ///  --> src/main.rs:1:9
    ///   |
    /// 1 | #![deny(repr_transparent_external_private_fields)]
    ///   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ///   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    ///   = note: for more information, see issue #78586 <https://github.com/rust-lang/rust/issues/78586>
    ///   = note: this struct contains `NonExhaustiveZst`, which is marked with `#[non_exhaustive]`, and makes it not a breaking change to become non-zero-sized in the future.
    /// ```
    ///
    /// ### Explanation
    ///
    /// Previous, Rust accepted fields that contain external private zero-sized types,
    /// even though it should not be a breaking change to add a non-zero-sized field to
    /// that private type.
    ///
    /// This is a [future-incompatible] lint to transition this
    /// to a hard error in the future. See [issue #78586] for more details.
    ///
    /// [issue #78586]: https://github.com/rust-lang/rust/issues/78586
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
    Warn,
    "transparent type contains an external ZST that is marked #[non_exhaustive] or contains private fields",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #78586 <https://github.com/rust-lang/rust/issues/78586>",
    };
}

declare_lint! {
    /// The `unstable_syntax_pre_expansion` lint detects the use of unstable
    /// syntax that is discarded during attribute expansion.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #[cfg(FALSE)]
    /// macro foo() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The input to active attributes such as `#[cfg]` or procedural macro
    /// attributes is required to be valid syntax. Previously, the compiler only
    /// gated the use of unstable syntax features after resolving `#[cfg]` gates
    /// and expanding procedural macros.
    ///
    /// To avoid relying on unstable syntax, move the use of unstable syntax
    /// into a position where the compiler does not parse the syntax, such as a
    /// functionlike macro.
    ///
    /// ```rust
    /// # #![deny(unstable_syntax_pre_expansion)]
    ///
    /// macro_rules! identity {
    ///    ( $($tokens:tt)* ) => { $($tokens)* }
    /// }
    ///
    /// #[cfg(FALSE)]
    /// identity! {
    ///    macro foo() {}
    /// }
    /// ```
    ///
    /// This is a [future-incompatible] lint to transition this
    /// to a hard error in the future. See [issue #65860] for more details.
    ///
    /// [issue #65860]: https://github.com/rust-lang/rust/issues/65860
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub UNSTABLE_SYNTAX_PRE_EXPANSION,
    Warn,
    "unstable syntax can change at any point in the future, causing a hard error!",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #65860 <https://github.com/rust-lang/rust/issues/65860>",
    };
}

