Auto merge of #130337 - BoxyUwU:anon_const_macro_call, r=camelid

Fix anon const def-creation when macros are involved take 2

Fixes #130321

There were two cases that #129137 did not handle correctly:

- Given a const argument `Foo<{ bar!() }>` in which `bar!()` expands to `N`, we would visit the anon const and then visit the `{ bar() }` expression instead of visiting the macro call. This meant that we would build a def for the anon const as `{ bar!() }` is not a trivial const argument as `bar!()` is not a path.
- Given a const argument `Foo<{ bar!() }>` is which `bar!()` expands to `{ qux!() }` in which `qux!()` expands to `N`, it should not be considered a trivial const argument as `{{ N }}` has two pairs of braces.  If we only looked at `qux`'s expansion it would *look* like a trivial const argument even though it is not. We have to track whether we have "unwrapped" a brace already when recursing into the expansions of `bar`/`qux`/any macro

r? `@camelid`

1 files changed, 6 insertions, 5 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index ac65b7b22bc..d49265de202 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1187,8 +1187,8 @@ impl Expr {
     /// `min_const_generics` as more complex expressions are not supported.
     ///
     /// Does not ensure that the path resolves to a const param, the caller should check this.
-    pub fn is_potential_trivial_const_arg(&self) -> bool {
-        let this = self.maybe_unwrap_block();
+    pub fn is_potential_trivial_const_arg(&self, strip_identity_block: bool) -> bool {
+        let this = if strip_identity_block { self.maybe_unwrap_block().1 } else { self };
 
         if let ExprKind::Path(None, path) = &this.kind
             && path.is_potential_trivial_const_arg()
@@ -1199,14 +1199,15 @@ impl Expr {
         }
     }
 
-    pub fn maybe_unwrap_block(&self) -> &Expr {
+    /// Returns an expression with (when possible) *one* outter brace removed
+    pub fn maybe_unwrap_block(&self) -> (bool, &Expr) {
         if let ExprKind::Block(block, None) = &self.kind
             && let [stmt] = block.stmts.as_slice()
             && let StmtKind::Expr(expr) = &stmt.kind
         {
-            expr
+            (true, expr)
         } else {
-            self
+            (false, self)
         }
     }