Rollup of 3 pull requests

compiler/rustc_ast_lowering/src/path.rs

@@ -34,7 +34,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         modifiers: Option<ast::TraitBoundModifiers>,
     ) -> hir::QPath<'hir> {
         let qself_position = qself.as_ref().map(|q| q.position);
-        let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx));
+        let qself = qself
+            .as_ref()
+            // Reject cases like `<impl Trait>::Assoc` and `<impl Trait as Trait>::Assoc`.
+            .map(|q| self.lower_ty(&q.ty, ImplTraitContext::Disallowed(ImplTraitPosition::Path)));
 
         let partial_res =
             self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
@@ -75,6 +78,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             None
         };
 
+        // Only permit `impl Trait` in the final segment. E.g., we permit `Option<impl Trait>`,
+        // `option::Option<T>::Xyz<impl Trait>` and reject `option::Option<impl Trait>::Xyz`.
+        let itctx = |i| {
+            if i + 1 == p.segments.len() {
+                itctx
+            } else {
+                ImplTraitContext::Disallowed(ImplTraitPosition::Path)
+            }
+        };
+
         let path_span_lo = p.span.shrink_to_lo();
         let proj_start = p.segments.len() - unresolved_segments;
         let path = self.arena.alloc(hir::Path {
@@ -121,7 +134,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         segment,
                         param_mode,
                         generic_args_mode,
-                        itctx,
+                        itctx(i),
                         bound_modifier_allowed_features.clone(),
                     )
                 },
@@ -185,7 +198,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 segment,
                 param_mode,
                 generic_args_mode,
-                itctx,
+                itctx(i),
                 None,
             ));
             let qpath = hir::QPath::TypeRelative(ty, hir_segment);

compiler/rustc_ast_passes/messages.ftl

@@ -146,8 +146,6 @@ ast_passes_generic_before_constraints = generic arguments must come before the f
 
 ast_passes_generic_default_trailing = generic parameters with a default must be trailing
 
-ast_passes_impl_trait_path = `impl Trait` is not allowed in path parameters
-
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
     .help = remove one of these features
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -80,10 +80,6 @@ struct AstValidator<'a> {
 
     disallow_tilde_const: Option<TildeConstReason>,
 
-    /// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
-    /// or `Foo::Bar<impl Trait>`
-    is_impl_trait_banned: bool,
-
     /// Used to ban explicit safety on foreign items when the extern block is not marked as unsafe.
     extern_mod_safety: Option<Safety>,
 
@@ -123,12 +119,6 @@ impl<'a> AstValidator<'a> {
         self.extern_mod_safety = old;
     }
 
-    fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
-        let old = mem::replace(&mut self.is_impl_trait_banned, true);
-        f(self);
-        self.is_impl_trait_banned = old;
-    }
-
     fn with_tilde_const(
         &mut self,
         disallowed: Option<TildeConstReason>,
@@ -213,37 +203,6 @@ impl<'a> AstValidator<'a> {
                 .with_tilde_const(Some(TildeConstReason::TraitObject), |this| {
                     visit::walk_ty(this, t)
                 }),
-            TyKind::Path(qself, path) => {
-                // We allow these:
-                //  - `Option<impl Trait>`
-                //  - `option::Option<impl Trait>`
-                //  - `option::Option<T>::Foo<impl Trait>`
-                //
-                // But not these:
-                //  - `<impl Trait>::Foo`
-                //  - `option::Option<impl Trait>::Foo`.
-                //
-                // To implement this, we disallow `impl Trait` from `qself`
-                // (for cases like `<impl Trait>::Foo>`)
-                // but we allow `impl Trait` in `GenericArgs`
-                // iff there are no more PathSegments.
-                if let Some(qself) = qself {
-                    // `impl Trait` in `qself` is always illegal
-                    self.with_banned_impl_trait(|this| this.visit_ty(&qself.ty));
-                }
-
-                // Note that there should be a call to visit_path here,
-                // so if any logic is added to process `Path`s a call to it should be
-                // added both in visit_path and here. This code mirrors visit::walk_path.
-                for (i, segment) in path.segments.iter().enumerate() {
-                    // Allow `impl Trait` iff we're on the final path segment
-                    if i == path.segments.len() - 1 {
-                        self.visit_path_segment(segment);
-                    } else {
-                        self.with_banned_impl_trait(|this| this.visit_path_segment(segment));
-                    }
-                }
-            }
             _ => visit::walk_ty(self, t),
         }
     }
@@ -737,10 +696,6 @@ impl<'a> AstValidator<'a> {
                 }
             }
             TyKind::ImplTrait(_, bounds) => {
-                if self.is_impl_trait_banned {
-                    self.dcx().emit_err(errors::ImplTraitPath { span: ty.span });
-                }
-
                 if let Some(outer_impl_trait_sp) = self.outer_impl_trait {
                     self.dcx().emit_err(errors::NestedImplTrait {
                         span: ty.span,
@@ -1729,7 +1684,6 @@ pub fn check_crate(
         has_proc_macro_decls: false,
         outer_impl_trait: None,
         disallow_tilde_const: Some(TildeConstReason::Item),
-        is_impl_trait_banned: false,
         extern_mod_safety: None,
         lint_buffer: lints,
     };

