lint won't trigger for trait impls

Author: clueless-skywatcher

clippy_lints/src/unused_underscore_prefixed_argument.rs

@@ -1,4 +1,5 @@
 use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::is_trait_impl_item;
 use clippy_utils::visitors::is_local_used;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::FnKind;
@@ -68,6 +69,10 @@ impl<'tcx> LateLintPass<'tcx> for UnusedUnderscorePrefixedArgument {
                 if ctx.effective_visibilities.is_exported(def_id) {
                     return;
                 }
+                let hir_id = ctx.tcx.local_def_id_to_hir_id(def_id);
+                if is_trait_impl_item(ctx, hir_id) {
+                    return;
+                }
                 for param in body.params {
                     if let PatKind::Binding(_, hir_id, name, _) = param.pat.kind
                         && name.as_str().starts_with('_')

tests/ui/unused_underscore_prefixed_argument.rs

@@ -32,4 +32,14 @@ impl PrivStruct {
     // Will still raise lint because this is within a private struct
 }
 
+pub trait Abc {
+    fn abc(a: i32, _b: i32);
+}
+
+pub struct Def;
+
+impl Abc for Def {
+    fn abc(a: i32, _b: i32) {}
+}
+
 fn main() {}