Don't lint on impls for now

Author: botahamec

clippy_lints/src/unnecessary_box_returns.rs

@@ -46,11 +46,10 @@ impl LateLintPass<'_> for UnnecessaryBoxReturns {
         _: Span,
         _: HirId,
     ) {
-        // it's unclear what part of a closure you would span, so for now it's ignored
-        // if this is changed, please also make sure not to call `hir_ty_to_ty` below
-        if matches!(fn_kind, FnKind::Closure) {
-            return;
-        }
+        // It's unclear what part of a closure you would span, so for now it's ignored.
+        // Trait implementations should also not be linted.
+        // If this is changed, please also make sure not to call `hir_ty_to_ty` below.
+        let FnKind::ItemFn(..) = fn_kind else { return };
 
         let FnRetTy::Return(return_ty_hir) = &decl.output else { return };
 

tests/ui/unnecessary_box_returns.rs

@@ -1,7 +1,18 @@
 #![warn(clippy::unnecessary_box_returns)]
 
+trait Bar {
+    fn baz(&self) -> Box<usize>;
+}
+
 struct Foo {}
 
+impl Bar for Foo {
+    // don't lint: this is a problem with the trait, not the implementation
+    fn baz(&self) -> Box<usize> {
+        Box::new(42)
+    }
+}
+
 // lint
 fn boxed_usize() -> Box<usize> {
     Box::new(5)

tests/ui/unnecessary_box_returns.stderr

@@ -1,13 +1,13 @@
 error: function returns `Box<usize>` when `usize` implements `Sized`
-  --> $DIR/unnecessary_box_returns.rs:6:21
+  --> $DIR/unnecessary_box_returns.rs:17:21
    |
 LL | fn boxed_usize() -> Box<usize> {
    |                     ^^^^^^^^^^ help: change the return type to: `usize`
    |
    = note: `-D clippy::unnecessary-box-returns` implied by `-D warnings`
 
 error: function returns `Box<Foo>` when `Foo` implements `Sized`
-  --> $DIR/unnecessary_box_returns.rs:11:19
+  --> $DIR/unnecessary_box_returns.rs:22:19
    |
 LL | fn boxed_foo() -> Box<Foo> {
    |                   ^^^^^^^^ help: change the return type to: `Foo`