compiler/rustc_ast_passes/src/errors.rs

@@ -418,13 +418,6 @@ pub(crate) struct TraitObjectBound {
     pub span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(ast_passes_impl_trait_path, code = E0667)]
-pub(crate) struct ImplTraitPath {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(ast_passes_nested_impl_trait, code = E0666)]
 pub(crate) struct NestedImplTrait {

compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs → compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs

@@ -19,7 +19,7 @@ macro_rules! path {
     ($span:expr, $($part:ident)::*) => { vec![$(Ident::new(sym::$part, $span),)*] }
 }
 
-pub(crate) fn expand_deriving_smart_ptr(
+pub(crate) fn expand_deriving_coerce_pointee(
     cx: &ExtCtxt<'_>,
     span: Span,
     _mitem: &MetaItem,
@@ -41,7 +41,7 @@ pub(crate) fn expand_deriving_smart_ptr(
             cx.dcx()
                 .struct_span_err(
                     span,
-                    "`SmartPointer` can only be derived on `struct`s with `#[repr(transparent)]`",
+                    "`CoercePointee` can only be derived on `struct`s with `#[repr(transparent)]`",
                 )
                 .emit();
             return;
@@ -54,7 +54,7 @@ pub(crate) fn expand_deriving_smart_ptr(
             cx.dcx()
                 .struct_span_err(
                     span,
-                    "`SmartPointer` can only be derived on `struct`s with at least one field",
+                    "`CoercePointee` can only be derived on `struct`s with at least one field",
                 )
                 .emit();
             return;
@@ -64,7 +64,7 @@ pub(crate) fn expand_deriving_smart_ptr(
         cx.dcx()
             .struct_span_err(
                 span,
-                "`SmartPointer` can only be derived on `struct`s with `#[repr(transparent)]`",
+                "`CoercePointee` can only be derived on `struct`s with `#[repr(transparent)]`",
             )
             .emit();
         return;
@@ -94,10 +94,10 @@ pub(crate) fn expand_deriving_smart_ptr(
         .collect();
 
     let pointee_param_idx = if type_params.is_empty() {
-        // `#[derive(SmartPointer)]` requires at least one generic type on the target `struct`
+        // `#[derive(CoercePointee)]` requires at least one generic type on the target `struct`
         cx.dcx().struct_span_err(
             span,
-            "`SmartPointer` can only be derived on `struct`s that are generic over at least one type",
+            "`CoercePointee` can only be derived on `struct`s that are generic over at least one type",
         ).emit();
         return;
     } else if type_params.len() == 1 {
@@ -113,15 +113,15 @@ pub(crate) fn expand_deriving_smart_ptr(
             (None, _) => {
                 cx.dcx().struct_span_err(
                     span,
-                    "exactly one generic type parameter must be marked as #[pointee] to derive SmartPointer traits",
+                    "exactly one generic type parameter must be marked as #[pointee] to derive CoercePointee traits",
                 ).emit();
                 return;
             }
             (Some((_, one)), Some((_, another))) => {
                 cx.dcx()
                     .struct_span_err(
                         vec![one, another],
-                        "only one type parameter can be marked as `#[pointee]` when deriving SmartPointer traits",
+                        "only one type parameter can be marked as `#[pointee]` when deriving CoercePointee traits",
                     )
                     .emit();
                 return;
@@ -185,7 +185,7 @@ pub(crate) fn expand_deriving_smart_ptr(
                 .struct_span_err(
                     pointee_ty_ident.span,
                     format!(
-                        "`derive(SmartPointer)` requires {} to be marked `?Sized`",
+                        "`derive(CoercePointee)` requires {} to be marked `?Sized`",
                         pointee_ty_ident.name
                     ),
                 )
@@ -195,7 +195,7 @@ pub(crate) fn expand_deriving_smart_ptr(
         let arg = GenericArg::Type(s_ty.clone());
         let unsize = cx.path_all(span, true, path!(span, core::marker::Unsize), vec![arg]);
         pointee.bounds.push(cx.trait_bound(unsize, false));
-        // Drop `#[pointee]` attribute since it should not be recognized outside `derive(SmartPointer)`
+        // Drop `#[pointee]` attribute since it should not be recognized outside `derive(CoercePointee)`
         pointee.attrs.retain(|attr| !attr.has_name(sym::pointee));
     }
 

