Implement lint for inherent to_string() method.

CHANGELOG.md

@@ -973,6 +973,8 @@ Released 2018-09-13
 [`ineffective_bit_mask`]: https://rust-lang.github.io/rust-clippy/master/index.html#ineffective_bit_mask
 [`infallible_destructuring_match`]: https://rust-lang.github.io/rust-clippy/master/index.html#infallible_destructuring_match
 [`infinite_iter`]: https://rust-lang.github.io/rust-clippy/master/index.html#infinite_iter
+[`inherent_to_string`]: https://rust-lang.github.io/rust-clippy/master/index.html#inherent_to_string
+[`inherent_to_string_shadow_display`]: https://rust-lang.github.io/rust-clippy/master/index.html#inherent_to_string_shadow_display
 [`inline_always`]: https://rust-lang.github.io/rust-clippy/master/index.html#inline_always
 [`inline_fn_without_body`]: https://rust-lang.github.io/rust-clippy/master/index.html#inline_fn_without_body
 [`int_plus_one`]: https://rust-lang.github.io/rust-clippy/master/index.html#int_plus_one

README.md

@@ -6,7 +6,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are 306 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 308 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 

clippy_lints/src/inherent_to_string.rs

@@ -0,0 +1,154 @@
+use if_chain::if_chain;
+use rustc::hir::{ImplItem, ImplItemKind};
+use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
+use rustc::{declare_lint_pass, declare_tool_lint};
+
+use crate::utils::{
+ get_trait_def_id, implements_trait, in_macro_or_desugar, match_type, paths, return_ty, span_help_and_lint,
+ trait_ref_of_method, walk_ptrs_ty,
+};
+
+declare_clippy_lint! {
+ /// **What id does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String`.
+ ///
+ /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. As the functionality of `Display` is much more versatile, it should be preferred.
+ ///
+ /// **Known problems:** None
+ ///
+ /// ** Example:**
+ ///
+ /// ```rust
+ /// // Bad
+ /// pub struct A;
+ ///
+ /// impl A {
+ /// pub fn to_string(&self) -> String {
+ /// "I am A".to_string()
+ /// }
+ /// }
+ /// ```
+ ///
+ /// ```rust
+ /// // Good
+ /// use std::fmt;
+ ///
+ /// pub struct A;
+ ///
+ /// impl fmt::Display for A {
+ /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ /// write!(f, "I am A")
+ /// }
+ /// }
+ /// ```
+ pub INHERENT_TO_STRING,
+ style,
+ "type implements inherent method `to_string()`, but should instead implement the `Display` trait"
+}
+
+declare_clippy_lint! {
+ /// **What id does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String` and if the type implementing this method also implements the `Display` trait.
+ ///
+ /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. The less versatile inherent method will then shadow the implementation introduced by `Display`.
+ ///
+ /// **Known problems:** None
+ ///
+ /// ** Example:**
+ ///
+ /// ```rust
+ /// // Bad
+ /// use std::fmt;
+ ///
+ /// pub struct A;
+ ///
+ /// impl A {
+ /// pub fn to_string(&self) -> String {
+ /// "I am A".to_string()
+ /// }
+ /// }
+ ///
+ /// impl fmt::Display for A {
+ /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ /// write!(f, "I am A, too")
+ /// }
+ /// }
+ /// ```
+ ///
+ /// ```rust
+ /// // Good
+ /// use std::fmt;
+ ///
+ /// pub struct A;
+ ///
+ /// impl fmt::Display for A {
+ /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ /// write!(f, "I am A")
+ /// }
+ /// }
+ /// ```
+ pub INHERENT_TO_STRING_SHADOW_DISPLAY,
+ correctness,
+ "type implements inherent method `to_string()`, which gets shadowed by the implementation of the `Display` trait "
+}
+
+declare_lint_pass!(InherentToString => [INHERENT_TO_STRING, INHERENT_TO_STRING_SHADOW_DISPLAY]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InherentToString {
+ fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx ImplItem) {
+ if in_macro_or_desugar(impl_item.span) {
+ return;
+ }
+
+ if_chain! {
+ // Check if item is a method, called to_string and has a parameter 'self'
+ if let ImplItemKind::Method(ref signature, _) = impl_item.node;
+ if impl_item.ident.name.as_str() == "to_string";
+ let decl = &signature.decl;
+ if decl.implicit_self.has_implicit_self();
+
+ // Check if return type is String
+ if match_type(cx, return_ty(cx, impl_item.hir_id), &paths::STRING);
+
+ // Filters instances of to_string which are required by a trait
+ if trait_ref_of_method(cx, impl_item.hir_id).is_none();
+
+ then {
+ show_lint(cx, impl_item);
+ }
+ }
+ }
+}
+
+fn show_lint(cx: &LateContext<'_, '_>, item: &ImplItem) {
+ let display_trait_id =
+ get_trait_def_id(cx, &["core", "fmt", "Display"]).expect("Failed to get trait ID of `Display`!");
+
+ // Get the real type of 'self'
+ let fn_def_id = cx.tcx.hir().local_def_id(item.hir_id);
+ let self_type = cx.tcx.fn_sig(fn_def_id).input(0);
+ let self_type = walk_ptrs_ty(self_type.skip_binder());
+
+ // Emit either a warning or an error
+ if implements_trait(cx, self_type, display_trait_id, &[]) {
+ span_help_and_lint(
+ cx,
+ INHERENT_TO_STRING_SHADOW_DISPLAY,
+ item.span,
+ &format!(
+ "type `{}` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`",
+ self_type.to_string()
+ ),
+ &format!("remove the inherent method from type `{}`", self_type.to_string())
+ );
+ } else {
+ span_help_and_lint(
+ cx,
+ INHERENT_TO_STRING,
+ item.span,
+ &format!(
+ "implementation of inherent method `to_string(&self) -> String` for type `{}`",
+ self_type.to_string()
+ ),
+ &format!("implement trait `Display` for type `{}` instead", self_type.to_string()),
+ );
+ }
+}

