Infrastructure for adding C attributes

[aaron.ballman]

Summary

This patch extends the Clang attribute spelling to include support for double square-bracket attributes. Currently, all attributes with the Clang spelling will be C++ only. However, at some point I suspect the default will either switch to be a spelling for C and C++ or will require an explicit decision to be made for each attribute.

This patch adds the annotate attribute as a C attribute as an initial experiment. Additional attributes will be added in follow-up patches.

[aaron.ballman]

Ping

[aaron.ballman]

Post-holiday ping.

[aaron.ballman]

I commit in r321763. I changed the name of IncludeC to be AllowInC at John McCall's suggestion.

include/clang/Basic/Attr.td

   let KnownToGCC = 1;
 }
 
-// The Clang spelling implies GNU<name> and CXX11<"clang", name>. This spelling
-// should be used for any Clang-specific attributes.
-class Clang<string name> : Spelling<name, "Clang">;
+// The Clang spelling implies GNU<name>, CXX11<"clang", name>, and optionally,
+// C2x<"clang", name>. This spelling should be used for any Clang-specific
+// attributes.
+class Clang<string name, bit includeC = 0> : Spelling<name, "Clang"> {
+  bit IncludeC = includeC;
+}
 
 class Accessor<string name, list<Spelling> spellings> {
   string Name = name;

 }
 
 def Annotate : InheritableParamAttr {
-  let Spellings = [Clang<"annotate">];
+  let Spellings = [Clang<"annotate", 1>];
   let Args = [StringArgument<"Annotation">];
   // Ensure that the annotate attribute can be used with
   // '#pragma clang attribute' even though it has no subject list.

test/Sema/annotate.c

-// RUN: %clang_cc1 %s -fsyntax-only -verify
+// RUN: %clang_cc1 %s -fsyntax-only -fdouble-square-bracket-attributes -verify
 
 void __attribute__((annotate("foo"))) foo(float *a) {
   __attribute__((annotate("bar"))) int x;
+  [[clang::annotate("bar")]] int x2;
   __attribute__((annotate(1))) int y; // expected-error {{'annotate' attribute requires a string}}
+  [[clang::annotate(1)]] int y2; // expected-error {{'annotate' attribute requires a string}}
   __attribute__((annotate("bar", 1))) int z; // expected-error {{'annotate' attribute takes one argument}}
+  [[clang::annotate("bar", 1)]] int z2; // expected-error {{'annotate' attribute takes one argument}}
+
   int u = __builtin_annotation(z, (char*) 0); // expected-error {{second argument to __builtin_annotation must be a non-wide string constant}}
   int v = __builtin_annotation(z, (char*) L"bar"); // expected-error {{second argument to __builtin_annotation must be a non-wide string constant}}
   int w = __builtin_annotation(z, "foo");

utils/TableGen/ClangAttrEmitter.cpp

     } else if (Variety == "Clang") {
       Ret.emplace_back("GNU", Name, "", false);
       Ret.emplace_back("CXX11", Name, "clang", false);
+      if (Spelling->getValueAsBit("IncludeC"))
+        Ret.emplace_back("C2x", Name, "clang", false);
     } else
       Ret.push_back(FlattenedSpelling(*Spelling));
   }