[clang] Reject non-declaration C++11 attributes on declarations

For backwards compatiblity, we emit only a warning instead of an error if the
attribute is one of the existing type attributes that we have historically
allowed to "slide" to the `DeclSpec` just as if it had been specified in GNU
syntax. (We will call these "legacy type attributes" below.)

The high-level changes that achieve this are:

- We introduce a new field `Declarator::DeclarationAttrs` (with appropriate
  accessors) to store C++11 attributes occurring in the attribute-specifier-seq
  at the beginning of a simple-declaration (and other similar declarations).
  Previously, these attributes were placed on the `DeclSpec`, which made it
  impossible to reconstruct later on whether the attributes had in fact been
  placed on the decl-specifier-seq or ahead of the declaration.

- In the parser, we propgate declaration attributes and decl-specifier-seq
  attributes separately until we can place them in
  `Declarator::DeclarationAttrs` or `DeclSpec::Attrs`, respectively.

- In `ProcessDeclAttributes()`, in addition to processing declarator attributes,
  we now also process the attributes from `Declarator::DeclarationAttrs` (except
  if they are legacy type attributes).

- In `ConvertDeclSpecToType()`, in addition to processing `DeclSpec` attributes,
  we also process any legacy type attributes that occur in
  `Declarator::DeclarationAttrs` (and emit a warning).

- We make `ProcessDeclAttribute` emit an error if it sees any non-declaration
  attributes in C++11 syntax, except in the following cases:
  - If it is being called for attributes on a `DeclSpec` or `DeclaratorChunk`
  - If the attribute is a legacy type attribute (in which case we only emit
    a warning)

The standard justifies treating attributes at the beginning of a
simple-declaration and attributes after a declarator-id the same. Here are some
relevant parts of the standard:

- The attribute-specifier-seq at the beginning of a simple-declaration
  "appertains to each of the entities declared by the declarators of the
  init-declarator-list" (https://eel.is/c++draft/dcl.dcl#dcl.pre-3)

- "In the declaration for an entity, attributes appertaining to that entity can
  appear at the start of the declaration and after the declarator-id for that
  declaration." (https://eel.is/c++draft/dcl.dcl#dcl.pre-note-2)

- "The optional attribute-specifier-seq following a declarator-id appertains to
  the entity that is declared."
  (https://eel.is/c++draft/dcl.dcl#dcl.meaning.general-1)

The standard contains similar wording to that for a simple-declaration in other
similar types of declarations, for example:

- "The optional attribute-specifier-seq in a parameter-declaration appertains to
  the parameter." (https://eel.is/c++draft/dcl.fct#3)

- "The optional attribute-specifier-seq in an exception-declaration appertains
  to the parameter of the catch clause" (https://eel.is/c++draft/except.pre#1)

The new behavior is tested both on the newly added type attribute
`annotate_type`, for which we emit errors, and for the legacy type attribute
`address_space` (chosen somewhat randomly from the various legacy type
attributes), for which we emit warnings.

Depends On D111548

Reviewed By: aaron.ballman, rsmith

Differential Revision: https://reviews.llvm.org/D126061

1 files changed, 20 insertions, 8 deletions

diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index 7ffaf05..7fad3b2 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -740,6 +740,9 @@ bool Parser::ParseTopLevelDecl(DeclGroupPtrTy &Result,
 
 /// ParseExternalDeclaration:
 ///
+/// The `Attrs` that are passed in are C++11 attributes and appertain to the
+/// declaration.
+///
 ///       external-declaration: [C99 6.9], declaration: [C++ dcl.dcl]
 ///         function-definition
 ///         declaration
@@ -929,7 +932,9 @@ Parser::DeclGroupPtrTy Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
     // A function definition cannot start with any of these keywords.
     {
       SourceLocation DeclEnd;
-      return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs);
+      ParsedAttributes EmptyDeclSpecAttrs(AttrFactory);
+      return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs,
+                              EmptyDeclSpecAttrs);
     }
 
   case tok::kw_static:
@@ -939,7 +944,9 @@ Parser::DeclGroupPtrTy Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
       Diag(ConsumeToken(), diag::warn_static_inline_explicit_inst_ignored)
         << 0;
       SourceLocation DeclEnd;
-      return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs);
+      ParsedAttributes EmptyDeclSpecAttrs(AttrFactory);
+      return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs,
+                              EmptyDeclSpecAttrs);
     }
     goto dont_know;
 
@@ -950,7 +957,9 @@ Parser::DeclGroupPtrTy Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
       // Inline namespaces. Allowed as an extension even in C++03.
       if (NextKind == tok::kw_namespace) {
         SourceLocation DeclEnd;
-        return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs);
+        ParsedAttributes EmptyDeclSpecAttrs(AttrFactory);
+        return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs,
+                                EmptyDeclSpecAttrs);
       }
 
       // Parse (then ignore) 'inline' prior to a template instantiation. This is
@@ -959,7 +968,9 @@ Parser::DeclGroupPtrTy Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
         Diag(ConsumeToken(), diag::warn_static_inline_explicit_inst_ignored)
           << 1;
         SourceLocation DeclEnd;
-        return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs);
+        ParsedAttributes EmptyDeclSpecAttrs(AttrFactory);
+        return ParseDeclaration(DeclaratorContext::File, DeclEnd, Attrs,
+                                EmptyDeclSpecAttrs);
       }
     }
     goto dont_know;
@@ -1112,8 +1123,6 @@ Parser::DeclGroupPtrTy Parser::ParseDeclOrFunctionDefInternal(
     return Actions.ConvertDeclToDeclGroup(TheDecl);
   }
 
-  DS.takeAttributesFrom(Attrs);
-
   // ObjC2 allows prefix attributes on class interfaces and protocols.
   // FIXME: This still needs better diagnostics. We should only accept
   // attributes here, no types, etc.
@@ -1128,6 +1137,7 @@ Parser::DeclGroupPtrTy Parser::ParseDeclOrFunctionDefInternal(
     }
 
     DS.abort();
+    DS.takeAttributesFrom(Attrs);
 
     const char *PrevSpec = nullptr;
     unsigned DiagID;
@@ -1151,11 +1161,12 @@ Parser::DeclGroupPtrTy Parser::ParseDeclOrFunctionDefInternal(
   if (getLangOpts().CPlusPlus && isTokenStringLiteral() &&
       DS.getStorageClassSpec() == DeclSpec::SCS_extern &&
       DS.getParsedSpecifiers() == DeclSpec::PQ_StorageClassSpecifier) {
+    ProhibitAttributes(Attrs);
     Decl *TheDecl = ParseLinkage(DS, DeclaratorContext::File);
     return Actions.ConvertDeclToDeclGroup(TheDecl);
   }
 
-  return ParseDeclGroup(DS, DeclaratorContext::File);
+  return ParseDeclGroup(DS, DeclaratorContext::File, Attrs);
 }
 
 Parser::DeclGroupPtrTy Parser::ParseDeclarationOrFunctionDefinition(
@@ -1473,7 +1484,8 @@ void Parser::ParseKNRParamDeclarations(Declarator &D) {
     }
 
     // Parse the first declarator attached to this declspec.
-    Declarator ParmDeclarator(DS, DeclaratorContext::KNRTypeList);
+    Declarator ParmDeclarator(DS, ParsedAttributesView::none(),
+                              DeclaratorContext::KNRTypeList);
     ParseDeclarator(ParmDeclarator);
 
     // Handle the full declarator list.