Add feature gate for unnamed_fields

Author: jedel1043

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -300,6 +300,21 @@ impl<'a> PostExpansionVisitor<'a> {
 }
 
 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
+    fn visit_field_def(&mut self, s: &'a ast::FieldDef) {
+        match s.variant {
+            ast::FieldVariant::Unnamed(_) => {
+                gate_feature_post!(
+                    &self,
+                    unnamed_fields,
+                    s.span,
+                    "unnamed fields are not yet fully implemented"
+                )
+            }
+            _ => {}
+        }
+        visit::walk_field_def(self, s);
+    }
+
     fn visit_attribute(&mut self, attr: &ast::Attribute) {
         let attr_info =
             attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name)).map(|a| **a);
@@ -692,6 +707,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
         gate_all!(destructuring_assignment, "destructuring assignments are unstable");
     }
     gate_all!(pub_macro_rules, "`pub` on `macro_rules` items is unstable");
+    gate_all!(unnamed_fields, "unnamed fields are not yet fully implemented");
 
     // All uses of `gate_all!` below this point were added in #65742,
     // and subsequently disabled (with the non-early gating readded).

compiler/rustc_feature/src/active.rs

@@ -642,6 +642,9 @@ declare_features! (
     /// Allows `extern "wasm" fn`
     (active, wasm_abi, "1.53.0", Some(83788), None),
 
+    /// Allows unnamed fields of struct and union type
+    (active, unnamed_fields, "1.53.0", Some(49804), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------
@@ -669,6 +672,7 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::const_generics_defaults,
     sym::inherent_associated_types,
     sym::type_alias_impl_trait,
+    sym::unnamed_fields,
 ];
 
 /// Some features are not allowed to be used together at the same time, if

compiler/rustc_span/src/symbol.rs

@@ -1254,6 +1254,7 @@ symbols! {
         unix,
         unlikely,
         unmarked_api,
+        unnamed_fields,
         unpin,
         unreachable,
         unreachable_code,

src/test/ui/feature-gates/feature-gate-unnamed_fields.rs

@@ -0,0 +1,16 @@
+struct Foo {
+    _: struct { //~ ERROR unnamed fields are not yet fully implemented
+        foo: u8
+    }
+}
+
+union Bar {
+    _: union { //~ ERROR unnamed fields are not yet fully implemented
+        bar: u8
+    }
+}
+
+struct S;
+struct Baz {
+    _: S //~ ERROR unnamed fields are not yet fully implemented
+}