[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, 5 insertions, 1 deletions

diff --git a/clang/test/SemaObjC/attr-objc-gc.m b/clang/test/SemaObjC/attr-objc-gc.m
index 303dce0..e9dcbd9 100644
--- a/clang/test/SemaObjC/attr-objc-gc.m
+++ b/clang/test/SemaObjC/attr-objc-gc.m
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fsyntax-only -fdouble-square-bracket-attributes -verify %s
 static id __attribute((objc_gc(weak))) a;
 static id __attribute((objc_gc(strong))) b;
 
@@ -18,6 +18,10 @@ static WEAK int h; // expected-warning {{'objc_ownership' only applies to Object
 /* expected-warning {{'__weak' only applies to Objective-C object or block pointer types; type here is 'int'}}*/ static __we\
 ak int i;
 
+static id [[clang::objc_gc(weak)]] j;
+[[clang::objc_gc(weak)]] static id k; // expected-warning {{applying attribute 'objc_gc' to a declaration is deprecated; apply it to the type instead}}
+static id l [[clang::objc_gc(weak)]]; // expected-warning {{applying attribute 'objc_gc' to a declaration is deprecated; apply it to the type instead}}
+
 // rdar://problem/9126213
 void test2(id __attribute((objc_gc(strong))) *strong,
            id __attribute((objc_gc(weak))) *weak) {