Auto merge of #116116 - Nilstrieb:gate-all-__SECRET_INTERNALS_DO_NOT_…

…USE_OR_YOU_WILL_BE_FIRED, r=compiler-errors

Rename the legacy feature gating macro

It had a really confusing name by shadowing the previous name, which has
caused issues in the past where people added their new syntax in the
legacy location.

This makes it clear.

Also adds a comment about the return type notation gating, which confused me why it was here at first before `@compiler-errors` told me why.

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -578,25 +578,31 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
         }
     }
 
-    // All uses of `gate_all!` below this point were added in #65742,
+    // All uses of `gate_all_legacy_dont_use!` below this point were added in #65742,
     // and subsequently disabled (with the non-early gating readded).
     // We emit an early future-incompatible warning for these.
     // New syntax gates should go above here to get a hard error gate.
-    macro_rules! gate_all {
+    macro_rules! gate_all_legacy_dont_use {
         ($gate:ident, $msg:literal) => {
             for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
                 gate_feature_post!(future_incompatible; &visitor, $gate, *span, $msg);
             }
         };
     }
 
-    gate_all!(trait_alias, "trait aliases are experimental");
-    gate_all!(associated_type_bounds, "associated type bounds are unstable");
-    gate_all!(return_type_notation, "return type notation is experimental");
-    gate_all!(decl_macro, "`macro` is experimental");
-    gate_all!(box_patterns, "box pattern syntax is experimental");
-    gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
-    gate_all!(try_blocks, "`try` blocks are unstable");
+    gate_all_legacy_dont_use!(trait_alias, "trait aliases are experimental");
+    gate_all_legacy_dont_use!(associated_type_bounds, "associated type bounds are unstable");
+    // Despite being a new feature, `where T: Trait<Assoc(): Sized>`, which is RTN syntax now,
+    // used to be gated under associated_type_bounds, which are right above, so RTN needs to
+    // be too.
+    gate_all_legacy_dont_use!(return_type_notation, "return type notation is experimental");
+    gate_all_legacy_dont_use!(decl_macro, "`macro` is experimental");
+    gate_all_legacy_dont_use!(box_patterns, "box pattern syntax is experimental");
+    gate_all_legacy_dont_use!(
+        exclusive_range_pattern,
+        "exclusive range pattern syntax is experimental"
+    );
+    gate_all_legacy_dont_use!(try_blocks, "`try` blocks are unstable");
 
     visit::walk_crate(&mut visitor, krate);
 }