From 84f8caca9c975bca4b46172b0bad5e5fef81bb61 Mon Sep 17 00:00:00 2001
From: Jason Newcomb <jsnewcomb@pm.me>
Date: Thu, 15 Apr 2021 12:20:43 -0400
Subject: [PATCH] Don't lint `multiple_inherent_impl` with generic arguments

---
 clippy_lints/src/inherent_impl.rs | 27 +++++++++++++++++++++------
 tests/ui/impl.rs                  | 17 +++++++++++++++++
 2 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/clippy_lints/src/inherent_impl.rs b/clippy_lints/src/inherent_impl.rs
index c31013e49be5..f3095849b0d5 100644
--- a/clippy_lints/src/inherent_impl.rs
+++ b/clippy_lints/src/inherent_impl.rs
@@ -3,7 +3,7 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::in_macro;
 use rustc_hir::def_id::DefIdMap;
-use rustc_hir::{def_id, Crate, Impl, Item, ItemKind};
+use rustc_hir::{def_id, Crate, Impl, Item, ItemKind, QPath, TyKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::Span;
@@ -53,15 +53,30 @@ impl<'tcx> LateLintPass<'tcx> for MultipleInherentImpl {
         if let ItemKind::Impl(Impl {
             ref generics,
             of_trait: None,
+            self_ty,
             ..
         }) = item.kind
         {
-            // Remember for each inherent implementation encountered its span and generics
-            // but filter out implementations that have generic params (type or lifetime)
-            // or are derived from a macro
-            if !in_macro(item.span) && generics.params.is_empty() {
-                self.impls.insert(item.def_id.to_def_id(), item.span);
+            // Don't count impls from macros, or with generic parameters.
+            if in_macro(item.span) || !generics.params.is_empty() {
+                return;
             }
+            match self_ty.kind {
+                TyKind::OpaqueDef(_, []) => (),
+                TyKind::Path(QPath::Resolved(None, path)) if path.segments.iter().all(|s| s.args.is_none()) => (),
+                TyKind::TraitObject(traits, ..)
+                    if traits.iter().all(|t| {
+                        t.bound_generic_params.is_empty() && t.trait_ref.path.segments.iter().all(|s| s.args.is_none())
+                    }) =>
+                {
+                    ()
+                },
+                // Don't count impls with generic arguments.
+                _ => return,
+            }
+
+            // Remember the span of each inherent implementation encountered
+            self.impls.insert(item.def_id.to_def_id(), item.span);
         }
     }
 
diff --git a/tests/ui/impl.rs b/tests/ui/impl.rs
index 1c46e3a53378..d721031ee640 100644
--- a/tests/ui/impl.rs
+++ b/tests/ui/impl.rs
@@ -33,4 +33,21 @@ impl fmt::Debug for MyStruct {
     }
 }
 
+// issue #5772
+struct WithArgs<T>(T);
+impl WithArgs<u32> {
+    fn f1() {}
+}
+impl WithArgs<u64> {
+    fn f2() {}
+}
+
+trait TraitWithArgs<T> {}
+impl dyn TraitWithArgs<u32> {
+    fn f1(&self) {}
+}
+impl dyn TraitWithArgs<u64> {
+    fn f2(&self) {}
+}
+
 fn main() {}