Add new multiple_bound_locations lint

CHANGELOG.md

@@ -5430,6 +5430,7 @@ Released 2018-09-13
 [`modulo_arithmetic`]: https://rust-lang.github.io/rust-clippy/master/index.html#modulo_arithmetic
 [`modulo_one`]: https://rust-lang.github.io/rust-clippy/master/index.html#modulo_one
 [`multi_assignments`]: https://rust-lang.github.io/rust-clippy/master/index.html#multi_assignments
+[`multiple_bound_locations`]: https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations
 [`multiple_crate_versions`]: https://rust-lang.github.io/rust-clippy/master/index.html#multiple_crate_versions
 [`multiple_inherent_impl`]: https://rust-lang.github.io/rust-clippy/master/index.html#multiple_inherent_impl
 [`multiple_unsafe_ops_per_block`]: https://rust-lang.github.io/rust-clippy/master/index.html#multiple_unsafe_ops_per_block

clippy_lints/src/declared_lints.rs

@@ -498,6 +498,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::module_style::MOD_MODULE_FILES_INFO,
     crate::module_style::SELF_NAMED_MODULE_FILES_INFO,
     crate::multi_assignments::MULTI_ASSIGNMENTS_INFO,
+    crate::multiple_bound_locations::MULTIPLE_BOUND_LOCATIONS_INFO,
     crate::multiple_unsafe_ops_per_block::MULTIPLE_UNSAFE_OPS_PER_BLOCK_INFO,
     crate::mut_key::MUTABLE_KEY_TYPE_INFO,
     crate::mut_mut::MUT_MUT_INFO,

clippy_lints/src/lib.rs

@@ -226,6 +226,7 @@ mod missing_trait_methods;
 mod mixed_read_write_in_expression;
 mod module_style;
 mod multi_assignments;
+mod multiple_bound_locations;
 mod multiple_unsafe_ops_per_block;
 mod mut_key;
 mod mut_mut;
@@ -1111,6 +1112,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     });
     store.register_late_pass(move |_| Box::new(incompatible_msrv::IncompatibleMsrv::new(msrv())));
     store.register_late_pass(|_| Box::new(to_string_trait_impl::ToStringTraitImpl));
+    store.register_early_pass(|| Box::new(multiple_bound_locations::MultipleBoundLocations));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/multiple_bound_locations.rs

@@ -0,0 +1,84 @@
+use rustc_ast::visit::FnKind;
+use rustc_ast::{NodeId, WherePredicate};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::source::snippet_opt;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Check if a generic is defined both in the bound predicate and in the `where` clause.
+    ///
+    /// ### Why is this bad?
+    /// It can be confusing for developers when seeing bounds for a generic in multiple places.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// fn ty<F: std::fmt::Debug>(a: F)
+    /// where
+    ///     F: Sized,
+    /// {}
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// fn ty<F>(a: F)
+    /// where
+    ///     F: Sized + std::fmt::Debug,
+    /// {}
+    /// ```
+    #[clippy::version = "1.77.0"]
+    pub MULTIPLE_BOUND_LOCATIONS,
+    suspicious,
+    "defining generic bounds in multiple locations"
+}
+
+declare_lint_pass!(MultipleBoundLocations => [MULTIPLE_BOUND_LOCATIONS]);
+
+impl EarlyLintPass for MultipleBoundLocations {
+    fn check_fn(&mut self, cx: &EarlyContext<'_>, kind: FnKind<'_>, _: Span, _: NodeId) {
+        if let FnKind::Fn(_, _, _, _, generics, _) = kind
+            && !generics.params.is_empty()
+            && !generics.where_clause.predicates.is_empty()
+        {
+            let mut generic_params_with_bounds = FxHashMap::default();
+
+            for param in &generics.params {
+                if !param.bounds.is_empty() {
+                    generic_params_with_bounds.insert(param.ident.name.as_str(), param.ident.span);
+                }
+            }
+            for clause in &generics.where_clause.predicates {
+                match clause {
+                    WherePredicate::BoundPredicate(pred) => {
+                        if (!pred.bound_generic_params.is_empty() || !pred.bounds.is_empty())
+                            && let Some(name) = snippet_opt(cx, pred.bounded_ty.span)
+                            && let Some(bound_span) = generic_params_with_bounds.get(name.as_str())
+                        {
+                            emit_lint(cx, *bound_span, pred.bounded_ty.span);
+                        }
+                    },
+                    WherePredicate::RegionPredicate(pred) => {
+                        if !pred.bounds.is_empty()
+                            && let Some(bound_span) = generic_params_with_bounds.get(&pred.lifetime.ident.name.as_str())
+                        {
+                            emit_lint(cx, *bound_span, pred.lifetime.ident.span);
+                        }
+                    },
+                    WherePredicate::EqPredicate(_) => {},
+                }
+            }
+        }
+    }
+}
+
+fn emit_lint(cx: &EarlyContext<'_>, bound_span: Span, where_span: Span) {
+    span_lint(
+        cx,
+        MULTIPLE_BOUND_LOCATIONS,
+        vec![bound_span, where_span],
+        "bound is defined in more than one place",
+    );
+}