declare_lint_pass! {
    /// Does nothing as a lint pass, but registers some `Lint`s
    /// that are used by other parts of the compiler.
    HardwiredLints => [
        FORBIDDEN_LINT_GROUPS,
        ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
        ARITHMETIC_OVERFLOW,
        UNCONDITIONAL_PANIC,
        UNUSED_IMPORTS,
        UNUSED_EXTERN_CRATES,
        UNUSED_CRATE_DEPENDENCIES,
        UNUSED_QUALIFICATIONS,
        UNKNOWN_LINTS,
        UNFULFILLED_LINT_EXPECTATIONS,
        UNUSED_VARIABLES,
        UNUSED_ASSIGNMENTS,
        DEAD_CODE,
        UNREACHABLE_CODE,
        UNREACHABLE_PATTERNS,
        OVERLAPPING_RANGE_ENDPOINTS,
        BINDINGS_WITH_VARIANT_NAME,
        UNUSED_MACROS,
        UNUSED_MACRO_RULES,
        WARNINGS,
        UNUSED_FEATURES,
        STABLE_FEATURES,
        UNKNOWN_CRATE_TYPES,
        TRIVIAL_CASTS,
        TRIVIAL_NUMERIC_CASTS,
        PRIVATE_IN_PUBLIC,
        EXPORTED_PRIVATE_DEPENDENCIES,
        PUB_USE_OF_PRIVATE_EXTERN_CRATE,
        INVALID_TYPE_PARAM_DEFAULT,
        RENAMED_AND_REMOVED_LINTS,
        UNALIGNED_REFERENCES,
        CONST_ITEM_MUTATION,
        PATTERNS_IN_FNS_WITHOUT_BODY,
        MISSING_FRAGMENT_SPECIFIER,
        LATE_BOUND_LIFETIME_ARGUMENTS,
        ORDER_DEPENDENT_TRAIT_OBJECTS,
        COHERENCE_LEAK_CHECK,
        DEPRECATED,
        UNUSED_UNSAFE,
        UNUSED_MUT,
        UNCONDITIONAL_RECURSION,
        SINGLE_USE_LIFETIMES,
        UNUSED_LIFETIMES,
        UNUSED_LABELS,
        TYVAR_BEHIND_RAW_POINTER,
        ELIDED_LIFETIMES_IN_PATHS,
        BARE_TRAIT_OBJECTS,
        ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
        UNSTABLE_NAME_COLLISIONS,
        IRREFUTABLE_LET_PATTERNS,
        WHERE_CLAUSES_OBJECT_SAFETY,
        MACRO_USE_EXTERN_CRATE,
        MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
        ILL_FORMED_ATTRIBUTE_INPUT,
        CONFLICTING_REPR_HINTS,
        META_VARIABLE_MISUSE,
        DEPRECATED_IN_FUTURE,
        AMBIGUOUS_ASSOCIATED_ITEMS,
        INDIRECT_STRUCTURAL_MATCH,
        POINTER_STRUCTURAL_MATCH,
        NONTRIVIAL_STRUCTURAL_MATCH,
        SOFT_UNSTABLE,
        UNSTABLE_SYNTAX_PRE_EXPANSION,
        INLINE_NO_SANITIZE,
        BAD_ASM_STYLE,
        ASM_SUB_REGISTER,
        UNSAFE_OP_IN_UNSAFE_FN,
        INCOMPLETE_INCLUDE,
        CENUM_IMPL_DROP_CAST,
        FUZZY_PROVENANCE_CASTS,
        LOSSY_PROVENANCE_CASTS,
        CONST_EVALUATABLE_UNCHECKED,
        INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
        MUST_NOT_SUSPEND,
        UNINHABITED_STATIC,
        FUNCTION_ITEM_REFERENCES,
        USELESS_DEPRECATED,
        MISSING_ABI,
        INVALID_DOC_ATTRIBUTES,
        SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
        RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
        LEGACY_DERIVE_HELPERS,
        PROC_MACRO_BACK_COMPAT,
        RUST_2021_INCOMPATIBLE_OR_PATTERNS,
        LARGE_ASSIGNMENTS,
        RUST_2021_PRELUDE_COLLISIONS,
        RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
        UNSUPPORTED_CALLING_CONVENTIONS,
        BREAK_WITH_LABEL_AND_LOOP,
        UNUSED_ATTRIBUTES,
        UNUSED_TUPLE_STRUCT_FIELDS,
        NON_EXHAUSTIVE_OMITTED_PATTERNS,
        TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
        DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
        DUPLICATE_MACRO_ATTRIBUTES,
        SUSPICIOUS_AUTO_TRAIT_IMPLS,
        DEPRECATED_WHERE_CLAUSE_LOCATION,
        TEST_UNSTABLE_LINT,
        FFI_UNWIND_CALLS,
        REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
        NAMED_ARGUMENTS_USED_POSITIONALLY,
    ]
}

declare_lint! {
    /// The `unused_doc_comments` lint detects doc comments that aren't used
    /// by `rustdoc`.
    ///
    /// ### Example
    ///
    /// ```rust
    /// /// docs for x
    /// let x = 12;
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// `rustdoc` does not use doc comments in all positions, and so the doc
    /// comment will be ignored. Try changing it to a normal comment with `//`
    /// to avoid the warning.
    pub UNUSED_DOC_COMMENTS,
    Warn,
    "detects doc comments that aren't used by rustdoc"
}

