When deriveing, account for HRTB on BareFn fields

estebank · estebank · commit e7ad2da7f134 · 2024-06-04T20:46:03.000Z
When given ```rust trait SomeTrait { type SomeType<'a>; } struct Foo<T: SomeTrait> { x: for<'a> fn(T::SomeType<'a>) } ``` expand to ```rust impl<T: ::core::clone::Clone + SomeTrait> ::core::clone::Clone for Foo<T> where for<'a> T::SomeType<'a>: ::core::clone::Clone { #[inline] fn clone(&self) -> Foo<T> { Foo { x: ::core::clone::Clone::clone(&self.x) } } } ``` instead of the previous invalid ``` impl<T: ::core::clone::Clone + SomeTrait> ::core::clone::Clone for Foo<T> where T::SomeType<'a>: ::core::clone::Clone { #[inline] fn clone(&self) -> Foo<T> { Foo { x: ::core::clone::Clone::clone(&self.x) } } } ``` Fix #122622.
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -412,6 +412,15 @@ fn find_type_parameters(
 
     impl<'a, 'b> visit::Visitor<'a> for Visitor<'a, 'b> {
         fn visit_ty(&mut self, ty: &'a ast::Ty) {
+            let stack_len = self.bound_generic_params_stack.len();
+            if let ast::TyKind::BareFn(bare_fn) = &ty.kind
+                && !bare_fn.generic_params.is_empty()
+            {
+                // Given a field `x: for<'a> fn(T::SomeType<'a>)`, we wan't to account for `'a` so
+                // that we generate `where for<'a> T::SomeType<'a>: ::core::clone::Clone`. #122622
+                self.bound_generic_params_stack.extend(bare_fn.generic_params.iter().cloned());
+            }
+
             if let ast::TyKind::Path(_, path) = &ty.kind
                 && let Some(segment) = path.segments.first()
                 && self.ty_param_names.contains(&segment.ident.name)
@@ -422,7 +431,8 @@ fn find_type_parameters(
                 });
             }
 
-            visit::walk_ty(self, ty)
+            visit::walk_ty(self, ty);
+            self.bound_generic_params_stack.truncate(stack_len);
         }
 
         // Place bound generic params on a stack, to extract them when a type is encountered.
diff --git a/tests/ui/derives/derive-hrtb-for-bare-fn-field-with-lifetime.rs b/tests/ui/derives/derive-hrtb-for-bare-fn-field-with-lifetime.rs
@@ -0,0 +1,13 @@
+//@ run-pass
+// Issue #122622: `#[derive(Clone)]` should work for HRTB function type taking an associated type
+#![allow(dead_code)]
+trait SomeTrait {
+    type SomeType<'a>;
+}
+
+#[derive(Clone)]
+struct Foo<T: SomeTrait> {
+    x: for<'a> fn(T::SomeType<'a>)
+}
+
+fn main() {}
