Auto merge of rust-lang#10189 - Alexendoo:copy-packed-struct, r=giraffate

expl_impl_clone_on_copy: ignore packed structs with type/const params

changelog: [`expl_impl_clone_on_copy`]: Ignore `#[repr(packed)]` structs with type or const paramaters

Fixes rust-lang#10188

A more involved solution that checks if any bound on the trait impl aren't present on the struct definition would be ideal, but I couldn't see a nice way to go about that

Author: bors

clippy_lints/src/derive.rs

@@ -14,8 +14,8 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::traits::Reveal;
 use rustc_middle::ty::{
-    self, Binder, BoundConstness, Clause, GenericParamDefKind, ImplPolarity, ParamEnv, PredicateKind, TraitPredicate,
-    Ty, TyCtxt,
+    self, Binder, BoundConstness, Clause, GenericArgKind, GenericParamDefKind, ImplPolarity, ParamEnv, PredicateKind,
+    TraitPredicate, Ty, TyCtxt,
 };
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
@@ -366,6 +366,15 @@ fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &h
     if ty_subs.types().any(|ty| !implements_trait(cx, ty, clone_id, &[])) {
         return;
     }
+    // `#[repr(packed)]` structs with type/const parameters can't derive `Clone`.
+    // https://github.com/rust-lang/rust-clippy/issues/10188
+    if ty_adt.repr().packed()
+        && ty_subs
+            .iter()
+            .any(|arg| matches!(arg.unpack(), GenericArgKind::Type(_) | GenericArgKind::Const(_)))
+    {
+        return;
+    }
 
     span_lint_and_note(
         cx,

tests/ui/derive.rs

@@ -85,4 +85,15 @@ impl<T: Clone, U> Clone for GenericRef<'_, T, U> {
     }
 }
 
+// https://github.com/rust-lang/rust-clippy/issues/10188
+#[repr(packed)]
+#[derive(Copy)]
+struct Packed<T>(T);
+
+impl<T: Copy> Clone for Packed<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
 fn main() {}