declare_lint! {
    /// The `rust_2021_incompatible_closure_captures` lint detects variables that aren't completely
    /// captured in Rust 2021, such that the `Drop` order of their fields may differ between
    /// Rust 2018 and 2021.
    ///
    /// It can also detect when a variable implements a trait like `Send`, but one of its fields does not,
    /// and the field is captured by a closure and used with the assumption that said field implements
    /// the same trait as the root variable.
    ///
    /// ### Example of drop reorder
    ///
    /// ```rust,edition2018,compile_fail
    /// #![deny(rust_2021_incompatible_closure_captures)]
    /// # #![allow(unused)]
    ///
    /// struct FancyInteger(i32);
    ///
    /// impl Drop for FancyInteger {
    ///     fn drop(&mut self) {
    ///         println!("Just dropped {}", self.0);
    ///     }
    /// }
    ///
    /// struct Point { x: FancyInteger, y: FancyInteger }
    ///
    /// fn main() {
    ///   let p = Point { x: FancyInteger(10), y: FancyInteger(20) };
    ///
    ///   let c = || {
    ///      let x = p.x;
    ///   };
    ///
    ///   c();
    ///
    ///   // ... More code ...
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In the above example, `p.y` will be dropped at the end of `f` instead of
    /// with `c` in Rust 2021.
    ///
    /// ### Example of auto-trait
    ///
    /// ```rust,edition2018,compile_fail
    /// #![deny(rust_2021_incompatible_closure_captures)]
    /// use std::thread;
    ///
    /// struct Pointer(*mut i32);
    /// unsafe impl Send for Pointer {}
    ///
    /// fn main() {
    ///     let mut f = 10;
    ///     let fptr = Pointer(&mut f as *mut i32);
    ///     thread::spawn(move || unsafe {
    ///         *fptr.0 = 20;
    ///     });
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In the above example, only `fptr.0` is captured in Rust 2021.
    /// The field is of type `*mut i32`, which doesn't implement `Send`,
    /// making the code invalid as the field cannot be sent between threads safely.
    pub RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
    Allow,
    "detects closures affected by Rust 2021 changes",
    @future_incompatible = FutureIncompatibleInfo {
        reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
        explain_reason: false,
    };
}

declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);

declare_lint! {
    /// The `missing_abi` lint detects cases where the ABI is omitted from
    /// extern declarations.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(missing_abi)]
    ///
    /// extern fn foo() {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Historically, Rust implicitly selected C as the ABI for extern
    /// declarations. We expect to add new ABIs, like `C-unwind`, in the future,
    /// though this has not yet happened, and especially with their addition
    /// seeing the ABI easily will make code review easier.
    pub MISSING_ABI,
    Allow,
    "No declared ABI for extern declaration"
}

declare_lint! {
    /// The `invalid_doc_attributes` lint detects when the `#[doc(...)]` is
    /// misused.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(warnings)]
    ///
    /// pub mod submodule {
    ///     #![doc(test(no_crate_inject))]
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Previously, there were very like checks being performed on `#[doc(..)]`
    /// unlike the other attributes. It'll now catch all the issues that it
    /// silently ignored previously.
    pub INVALID_DOC_ATTRIBUTES,
    Warn,
    "detects invalid `#[doc(...)]` attributes",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #82730 <https://github.com/rust-lang/rust/issues/82730>",
    };
}

