Auto merge of #61229 - Centril:stabilize-repr_align_enum, r=nagisa

Stabilize #![feature(repr_align_enum)] in Rust 1.37.0

On an `enum` item, you may now write:

```rust
#[repr(align(X))]
enum Foo {
    // ...
}
```

This has equivalent effects to first defining:

```rust
#[repr(align(X))]
struct AlignX<T>(T);
```

and then using `AlignX<Foo>` in `Foo`'s stead.

r? @nagisa

1 files changed, 3 insertions, 14 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 7119fd13fbb..bbb297e3c4f 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -551,9 +551,6 @@ declare_features! (
     // Allows using `#[optimize(X)]`.
     (active, optimize_attribute, "1.34.0", Some(54882), None),
 
-    // Allows using `#[repr(align(X))]` on enums.
-    (active, repr_align_enum, "1.34.0", Some(57996), None),
-
     // Allows using C-variadics.
     (active, c_variadic, "1.34.0", Some(44930), None),
 
@@ -843,6 +840,9 @@ declare_features! (
     (accepted, extern_crate_self, "1.34.0", Some(56409), None),
     // Allows arbitrary delimited token streams in non-macro attributes.
     (accepted, unrestricted_attribute_tokens, "1.34.0", Some(55208), None),
+    // Allows using `#[repr(align(X))]` on enums with equivalent semantics
+    // to wrapping an enum in a wrapper struct with `#[repr(align(X))]`.
+    (accepted, repr_align_enum, "1.37.0", Some(57996), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: accepted features
@@ -2033,17 +2033,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
 
-            ast::ItemKind::Enum(..) => {
-                for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
-                    for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
-                        if item.check_name(sym::align) {
-                            gate_feature_post!(&self, repr_align_enum, attr.span,
-                                               "`#[repr(align(x))]` on enums is experimental");
-                        }
-                    }
-                }
-            }
-
             ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
                 if polarity == ast::ImplPolarity::Negative {
                     gate_feature_post!(&self, optin_builtin_traits,