Auto merge of #5852 - wiomoc:feature/lint-duplicate-trait, r=Manishearth

Add lint for duplicate methods of trait bounds

rel: #5777

changelog: Add [`trait_duplication_in_bounds`] lint

CHANGELOG.md

@@ -1723,6 +1723,7 @@ Released 2018-09-13
 [`too_many_arguments`]: https://rust-lang.github.io/rust-clippy/master/index.html#too_many_arguments
 [`too_many_lines`]: https://rust-lang.github.io/rust-clippy/master/index.html#too_many_lines
 [`toplevel_ref_arg`]: https://rust-lang.github.io/rust-clippy/master/index.html#toplevel_ref_arg
+[`trait_duplication_in_bounds`]: https://rust-lang.github.io/rust-clippy/master/index.html#trait_duplication_in_bounds
 [`transmute_bytes_to_str`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_bytes_to_str
 [`transmute_float_to_int`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_float_to_int
 [`transmute_int_to_bool`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_int_to_bool

clippy_lints/src/lib.rs

@@ -786,6 +786,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
  &tabs_in_doc_comments::TABS_IN_DOC_COMMENTS,
  &temporary_assignment::TEMPORARY_ASSIGNMENT,
  &to_digit_is_some::TO_DIGIT_IS_SOME,
+ &trait_bounds::TRAIT_DUPLICATION_IN_BOUNDS,
  &trait_bounds::TYPE_REPETITION_IN_BOUNDS,
  &transmute::CROSSPOINTER_TRANSMUTE,
  &transmute::TRANSMUTE_BYTES_TO_STR,
@@ -1174,6 +1175,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
  LintId::of(&ranges::RANGE_PLUS_ONE),
  LintId::of(&shadow::SHADOW_UNRELATED),
  LintId::of(&strings::STRING_ADD_ASSIGN),
+ LintId::of(&trait_bounds::TRAIT_DUPLICATION_IN_BOUNDS),
  LintId::of(&trait_bounds::TYPE_REPETITION_IN_BOUNDS),
  LintId::of(&trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF),
  LintId::of(&types::CAST_LOSSLESS),

clippy_lints/src/trait_bounds.rs

@@ -2,9 +2,10 @@ use crate::utils::{in_macro, snippet, snippet_with_applicability, span_lint_and_
 use if_chain::if_chain;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::Applicability;
-use rustc_hir::{GenericBound, Generics, WherePredicate};
+use rustc_hir::{def::Res, GenericBound, Generics, ParamName, Path, QPath, TyKind, WherePredicate};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::Span;
 
 declare_clippy_lint! {
  /// **What it does:** This lint warns about unnecessary type repetitions in trait bounds
@@ -29,6 +30,35 @@ declare_clippy_lint! {
  "Types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
 }
 
+declare_clippy_lint! {
+ /// **What it does:** Checks for cases where generics are being used and multiple
+ /// syntax specifications for trait bounds are used simultaneously.
+ ///
+ /// **Why is this bad?** Duplicate bounds makes the code
+ /// less readable than specifing them only once.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ /// ```rust
+ /// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
+ /// ```
+ ///
+ /// Could be written as:
+ ///
+ /// ```rust
+ /// fn func<T: Clone + Default>(arg: T) {}
+ /// ```
+ /// or
+ /// ///
+ /// ```rust
+ /// fn func<T>(arg: T) where T: Clone + Default {}
+ /// ```
+ pub TRAIT_DUPLICATION_IN_BOUNDS,
+ pedantic,
+ "Check if the same trait bounds are specified twice during a function declaration"
+}
+
 #[derive(Copy, Clone)]
 pub struct TraitBounds {
  max_trait_bounds: u64,
@@ -41,10 +71,25 @@ impl TraitBounds {
  }
 }
 
-impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS]);
+impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
 
 impl<'tcx> LateLintPass<'tcx> for TraitBounds {
  fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
+ self.check_type_repetition(cx, gen);
+ check_trait_bound_duplication(cx, gen);
+ }
+}
+
+fn get_trait_res_span_from_bound(bound: &GenericBound<'_>) -> Option<(Res, Span)> {
+ if let GenericBound::Trait(t, _) = bound {
+ Some((t.trait_ref.path.res, t.span))
+ } else {
+ None
+ }
+}
+
+impl TraitBounds {
+ fn check_type_repetition(self, cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
  if in_macro(gen.span) {
  return;
  }
@@ -101,3 +146,48 @@ impl<'tcx> LateLintPass<'tcx> for TraitBounds {
  }
  }
 }
+
+fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
+ if in_macro(gen.span) || gen.params.is_empty() || gen.where_clause.predicates.is_empty() {
+ return;
+ }
+
+ let mut map = FxHashMap::default();
+ for param in gen.params {
+ if let ParamName::Plain(ref ident) = param.name {
+ let res = param
+ .bounds
+ .iter()
+ .filter_map(get_trait_res_span_from_bound)
+ .collect::<Vec<_>>();
+ map.insert(*ident, res);
+ }
+ }
+
+ for predicate in gen.where_clause.predicates {
+ if_chain! {
+ if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
+ if !in_macro(bound_predicate.span);
+ if let TyKind::Path(ref path) = bound_predicate.bounded_ty.kind;
+ if let QPath::Resolved(_, Path { ref segments, .. }) = path;
+ if let Some(segment) = segments.first();
+ if let Some(trait_resolutions_direct) = map.get(&segment.ident);
+ then {
+ for (res_where, _) in bound_predicate.bounds.iter().filter_map(get_trait_res_span_from_bound) {
+ if let Some((_, span_direct)) = trait_resolutions_direct
+ .iter()
+ .find(|(res_direct, _)| *res_direct == res_where) {
+ span_lint_and_help(
+ cx,
+ TRAIT_DUPLICATION_IN_BOUNDS,
+ *span_direct,
+ "this trait bound is already specified in the where clause",
+ None,
+ "consider removing this trait bound",
+ );
+ }
+ }
+ }
+ }
+ }
+}

src/lintlist/mod.rs

@@ -2166,6 +2166,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
  deprecation: None,
  module: "misc",
  },
+ Lint {
+ name: "trait_duplication_in_bounds",
+ group: "pedantic",
+ desc: "Check if the same trait bounds are specified twice during a function declaration",
+ deprecation: None,
+ module: "trait_bounds",
+ },
  Lint {
  name: "transmute_bytes_to_str",
  group: "complexity",

tests/ui/trait_duplication_in_bounds.rs

@@ -0,0 +1,31 @@
+#![deny(clippy::trait_duplication_in_bounds)]
+
+use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};
+
+fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
+where
+ T: Clone,
+ T: Default,
+{
+ unimplemented!();
+}
+
+fn good_bar<T: Clone + Default>(arg: T) {
+ unimplemented!();
+}
+
+fn good_foo<T>(arg: T)
+where
+ T: Clone + Default,
+{
+ unimplemented!();
+}
+
+fn good_foobar<T: Default>(arg: T)
+where
+ T: Clone,
+{
+ unimplemented!();
+}
+
+fn main() {}

tests/ui/trait_duplication_in_bounds.stderr

@@ -0,0 +1,23 @@
+error: this trait bound is already specified in the where clause
+ --> $DIR/trait_duplication_in_bounds.rs:5:15
+ |
+LL | fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
+ | ^^^^^
+ |
+note: the lint level is defined here
+ --> $DIR/trait_duplication_in_bounds.rs:1:9
+ |
+LL | #![deny(clippy::trait_duplication_in_bounds)]
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ = help: consider removing this trait bound
+
+error: this trait bound is already specified in the where clause
+ --> $DIR/trait_duplication_in_bounds.rs:5:23
+ |
+LL | fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
+ | ^^^^^^^
+ |
+ = help: consider removing this trait bound
+
+error: aborting due to 2 previous errors
+