tests/ui/multiple_bound_locations.rs

@@ -0,0 +1,60 @@
+#![warn(clippy::multiple_bound_locations)]
+
+fn ty<F: std::fmt::Debug>(a: F)
+//~^ ERROR: bound is defined in more than one place
+where
+    F: Sized,
+{
+}
+
+fn lifetime<'a, 'b: 'a, 'c>(a: &'b str, b: &'a str, c: &'c str)
+//~^ ERROR: bound is defined in more than one place
+where
+    'b: 'c,
+{
+}
+
+fn ty_pred<F: Sized>()
+//~^ ERROR: bound is defined in more than one place
+where
+    for<'a> F: Send + 'a,
+{
+}
+
+struct B;
+
+impl B {
+    fn ty<F: std::fmt::Debug>(a: F)
+    //~^ ERROR: bound is defined in more than one place
+    where
+        F: Sized,
+    {
+    }
+
+    fn lifetime<'a, 'b: 'a, 'c>(a: &'b str, b: &'a str, c: &'c str)
+    //~^ ERROR: bound is defined in more than one place
+    where
+        'b: 'c,
+    {
+    }
+
+    fn ty_pred<F: Sized>()
+    //~^ ERROR: bound is defined in more than one place
+    where
+        for<'a> F: Send + 'a,
+    {
+    }
+}
+
+struct C<F>(F);
+
+impl<F> C<F> {
+    fn foo(_f: F) -> Self
+    where
+        F: std::fmt::Display,
+    {
+        todo!()
+    }
+}
+
+fn main() {}

tests/ui/multiple_bound_locations.stderr

@@ -0,0 +1,59 @@
+error: bound is defined in more than one place
+  --> tests/ui/multiple_bound_locations.rs:3:7
+   |
+LL | fn ty<F: std::fmt::Debug>(a: F)
+   |       ^
+...
+LL |     F: Sized,
+   |     ^
+   |
+   = note: `-D clippy::multiple-bound-locations` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::multiple_bound_locations)]`
+
+error: bound is defined in more than one place
+  --> tests/ui/multiple_bound_locations.rs:10:17
+   |
+LL | fn lifetime<'a, 'b: 'a, 'c>(a: &'b str, b: &'a str, c: &'c str)
+   |                 ^^
+...
+LL |     'b: 'c,
+   |     ^^
+
+error: bound is defined in more than one place
+  --> tests/ui/multiple_bound_locations.rs:17:12
+   |
+LL | fn ty_pred<F: Sized>()
+   |            ^
+...
+LL |     for<'a> F: Send + 'a,
+   |             ^
+
+error: bound is defined in more than one place
+  --> tests/ui/multiple_bound_locations.rs:27:11
+   |
+LL |     fn ty<F: std::fmt::Debug>(a: F)
+   |           ^
+...
+LL |         F: Sized,
+   |         ^
+
+error: bound is defined in more than one place
+  --> tests/ui/multiple_bound_locations.rs:34:21
+   |
+LL |     fn lifetime<'a, 'b: 'a, 'c>(a: &'b str, b: &'a str, c: &'c str)
+   |                     ^^
+...
+LL |         'b: 'c,
+   |         ^^
+
+error: bound is defined in more than one place
+  --> tests/ui/multiple_bound_locations.rs:41:16
+   |
+LL |     fn ty_pred<F: Sized>()
+   |                ^
+...
+LL |         for<'a> F: Send + 'a,
+   |                 ^
+
+error: aborting due to 6 previous errors
+

