From 478555d468d54105a0202220b7632b08a992b9be Mon Sep 17 00:00:00 2001
From: John Kelly <johnharrykelly@gmail.com>
Date: Sun, 30 Apr 2023 13:16:04 +0100
Subject: [PATCH] wip

---
 clippy_lints/src/trait_bounds.rs        | 45 +++++++++++++++++++++++--
 tests/ui/trait_duplication_in_bounds.rs |  8 +++++
 2 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/clippy_lints/src/trait_bounds.rs b/clippy_lints/src/trait_bounds.rs
index b5f11b4ac..13651c978 100644
--- a/clippy_lints/src/trait_bounds.rs
+++ b/clippy_lints/src/trait_bounds.rs
@@ -9,7 +9,7 @@ use rustc_data_structures::unhash::UnhashMap;
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
 use rustc_hir::{
-    GenericArg, GenericBound, Generics, Item, ItemKind, Node, Path, PathSegment, PredicateOrigin, QPath,
+    GenericArg, GenericBound, Generics, Item, ItemKind, MutTy, Node, Path, PathSegment, PredicateOrigin, QPath,
     TraitBoundModifier, TraitItem, TraitRef, Ty, TyKind, WherePredicate,
 };
 use rustc_lint::{LateContext, LateLintPass};
@@ -37,12 +37,12 @@ declare_clippy_lint! {
     #[clippy::version = "1.38.0"]
     pub TYPE_REPETITION_IN_BOUNDS,
     nursery,
-    "types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
+    "types are repeated unnecessarily 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
+    /// Checks for cases where generics or trait objects are being used and multiple
     /// syntax specifications for trait bounds are used simultaneously.
     ///
     /// ### Why is this bad?
@@ -167,6 +167,45 @@ impl<'tcx> LateLintPass<'tcx> for TraitBounds {
             }
         }
     }
+
+    fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx Ty<'tcx>) {
+        let TyKind::Ref(
+            ..,
+            MutTy {
+                ty: Ty {
+                    kind: TyKind::TraitObject(
+                        bounds,
+                        ..
+                    ),
+                    ..
+                },
+                ..
+            }
+        ) = ty.kind else { return; };
+
+        if bounds.len() < 2 {
+            return;
+        }
+
+        let mut seen_def_ids = FxHashSet::default();
+
+        for bound in bounds.iter() {
+            let Some(def_id) = bound.trait_ref.trait_def_id() else { continue; };
+
+            let already_seen = !seen_def_ids.insert(def_id);
+
+            if already_seen {
+                span_lint_and_help(
+                    cx,
+                    TRAIT_DUPLICATION_IN_BOUNDS,
+                    bound.span,
+                    "this trait bound is already specified in trait declaration",
+                    None,
+                    "consider removing this trait bound",
+                );
+            }
+        }
+    }
 }
 
 impl TraitBounds {
diff --git a/tests/ui/trait_duplication_in_bounds.rs b/tests/ui/trait_duplication_in_bounds.rs
index a7a1caf28..f4f4a9fcb 100644
--- a/tests/ui/trait_duplication_in_bounds.rs
+++ b/tests/ui/trait_duplication_in_bounds.rs
@@ -109,4 +109,12 @@ fn qualified_path<T: std::clone::Clone + Clone + foo::Clone>(arg0: T) {
     unimplemented!();
 }
 
+fn good_trait_object(arg0: &(dyn Any + Send)) {
+    unimplemented!();
+}
+
+fn bad_trait_object(arg0: &(dyn Any + Send + Send)) {
+    unimplemented!();
+}
+
 fn main() {}