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -22,12 +22,12 @@ macro path_std($($x:tt)*) {
 
 pub(crate) mod bounds;
 pub(crate) mod clone;
+pub(crate) mod coerce_pointee;
 pub(crate) mod debug;
 pub(crate) mod decodable;
 pub(crate) mod default;
 pub(crate) mod encodable;
 pub(crate) mod hash;
-pub(crate) mod smart_ptr;
 
 #[path = "cmp/eq.rs"]
 pub(crate) mod eq;

compiler/rustc_builtin_macros/src/lib.rs

@@ -133,7 +133,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
         PartialOrd: partial_ord::expand_deriving_partial_ord,
         RustcDecodable: decodable::expand_deriving_rustc_decodable,
         RustcEncodable: encodable::expand_deriving_rustc_encodable,
-        SmartPointer: smart_ptr::expand_deriving_smart_ptr,
+        CoercePointee: coerce_pointee::expand_deriving_coerce_pointee,
     }
 
     let client = proc_macro::bridge::client::Client::expand1(proc_macro::quote);

compiler/rustc_error_codes/src/error_codes/E0667.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 `impl Trait` is not allowed in path parameters.
 
 Erroneous code example:
 
-```compile_fail,E0667
+```ignore (removed error code)
 fn some_fn(mut x: impl Iterator) -> <impl Iterator>::Item { // error!
     x.next().unwrap()
 }
@@ -11,7 +13,7 @@ fn some_fn(mut x: impl Iterator) -> <impl Iterator>::Item { // error!
 You cannot use `impl Trait` in path parameters. If you want something
 equivalent, you can do this instead:
 
-```
+```ignore (removed error code)
 fn some_fn<T: Iterator>(mut x: T) -> T::Item { // ok!
     x.next().unwrap()
 }

compiler/rustc_feature/src/removed.rs

@@ -85,6 +85,8 @@ declare_features! (
     /// Allows default type parameters to influence type inference.
     (removed, default_type_parameter_fallback, "1.82.0", Some(27336),
      Some("never properly implemented; requires significant design work")),
+    /// Allows deriving traits as per `SmartPointer` specification
+    (removed, derive_smart_pointer, "1.79.0", Some(123430), Some("replaced by `CoercePointee`")),
     /// Allows using `#[doc(keyword = "...")]`.
     (removed, doc_keyword, "1.28.0", Some(51315),
      Some("merged into `#![feature(rustdoc_internals)]`")),

compiler/rustc_feature/src/unstable.rs

@@ -450,8 +450,6 @@ declare_features! (
     (unstable, deprecated_suggestion, "1.61.0", Some(94785)),
     /// Allows deref patterns.
     (incomplete, deref_patterns, "1.79.0", Some(87121)),
-    /// Allows deriving `SmartPointer` traits
-    (unstable, derive_smart_pointer, "1.79.0", Some(123430)),
     /// Controls errors in trait implementations.
     (unstable, do_not_recommend, "1.67.0", Some(51992)),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -1203,15 +1203,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     err.emit()
                 } else if let Err(reported) = qself_ty.error_reported() {
                     reported
-                } else if let ty::Alias(ty::Opaque, alias_ty) = qself_ty.kind() {
-                    // `<impl Trait as OtherTrait>::Assoc` makes no sense.
-                    struct_span_code_err!(
-                        self.dcx(),
-                        tcx.def_span(alias_ty.def_id),
-                        E0667,
-                        "`impl Trait` is not allowed in path parameters"
-                    )
-                    .emit() // Already reported in an earlier stage.
                 } else {
                     self.maybe_report_similar_assoc_fn(span, qself_ty, qself)?;
 

