Emit an extension warning when changing system header tokens

clang converts keywords to identifiers for compatibility with various system
headers such as GNU libc.

Implement a -Wkeyword-compat extension warning to diagnose those cases. The
warning is on by default but will generally be ignored in system headers. It
can however be enabled globally to aid standards conformance testing.

This also changes the __uptr keyword avoidance from r195710 to no longer
special-case system headers, bringing it in line with other similar workarounds
in clang.

Implementation returns bool for symmetry with token annotation functions.

Some examples:

warning: keyword '__is_pod' will be treated as an identifier for the remainder of the translation unit [-Wkeyword-compat]
struct __is_pod

warning: keyword '__uptr' will be treated as an identifier here [-Wkeyword-compat]
union w *__uptr;

llvm-svn: 196212

clang/include/clang/Basic/DiagnosticGroups.td

@@ -50,6 +50,7 @@ def BuiltinRequiresHeader : DiagGroup<"builtin-requires-header">;
 def C99Compat : DiagGroup<"c99-compat">;
 def CXXCompat: DiagGroup<"c++-compat">;
 def ExternCCompat : DiagGroup<"extern-c-compat">;
+def KeywordCompat : DiagGroup<"keyword-compat">;
 def GNUCaseRange : DiagGroup<"gnu-case-range">;
 def CastAlign : DiagGroup<"cast-align">;
 def : DiagGroup<"cast-qual">;

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -58,6 +58,9 @@ def ext_plain_complex : ExtWarn<
 def ext_integer_complex : Extension<
   "complex integer types are a GNU extension">, InGroup<GNUComplexInteger>;
 def ext_thread_before : Extension<"'__thread' before '%0'">;
+def ext_keyword_as_ident : ExtWarn<
+  "keyword '%0' will be treated as an identifier %select{here|for the remainder of the translation unit}1">,
+  InGroup<KeywordCompat>;
 
 def error_empty_enum : Error<"use of empty enum">;
 def err_invalid_sign_spec : Error<"'%0' cannot be signed or unsigned">;

clang/include/clang/Parse/Parser.h

@@ -563,6 +563,13 @@ private:
                                 const char *&PrevSpec, unsigned &DiagID,
                                 bool &isInvalid);
 
+  /// TryKeywordIdentFallback - For compatibility with system headers using
+  /// keywords as identifiers, attempt to convert the current token to an
+  /// identifier and optionally disable the keyword for the remainder of the
+  /// translation unit. This returns false if the token was not replaced,
+  /// otherwise emits a diagnostic and returns true.
+  bool TryKeywordIdentFallback(bool DisableKeyword);
+
   /// \brief Get the TemplateIdAnnotation from the token.
   TemplateIdAnnotation *takeTemplateIdAnnotation(const Token &tok);
 

clang/lib/Parse/ParseDecl.cpp

@@ -2739,10 +2739,8 @@ void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
       // then treat __is_signed as an identifier rather than as a keyword.
       if (DS.getTypeSpecType() == TST_bool &&
           DS.getTypeQualifiers() == DeclSpec::TQ_const &&
-          DS.getStorageClassSpec() == DeclSpec::SCS_static) {
-        Tok.getIdentifierInfo()->RevertTokenIDToIdentifier();
-        Tok.setKind(tok::identifier);
-      }
+          DS.getStorageClassSpec() == DeclSpec::SCS_static)
+        TryKeywordIdentFallback(true);
 
       // We're done with the declaration-specifiers.
       goto DoneWithDeclSpec;
@@ -4488,10 +4486,9 @@ void Parser::ParseTypeQualifierListOpt(DeclSpec &DS,
       // GNU libc headers in C mode use '__uptr' as an identifer which conflicts
       // with the MS modifier keyword.
       if (VendorAttributesAllowed && !getLangOpts().CPlusPlus &&
-          IdentifierRequired && DS.isEmpty() && NextToken().is(tok::semi) &&
-          PP.getSourceManager().isInSystemHeader(Loc)) {
-        Tok.setKind(tok::identifier);
-        continue;
+          IdentifierRequired && DS.isEmpty() && NextToken().is(tok::semi)) {
+        if (TryKeywordIdentFallback(false))
+          continue;
       }
     case tok::kw___sptr:
     case tok::kw___w64:

