Auto merge of #60669 - c410-f3r:attrs-fn, r=petrochenkov

Allow attributes in formal function parameters

Implements https://github.com/rust-lang/rust/issues/60406.

This is my first contribution to the compiler and since this is a large and complex project, I am not fully aware of the consequences of the changes I have made.

**TODO**

- [x] Forbid some built-in attributes.
- [x] Expand cfg/cfg_attr

2 files changed, 8 insertions, 2 deletions

diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 2a03e49996b..9d4bf7d518d 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -963,9 +963,10 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     fn arg(&self, span: Span, ident: ast::Ident, ty: P<ast::Ty>) -> ast::Arg {
         let arg_pat = self.pat_ident(span, ident);
         ast::Arg {
-            ty,
+            attrs: ThinVec::default(),
+            id: ast::DUMMY_NODE_ID,
             pat: arg_pat,
-            id: ast::DUMMY_NODE_ID
+            ty,
         }
     }
 
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 084d4fd3820..3fa96c60bff 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -1578,6 +1578,11 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
             *id = self.cx.resolver.next_node_id()
         }
     }
+
+    fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
+        self.cfg.configure_fn_decl(&mut fn_decl);
+        noop_visit_fn_decl(fn_decl, self);
+    }
 }
 
 pub struct ExpansionConfig<'feat> {