clippy_lints/src/lib.rs

@@ -195,6 +195,7 @@ pub mod indexing_slicing;
 pub mod infallible_destructuring_match;
 pub mod infinite_iter;
 pub mod inherent_impl;
+pub mod inherent_to_string;
 pub mod inline_fn_without_body;
 pub mod int_plus_one;
 pub mod integer_division;
@@ -585,6 +586,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
  reg.register_late_lint_pass(box path_buf_push_overwrite::PathBufPushOverwrite);
  reg.register_late_lint_pass(box checked_conversions::CheckedConversions);
  reg.register_late_lint_pass(box integer_division::IntegerDivision);
+ reg.register_late_lint_pass(box inherent_to_string::InherentToString);
 
  reg.register_lint_group("clippy::restriction", Some("clippy_restriction"), vec![
  arithmetic::FLOAT_ARITHMETIC,
@@ -725,6 +727,8 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
  indexing_slicing::OUT_OF_BOUNDS_INDEXING,
  infallible_destructuring_match::INFALLIBLE_DESTRUCTURING_MATCH,
  infinite_iter::INFINITE_ITER,
+ inherent_to_string::INHERENT_TO_STRING,
+ inherent_to_string::INHERENT_TO_STRING_SHADOW_DISPLAY,
  inline_fn_without_body::INLINE_FN_WITHOUT_BODY,
  int_plus_one::INT_PLUS_ONE,
  invalid_ref::INVALID_REF,
@@ -913,6 +917,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
  formatting::SUSPICIOUS_ASSIGNMENT_FORMATTING,
  formatting::SUSPICIOUS_ELSE_FORMATTING,
  infallible_destructuring_match::INFALLIBLE_DESTRUCTURING_MATCH,
+ inherent_to_string::INHERENT_TO_STRING,
  len_zero::LEN_WITHOUT_IS_EMPTY,
  len_zero::LEN_ZERO,
  let_if_seq::USELESS_LET_IF_SEQ,
@@ -1075,6 +1080,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
  functions::NOT_UNSAFE_PTR_ARG_DEREF,
  indexing_slicing::OUT_OF_BOUNDS_INDEXING,
  infinite_iter::INFINITE_ITER,
+ inherent_to_string::INHERENT_TO_STRING_SHADOW_DISPLAY,
  inline_fn_without_body::INLINE_FN_WITHOUT_BODY,
  invalid_ref::INVALID_REF,
  literal_representation::MISTYPED_LITERAL_SUFFIXES,

src/lintlist/mod.rs

@@ -6,7 +6,7 @@ pub use lint::Lint;
 pub use lint::LINT_LEVELS;
 