clang/lib/Parse/ParseDeclCXX.cpp

@@ -1198,15 +1198,13 @@ void Parser::ParseClassSpecifier(tok::TokenKind TagTokKind,
        Tok.is(tok::kw___is_scalar) ||
        Tok.is(tok::kw___is_signed) ||
        Tok.is(tok::kw___is_unsigned) ||
-       Tok.is(tok::kw___is_void))) {
+       Tok.is(tok::kw___is_void)))
     // GNU libstdc++ 4.2 and libc++ use certain intrinsic names as the
     // name of struct templates, but some are keywords in GCC >= 4.3
     // and Clang. Therefore, when we see the token sequence "struct
     // X", make X into a normal identifier rather than a keyword, to
     // allow libstdc++ 4.2 and libc++ to work properly.
-    Tok.getIdentifierInfo()->RevertTokenIDToIdentifier();
-    Tok.setKind(tok::identifier);
-  }
+    TryKeywordIdentFallback(true);
 
   // Parse the (optional) nested-name-specifier.
   CXXScopeSpec &SS = DS.getTypeSpecScope();

clang/lib/Parse/Parser.cpp

@@ -1517,6 +1517,17 @@ Parser::TryAnnotateName(bool IsAddressOfOperand,
   return ANK_Unresolved;
 }
 
+bool Parser::TryKeywordIdentFallback(bool DisableKeyword) {
+  assert(Tok.isNot(tok::identifier));
+  Diag(Tok, diag::ext_keyword_as_ident)
+    << PP.getSpelling(Tok)
+    << DisableKeyword;
+  if (DisableKeyword)
+    Tok.getIdentifierInfo()->RevertTokenIDToIdentifier();
+  Tok.setKind(tok::identifier);
+  return true;
+}
+
 /// TryAnnotateTypeOrScopeToken - If the current token position is on a
 /// typename (possibly qualified in C++) or a C++ scope specifier not followed
 /// by a typename, TryAnnotateTypeOrScopeToken will replace one or more tokens

clang/test/PCH/cxx-traits.cpp

@@ -2,9 +2,11 @@
 // RUN: %clang_cc1 -include %S/cxx-traits.h -std=c++11 -fsyntax-only -verify %s
 
 // RUN: %clang_cc1 -x c++-header -std=c++11 -emit-pch -o %t %S/cxx-traits.h
-// RUN: %clang_cc1 -std=c++11 -include-pch %t -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++11 -include-pch %t -DPCH -fsyntax-only -verify %s
 
+#ifdef PCH
 // expected-no-diagnostics
+#endif
 
 bool _Is_pod_comparator = __is_pod<int>::__value;
 bool _Is_empty_check = __is_empty<int>::__value;

clang/test/PCH/cxx-traits.h

@@ -1,12 +1,12 @@
 // Header for PCH test cxx-traits.cpp
 
 template<typename _Tp>
-struct __is_pod {
+struct __is_pod { // expected-warning {{keyword '__is_pod' will be treated as an identifier for the remainder of the translation unit}}
   enum { __value };
 };
 
 template<typename _Tp>
-struct __is_empty {
+struct __is_empty { // expected-warning {{keyword '__is_empty' will be treated as an identifier for the remainder of the translation unit}}
   enum { __value };
 };
 

clang/test/Sema/Inputs/ms-keyword-system-header.h

@@ -2,5 +2,8 @@
 
 typedef union {
   union w *__uptr;
+#if defined(MS) && defined(NOT_SYSTEM)
+  // expected-warning@-2 {{keyword '__uptr' will be treated as an identifier here}}
+#endif
   int *__iptr;
 } WS __attribute__((__transparent_union__));

clang/test/Sema/ms-keyword-system-header.c

@@ -1,4 +1,6 @@
 // RUN: %clang_cc1 -fms-extensions -D MS -isystem %S/Inputs %s -fsyntax-only -verify
+// RUN: %clang_cc1 -fms-extensions -D MS -Wno-keyword-compat -I %S/Inputs %s -fsyntax-only -verify
+// RUN: %clang_cc1 -fms-extensions -D MS -D NOT_SYSTEM -I %S/Inputs %s -fsyntax-only -verify
 // RUN: %clang_cc1 -isystem %S/Inputs %s -fsyntax-only -verify
 
 // PR17824: GNU libc uses MS keyword __uptr as an identifier in C mode