declare_lint! {
    /// The `proc_macro_back_compat` lint detects uses of old versions of certain
    /// proc-macro crates, which have hardcoded workarounds in the compiler.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs-dependency)
    ///
    /// use time_macros_impl::impl_macros;
    /// struct Foo;
    /// impl_macros!(Foo);
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: using an old version of `time-macros-impl`
    ///   ::: $DIR/group-compat-hack.rs:27:5
    ///    |
    /// LL |     impl_macros!(Foo);
    ///    |     ------------------ in this macro invocation
    ///    |
    ///    = note: `#[warn(proc_macro_back_compat)]` on by default
    ///    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    ///    = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
    ///    = note: the `time-macros-impl` crate will stop compiling in futures version of Rust. Please update to the latest version of the `time` crate to avoid breakage
    ///    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
    /// ```
    ///
    /// ### Explanation
    ///
    /// Eventually, the backwards-compatibility hacks present in the compiler will be removed,
    /// causing older versions of certain crates to stop compiling.
    /// This is a [future-incompatible] lint to ease the transition to an error.
    /// See [issue #83125] for more details.
    ///
    /// [issue #83125]: https://github.com/rust-lang/rust/issues/83125
    /// [future-incompatible]: ../index.md#future-incompatible-lints
    pub PROC_MACRO_BACK_COMPAT,
    Deny,
    "detects usage of old versions of certain proc-macro crates",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #83125 <https://github.com/rust-lang/rust/issues/83125>",
        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
    };
}

declare_lint! {
    /// The `rust_2021_incompatible_or_patterns` lint detects usage of old versions of or-patterns.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(rust_2021_incompatible_or_patterns)]
    ///
    /// macro_rules! match_any {
    ///     ( $expr:expr , $( $( $pat:pat )|+ => $expr_arm:expr ),+ ) => {
    ///         match $expr {
    ///             $(
    ///                 $( $pat => $expr_arm, )+
    ///             )+
    ///         }
    ///     };
    /// }
    ///
    /// fn main() {
    ///     let result: Result<i64, i32> = Err(42);
    ///     let int: i64 = match_any!(result, Ok(i) | Err(i) => i.into());
    ///     assert_eq!(int, 42);
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In Rust 2021, the `pat` matcher will match additional patterns, which include the `|` character.
    pub RUST_2021_INCOMPATIBLE_OR_PATTERNS,
    Allow,
    "detects usage of old versions of or-patterns",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/or-patterns-macro-rules.html>",
        reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
    };
}

declare_lint! {
    /// The `rust_2021_prelude_collisions` lint detects the usage of trait methods which are ambiguous
    /// with traits added to the prelude in future editions.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(rust_2021_prelude_collisions)]
    ///
    /// trait Foo {
    ///     fn try_into(self) -> Result<String, !>;
    /// }
    ///
    /// impl Foo for &str {
    ///     fn try_into(self) -> Result<String, !> {
    ///         Ok(String::from(self))
    ///     }
    /// }
    ///
    /// fn main() {
    ///     let x: String = "3".try_into().unwrap();
    ///     //                  ^^^^^^^^
    ///     // This call to try_into matches both Foo:try_into and TryInto::try_into as
    ///     // `TryInto` has been added to the Rust prelude in 2021 edition.
    ///     println!("{x}");
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In Rust 2021, one of the important introductions is the [prelude changes], which add
    /// `TryFrom`, `TryInto`, and `FromIterator` into the standard library's prelude. Since this
    /// results in an ambiguity as to which method/function to call when an existing `try_into`
    /// method is called via dot-call syntax or a `try_from`/`from_iter` associated function
    /// is called directly on a type.
    ///
    /// [prelude changes]: https://blog.rust-lang.org/inside-rust/2021/03/04/planning-rust-2021.html#prelude-changes
    pub RUST_2021_PRELUDE_COLLISIONS,
    Allow,
    "detects the usage of trait methods which are ambiguous with traits added to the \
        prelude in future editions",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/prelude.html>",
        reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
    };
}