 // begin lint list, do not remove this comment, it’s used in `update_lints`
-pub const ALL_LINTS: [Lint; 306] = [
+pub const ALL_LINTS: [Lint; 308] = [
  Lint {
  name: "absurd_extreme_comparisons",
  group: "correctness",
@@ -728,6 +728,20 @@ pub const ALL_LINTS: [Lint; 306] = [
  deprecation: None,
  module: "infinite_iter",
  },
+ Lint {
+ name: "inherent_to_string",
+ group: "style",
+ desc: "type implements inherent method `to_string()`, but should instead implement the `Display` trait",
+ deprecation: None,
+ module: "inherent_to_string",
+ },
+ Lint {
+ name: "inherent_to_string_shadow_display",
+ group: "correctness",
+ desc: "type implements inherent method `to_string()`, which gets shadowed by the implementation of the `Display` trait ",
+ deprecation: None,
+ module: "inherent_to_string",
+ },
  Lint {
  name: "inline_always",
  group: "pedantic",

tests/ui/inherent_to_string.rs

@@ -0,0 +1,84 @@
+#![warn(clippy::inherent_to_string)]
+#![deny(clippy::inherent_to_string_shadow_display)]
+
+use std::fmt;
+
+trait FalsePositive {
+ fn to_string(&self) -> String;
+}
+
+struct A;
+struct B;
+struct C;
+struct D;
+struct E;
+
+impl A {
+ // Should be detected; emit warning
+ fn to_string(&self) -> String {
+ "A.to_string()".to_string()
+ }
+
+ // Should not be detected as it does not match the function signature
+ fn to_str(&self) -> String {
+ "A.to_str()".to_string()
+ }
+}
+
+// Should not be detected as it is a free function
+fn to_string() -> String {
+ "free to_string()".to_string()
+}
+
+impl B {
+ // Should not be detected, wrong return type
+ fn to_string(&self) -> i32 {
+ 42
+ }
+}
+
+impl C {
+ // Should be detected and emit error as C also implements Display
+ fn to_string(&self) -> String {
+ "C.to_string()".to_string()
+ }
+}
+
+impl fmt::Display for C {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ write!(f, "impl Display for C")
+ }
+}
+
+impl FalsePositive for D {
+ // Should not be detected, as it is a trait function
+ fn to_string(&self) -> String {
+ "impl FalsePositive for D".to_string()
+ }
+}
+
+impl E {
+ // Should not be detected, as it is not bound to an instance
+ fn to_string() -> String {
+ "E::to_string()".to_string()
+ }
+}
+
+fn main() {
+ let a = A;
+ a.to_string();
+ a.to_str();
+
+ to_string();
+
+ let b = B;
+ b.to_string();
+
+ let c = C;
+ C.to_string();
+
+ let d = D;
+ d.to_string();
+
+ E::to_string();
+}

tests/ui/inherent_to_string.stderr

@@ -0,0 +1,28 @@
+error: implementation of inherent method `to_string(&self) -> String` for type `A`
+ --> $DIR/inherent_to_string.rs:18:5
+ |
+LL | / fn to_string(&self) -> String {
+LL | | "A.to_string()".to_string()
+LL | | }
+ | |_____^
+ |
+ = note: `-D clippy::inherent-to-string` implied by `-D warnings`
+ = help: implement trait `Display` for type `A` instead
+
+error: type `C` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`
+ --> $DIR/inherent_to_string.rs:42:5
+ |
+LL | / fn to_string(&self) -> String {
+LL | | "C.to_string()".to_string()
+LL | | }
+ | |_____^
+ |
+note: lint level defined here
+ --> $DIR/inherent_to_string.rs:2:9
+ |
+LL | #![deny(clippy::inherent_to_string_shadow_display)]
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ = help: remove the inherent method from type `C`
+
+error: aborting due to 2 previous errors
+