[Clang] disallow attributes after namespace identifier

clang/docs/ReleaseNotes.rst

@@ -553,6 +553,8 @@ Attribute Changes in Clang
 - Clang now permits the usage of the placement new operator in ``[[msvc::constexpr]]``
   context outside of the std namespace. (#GH74924)
 
+- Clang now disallows the use of attributes after the namespace name. (#GH121407)
+
 Improvements to Clang's diagnostics
 -----------------------------------
 

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -283,6 +283,8 @@ def err_unexpected_qualified_namespace_alias : Error<
   "namespace alias must be a single identifier">;
 def err_unexpected_nested_namespace_attribute : Error<
   "attributes cannot be specified on a nested namespace definition">;
+def err_attribute_after_namespace : Error<
+  "standard attributes cannot appear after the namespace name">;
 def err_inline_namespace_alias : Error<"namespace alias cannot be inline">;
 def err_namespace_nonnamespace_scope : Error<
   "namespaces can only be defined in global or namespace scope">;

clang/lib/Parse/ParseDeclCXX.cpp

@@ -81,7 +81,7 @@ Parser::DeclGroupPtrTy Parser::ParseNamespace(DeclaratorContext Context,
 
   ParsedAttributes attrs(AttrFactory);
 
-  auto ReadAttributes = [&] {
+  auto ReadAttributes = [&](bool TrailingAttrs) {
     bool MoreToParse;
     do {
       MoreToParse = false;
@@ -90,6 +90,9 @@ Parser::DeclGroupPtrTy Parser::ParseNamespace(DeclaratorContext Context,
         MoreToParse = true;
       }
       if (getLangOpts().CPlusPlus11 && isCXX11AttributeSpecifier()) {
+        if (TrailingAttrs)
+          Diag(Tok.getLocation(), diag::err_attribute_after_namespace);
+
         Diag(Tok.getLocation(), getLangOpts().CPlusPlus17
                                     ? diag::warn_cxx14_compat_ns_enum_attribute
                                     : diag::ext_ns_enum_attribute)
@@ -100,7 +103,7 @@ Parser::DeclGroupPtrTy Parser::ParseNamespace(DeclaratorContext Context,
     } while (MoreToParse);
   };
 
-  ReadAttributes();
+  ReadAttributes(/*TrailingAttrs*/ false);
 
   if (Tok.is(tok::identifier)) {
     Ident = Tok.getIdentifierInfo();
@@ -126,7 +129,7 @@ Parser::DeclGroupPtrTy Parser::ParseNamespace(DeclaratorContext Context,
     }
   }
 
-  ReadAttributes();
+  ReadAttributes(/*TrailingAttrs*/ true);
 
   SourceLocation attrLoc = attrs.Range.getBegin();
 

clang/test/Parser/namespace-attributes.cpp

@@ -16,26 +16,26 @@ namespace [[]] __attribute__(()) A
 {
 }
 
-namespace A __attribute__(()) [[]]
+namespace A __attribute__(()) [[]] // expected-error {{standard attributes cannot appear after the namespace name}}
 {
 }
 
-namespace A [[]] __attribute__(())
+namespace A [[]] __attribute__(()) // expected-error {{standard attributes cannot appear after the namespace name}}
 {
 }
 
 namespace [[]] A __attribute__(())
 {
 }
 
-namespace __attribute__(()) A [[]]
+namespace __attribute__(()) A [[]] // expected-error {{standard attributes cannot appear after the namespace name}}
 {
 }
 
-namespace A::B __attribute__(()) // expected-error{{attributes cannot be specified on a nested namespace definition}}
+namespace A::B __attribute__(()) // expected-error {{attributes cannot be specified on a nested namespace definition}}
 {
 }
 
-namespace __attribute__(()) A::B // expected-error{{attributes cannot be specified on a nested namespace definition}}
+namespace __attribute__(()) A::B // expected-error {{attributes cannot be specified on a nested namespace definition}}
 {
 }