declare_lint! {
    /// The `rust_2021_prefixes_incompatible_syntax` lint detects identifiers that will be parsed as a
    /// prefix instead in Rust 2021.
    ///
    /// ### Example
    ///
    /// ```rust,edition2018,compile_fail
    /// #![deny(rust_2021_prefixes_incompatible_syntax)]
    ///
    /// macro_rules! m {
    ///     (z $x:expr) => ();
    /// }
    ///
    /// m!(z"hey");
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In Rust 2015 and 2018, `z"hey"` is two tokens: the identifier `z`
    /// followed by the string literal `"hey"`. In Rust 2021, the `z` is
    /// considered a prefix for `"hey"`.
    ///
    /// This lint suggests to add whitespace between the `z` and `"hey"` tokens
    /// to keep them separated in Rust 2021.
    // Allow this lint -- rustdoc doesn't yet support threading edition into this lint's parser.
    #[allow(rustdoc::invalid_rust_codeblocks)]
    pub RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
    Allow,
    "identifiers that will be parsed as a prefix in Rust 2021",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/reserving-syntax.html>",
        reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
    };
    crate_level_only
}

declare_lint! {
    /// The `unsupported_calling_conventions` lint is output whenever there is a use of the
    /// `stdcall`, `fastcall`, `thiscall`, `vectorcall` calling conventions (or their unwind
    /// variants) on targets that cannot meaningfully be supported for the requested target.
    ///
    /// For example `stdcall` does not make much sense for a x86_64 or, more apparently, powerpc
    /// code, because this calling convention was never specified for those targets.
    ///
    /// Historically MSVC toolchains have fallen back to the regular C calling convention for
    /// targets other than x86, but Rust doesn't really see a similar need to introduce a similar
    /// hack across many more targets.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs specific targets)
    /// extern "stdcall" fn stdcall() {}
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: use of calling convention not supported on this target
    ///   --> $DIR/unsupported.rs:39:1
    ///    |
    /// LL | extern "stdcall" fn stdcall() {}
    ///    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ///    |
    ///    = note: `#[warn(unsupported_calling_conventions)]` on by default
    ///    = warning: this was previously accepted by the compiler but is being phased out;
    ///               it will become a hard error in a future release!
    ///    = note: for more information, see issue ...
    /// ```
    ///
    /// ### Explanation
    ///
    /// On most of the targets the behaviour of `stdcall` and similar calling conventions is not
    /// defined at all, but was previously accepted due to a bug in the implementation of the
    /// compiler.
    pub UNSUPPORTED_CALLING_CONVENTIONS,
    Warn,
    "use of unsupported calling convention",
    @future_incompatible = FutureIncompatibleInfo {
        reference: "issue #87678 <https://github.com/rust-lang/rust/issues/87678>",
    };
}

declare_lint! {
    /// The `break_with_label_and_loop` lint detects labeled `break` expressions with
    /// an unlabeled loop as their value expression.
    ///
    /// ### Example
    ///
    /// ```rust
    /// 'label: loop {
    ///     break 'label loop { break 42; };
    /// };
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In Rust, loops can have a label, and `break` expressions can refer to that label to
    /// break out of specific loops (and not necessarily the innermost one). `break` expressions
    /// can also carry a value expression, which can be another loop. A labeled `break` with an
    /// unlabeled loop as its value expression is easy to confuse with an unlabeled break with
    /// a labeled loop and is thus discouraged (but allowed for compatibility); use parentheses
    /// around the loop expression to silence this warning. Unlabeled `break` expressions with
    /// labeled loops yield a hard error, which can also be silenced by wrapping the expression
    /// in parentheses.
    pub BREAK_WITH_LABEL_AND_LOOP,
    Warn,
    "`break` expression with label and unlabeled loop as value expression"
}