compiler/rustc_lint/src/builtin.rs

@@ -4,21 +4,14 @@
 //! AST visitor. Also see `rustc_session::lint::builtin`, which contains the
 //! definitions of lints that are emitted directly inside the main compiler.
 //!
-//! To add a new lint to rustc, declare it here using `declare_lint!()`.
+//! To add a new lint to rustc, declare it here using [`declare_lint!`].
 //! Then add code to emit the new lint in the appropriate circumstances.
-//! You can do that in an existing `LintPass` if it makes sense, or in a
-//! new `LintPass`, or using `Session::add_lint` elsewhere in the
-//! compiler. Only do the latter if the check can't be written cleanly as a
-//! `LintPass` (also, note that such lints will need to be defined in
-//! `rustc_session::lint::builtin`, not here).
 //!
-//! If you define a new `EarlyLintPass`, you will also need to add it to the
-//! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
-//! `lib.rs`. Use the former for unit-like structs and the latter for structs
-//! with a `pub fn new()`.
+//! If you define a new [`EarlyLintPass`], you will also need to add it to the
+//! [`crate::early_lint_methods!`] invocation in `lib.rs`.
 //!
-//! If you define a new `LateLintPass`, you will also need to add it to the
-//! `late_lint_methods!` invocation in `lib.rs`.
+//! If you define a new [`LateLintPass`], you will also need to add it to the
+//! [`crate::late_lint_methods!`] invocation in `lib.rs`.
 
 use std::fmt::Write;
 

compiler/rustc_lint/src/context.rs

@@ -1,18 +1,7 @@
-//! Implementation of lint checking.
+//! Basic types for managing and implementing lints.
 //!
-//! The lint checking is mostly consolidated into one pass which runs
-//! after all other analyses. Throughout compilation, lint warnings
-//! can be added via the `add_lint` method on the Session structure. This
-//! requires a span and an ID of the node that the lint is being added to. The
-//! lint isn't actually emitted at that time because it is unknown what the
-//! actual lint level at that location is.
-//!
-//! To actually emit lint warnings/errors, a separate pass is used.
-//! A context keeps track of the current state of all lint levels.
-//! Upon entering a node of the ast which can modify the lint settings, the
-//! previous lint state is pushed onto a stack and the ast is then recursed
-//! upon. As the ast is traversed, this keeps track of the current lint level
-//! for all lint attributes.
+//! See <https://rustc-dev-guide.rust-lang.org/diagnostics.html> for an
+//! overview of how lints are implemented.
 
 use std::cell::Cell;
 use std::{iter, slice};
@@ -52,9 +41,6 @@ type LateLintPassFactory =
     dyn for<'tcx> Fn(TyCtxt<'tcx>) -> LateLintPassObject<'tcx> + sync::DynSend + sync::DynSync;
 
 /// Information about the registered lints.
-///
-/// This is basically the subset of `Context` that we can
-/// build early in the compile pipeline.
 pub struct LintStore {
     /// Registered lints.
     lints: Vec<&'static Lint>,

compiler/rustc_lint/src/early.rs

@@ -1,18 +1,8 @@
-//! Implementation of lint checking.
+//! Implementation of the early lint pass.
 //!
-//! The lint checking is mostly consolidated into one pass which runs
-//! after all other analyses. Throughout compilation, lint warnings
-//! can be added via the `add_lint` method on the Session structure. This
-//! requires a span and an ID of the node that the lint is being added to. The
-//! lint isn't actually emitted at that time because it is unknown what the
-//! actual lint level at that location is.
-//!
-//! To actually emit lint warnings/errors, a separate pass is used.
-//! A context keeps track of the current state of all lint levels.
-//! Upon entering a node of the ast which can modify the lint settings, the
-//! previous lint state is pushed onto a stack and the ast is then recursed
-//! upon. As the ast is traversed, this keeps track of the current lint level
-//! for all lint attributes.
+//! The early lint pass works on AST nodes after macro expansion and name
+//! resolution, just before AST lowering. These lints are for purely
+//! syntactical lints.
 
 use rustc_ast::ptr::P;
 use rustc_ast::visit::{self as ast_visit, Visitor, walk_list};