tests/ui/trait_duplication_in_bounds_unfixable.rs

@@ -1,4 +1,5 @@
 #![deny(clippy::trait_duplication_in_bounds)]
+#![allow(clippy::multiple_bound_locations)]
 
 use std::collections::BTreeMap;
 use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};

tests/ui/trait_duplication_in_bounds_unfixable.stderr

@@ -1,5 +1,5 @@
 error: this trait bound is already specified in the where clause
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:6:15
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:7:15
    |
 LL | fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
    |               ^^^^^
@@ -12,55 +12,55 @@ LL | #![deny(clippy::trait_duplication_in_bounds)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: this trait bound is already specified in the where clause
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:6:23
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:7:23
    |
 LL | fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
    |                       ^^^^^^^
    |
    = help: consider removing this trait bound
 
 error: this trait bound is already specified in trait declaration
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:37:15
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:38:15
    |
 LL |         Self: Default;
    |               ^^^^^^^
    |
    = help: consider removing this trait bound
 
 error: this trait bound is already specified in trait declaration
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:52:15
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:53:15
    |
 LL |         Self: Default + Clone;
    |               ^^^^^^^
    |
    = help: consider removing this trait bound
 
 error: this trait bound is already specified in trait declaration
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:59:15
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:60:15
    |
 LL |         Self: Default + Clone;
    |               ^^^^^^^
    |
    = help: consider removing this trait bound
 
 error: this trait bound is already specified in trait declaration
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:59:25
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:60:25
    |
 LL |         Self: Default + Clone;
    |                         ^^^^^
    |
    = help: consider removing this trait bound
 
 error: this trait bound is already specified in trait declaration
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:64:15
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:65:15
    |
 LL |         Self: Default;
    |               ^^^^^^^
    |
    = help: consider removing this trait bound
 
 error: this trait bound is already specified in trait declaration
-  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:100:15
+  --> tests/ui/trait_duplication_in_bounds_unfixable.rs:101:15
    |
 LL |         Self: Iterator<Item = Foo>,
    |               ^^^^^^^^^^^^^^^^^^^^

tests/ui/type_repetition_in_bounds.rs

@@ -1,5 +1,5 @@
 #![deny(clippy::type_repetition_in_bounds)]
-#![allow(clippy::extra_unused_type_parameters)]
+#![allow(clippy::extra_unused_type_parameters, clippy::multiple_bound_locations)]
 
 use serde::Deserialize;
 use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};

tests/ui/unnecessary_cast.fixed

@@ -2,6 +2,7 @@
 #![warn(clippy::unnecessary_cast)]
 #![allow(
     clippy::borrow_as_ptr,
+    clippy::multiple_bound_locations,
     clippy::no_effect,
     clippy::nonstandard_macro_braces,
     clippy::unnecessary_operation,

tests/ui/unnecessary_cast.rs

@@ -2,6 +2,7 @@
 #![warn(clippy::unnecessary_cast)]
 #![allow(
     clippy::borrow_as_ptr,
+    clippy::multiple_bound_locations,
     clippy::no_effect,
     clippy::nonstandard_macro_braces,
     clippy::unnecessary_operation,