declare_lint! {
    /// The `non_exhaustive_omitted_patterns` lint detects when a wildcard (`_` or `..`) in a
    /// pattern for a `#[non_exhaustive]` struct or enum is reachable.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs separate crate)
    /// // crate A
    /// #[non_exhaustive]
    /// pub enum Bar {
    ///     A,
    ///     B, // added variant in non breaking change
    /// }
    ///
    /// // in crate B
    /// #![feature(non_exhaustive_omitted_patterns_lint)]
    ///
    /// match Bar::A {
    ///     Bar::A => {},
    ///     #[warn(non_exhaustive_omitted_patterns)]
    ///     _ => {},
    /// }
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: reachable patterns not covered of non exhaustive enum
    ///    --> $DIR/reachable-patterns.rs:70:9
    ///    |
    /// LL |         _ => {}
    ///    |         ^ pattern `B` not covered
    ///    |
    ///  note: the lint level is defined here
    ///   --> $DIR/reachable-patterns.rs:69:16
    ///    |
    /// LL |         #[warn(non_exhaustive_omitted_patterns)]
    ///    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ///    = help: ensure that all possible cases are being handled by adding the suggested match arms
    ///    = note: the matched value is of type `Bar` and the `non_exhaustive_omitted_patterns` attribute was found
    /// ```
    ///
    /// ### Explanation
    ///
    /// Structs and enums tagged with `#[non_exhaustive]` force the user to add a
    /// (potentially redundant) wildcard when pattern-matching, to allow for future
    /// addition of fields or variants. The `non_exhaustive_omitted_patterns` lint
    /// detects when such a wildcard happens to actually catch some fields/variants.
    /// In other words, when the match without the wildcard would not be exhaustive.
    /// This lets the user be informed if new fields/variants were added.
    pub NON_EXHAUSTIVE_OMITTED_PATTERNS,
    Allow,
    "detect when patterns of types marked `non_exhaustive` are missed",
    @feature_gate = sym::non_exhaustive_omitted_patterns_lint;
}

declare_lint! {
    /// The `text_direction_codepoint_in_comment` lint detects Unicode codepoints in comments that
    /// change the visual representation of text on screen in a way that does not correspond to
    /// their on memory representation.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(text_direction_codepoint_in_comment)]
    /// fn main() {
    ///     println!("{:?}"); // '‮');
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Unicode allows changing the visual flow of text on screen in order to support scripts that
    /// are written right-to-left, but a specially crafted comment can make code that will be
    /// compiled appear to be part of a comment, depending on the software used to read the code.
    /// To avoid potential problems or confusion, such as in CVE-2021-42574, by default we deny
    /// their use.
    pub TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
    Deny,
    "invisible directionality-changing codepoints in comment"
}

declare_lint! {
    /// The `duplicate_macro_attributes` lint detects when a `#[test]`-like built-in macro
    /// attribute is duplicated on an item. This lint may trigger on `bench`, `cfg_eval`, `test`
    /// and `test_case`.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (needs --test)
    /// #[test]
    /// #[test]
    /// fn foo() {}
    /// ```
    ///
    /// This will produce:
    ///
    /// ```text
    /// warning: duplicated attribute
    ///  --> src/lib.rs:2:1
    ///   |
    /// 2 | #[test]
    ///   | ^^^^^^^
    ///   |
    ///   = note: `#[warn(duplicate_macro_attributes)]` on by default
    /// ```
    ///
    /// ### Explanation
    ///
    /// A duplicated attribute may erroneously originate from a copy-paste and the effect of it
    /// being duplicated may not be obvious or desirable.
    ///
    /// For instance, doubling the `#[test]` attributes registers the test to be run twice with no
    /// change to its environment.
    ///
    /// [issue #90979]: https://github.com/rust-lang/rust/issues/90979
    pub DUPLICATE_MACRO_ATTRIBUTES,
    Warn,
    "duplicated attribute"
}

declare_lint! {
    /// The `suspicious_auto_trait_impls` lint checks for potentially incorrect
    /// implementations of auto traits.
    ///
    /// ### Example
    ///
    /// ```rust
    /// struct Foo<T>(T);
    ///
    /// unsafe impl<T> Send for Foo<*const T> {}
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// A type can implement auto traits, e.g. `Send`, `Sync` and `Unpin`,
    /// in two different ways: either by writing an explicit impl or if
    /// all fields of the type implement that auto trait.
    ///
    /// The compiler disables the automatic implementation if an explicit one
    /// exists for given type constructor. The exact rules governing this
    /// are currently unsound, quite subtle, and will be modified in the future.
    /// This change will cause the automatic implementation to be disabled in more
    /// cases, potentially breaking some code.
    pub SUSPICIOUS_AUTO_TRAIT_IMPLS,
    Warn,
    "the rules governing auto traits will change in the future",
    @future_incompatible = FutureIncompatibleInfo {
        reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
        reference: "issue #93367 <https://github.com/rust-lang/rust/issues/93367>",
    };
}

declare_lint! {
    /// The `deprecated_where_clause_location` lint detects when a where clause in front of the equals
    /// in an associated type.
    ///
    /// ### Example
    ///
    /// ```rust
    /// trait Trait {
    ///   type Assoc<'a> where Self: 'a;
    /// }
    ///
    /// impl Trait for () {
    ///   type Assoc<'a> where Self: 'a = ();
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// The preferred location for where clauses on associated types in impls
    /// is after the type. However, for most of generic associated types development,
    /// it was only accepted before the equals. To provide a transition period and
    /// further evaluate this change, both are currently accepted. At some point in
    /// the future, this may be disallowed at an edition boundary; but, that is
    /// undecided currently.
    pub DEPRECATED_WHERE_CLAUSE_LOCATION,
    Warn,
    "deprecated where clause location"
}

declare_lint! {
    /// The `test_unstable_lint` lint tests unstable lints and is perma-unstable.
    ///
    /// ### Example
    ///
    /// ```rust
    /// #![allow(test_unstable_lint)]
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// In order to test the behavior of unstable lints, a permanently-unstable
    /// lint is required. This lint can be used to trigger warnings and errors
    /// from the compiler related to unstable lints.
    pub TEST_UNSTABLE_LINT,
    Deny,
    "this unstable lint is only for testing",
    @feature_gate = sym::test_unstable_lint;
}

declare_lint! {
    /// The `ffi_unwind_calls` lint detects calls to foreign functions or function pointers with
    /// `C-unwind` or other FFI-unwind ABIs.
    ///
    /// ### Example
    ///
    /// ```rust,ignore (need FFI)
    /// #![feature(ffi_unwind_calls)]
    /// #![feature(c_unwind)]
    ///
    /// # mod impl {
    /// #     #[no_mangle]
    /// #     pub fn "C-unwind" fn foo() {}
    /// # }
    ///
    /// extern "C-unwind" {
    ///     fn foo();
    /// }
    ///
    /// fn bar() {
    ///     unsafe { foo(); }
    ///     let ptr: unsafe extern "C-unwind" fn() = foo;
    ///     unsafe { ptr(); }
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// For crates containing such calls, if they are compiled with `-C panic=unwind` then the
    /// produced library cannot be linked with crates compiled with `-C panic=abort`. For crates
    /// that desire this ability it is therefore necessary to avoid such calls.
    pub FFI_UNWIND_CALLS,
    Allow,
    "call to foreign functions or function pointers with FFI-unwind ABI",
    @feature_gate = sym::c_unwind;
}

declare_lint! {
    /// The `named_arguments_used_positionally` lint detects cases where named arguments are only
    /// used positionally in format strings. This usage is valid but potentially very confusing.
    ///
    /// ### Example
    ///
    /// ```rust,compile_fail
    /// #![deny(named_arguments_used_positionally)]
    /// fn main() {
    ///     let _x = 5;
    ///     println!("{}", _x = 1); // Prints 1, will trigger lint
    ///
    ///     println!("{}", _x); // Prints 5, no lint emitted
    ///     println!("{_x}", _x = _x); // Prints 5, no lint emitted
    /// }
    /// ```
    ///
    /// {{produces}}
    ///
    /// ### Explanation
    ///
    /// Rust formatting strings can refer to named arguments by their position, but this usage is
    /// potentially confusing. In particular, readers can incorrectly assume that the declaration
    /// of named arguments is an assignment (which would produce the unit type).
    /// For backwards compatibility, this is not a hard error.
    pub NAMED_ARGUMENTS_USED_POSITIONALLY,
    Warn,
    "named arguments in format used positionally"
}