[NFC] Use RAII to un-poison and then re-poison __VA_ARGS__

  - This will also be used for the forthcoming __VA_OPT__ feature approved for C++2a.
  - recommended by rsmith during his review of the __VA_OPT__ patch (https://reviews.llvm.org/D35782)

llvm-svn: 308948

1 files changed, 12 insertions, 13 deletions

diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index b2450f516ba..6b09398e468 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -33,6 +33,7 @@
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Lex/PTHLexer.h"
 #include "clang/Lex/Token.h"
+#include "clang/Lex/VariadicMacroSupport.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
@@ -2290,6 +2291,10 @@ MacroInfo *Preprocessor::ReadOptionalMacroParameterListAndBody(
   Token Tok;
   LexUnexpandedToken(Tok);
 
+  // Used to un-poison and then re-poison identifiers of the __VA_ARGS__ ilk
+  // within their appropriate context.
+  VariadicMacroScopeGuard VariadicMacroScopeGuard(*this);
+
   // If this is a function-like macro definition, parse the argument list,
   // marking each of the identifiers as being used as macro arguments.  Also,
   // check other constraints on the first token of the macro body.
@@ -2314,14 +2319,14 @@ MacroInfo *Preprocessor::ReadOptionalMacroParameterListAndBody(
       return nullptr;
     }
 
-    // If this is a definition of a variadic C99 function-like macro, not using
-    // the GNU named varargs extension, enabled __VA_ARGS__.
+    // If this is a definition of an ISO C/C++ variadic function-like macro (not
+    // using the GNU named varargs extension) inform our variadic scope guard
+    // which un-poisons and re-poisons certain identifiers (e.g. __VA_ARGS__)
+    // allowed only within the definition of a variadic macro.
 
-    // "Poison" __VA_ARGS__, which can only appear in the expansion of a macro.
-    // This gets unpoisoned where it is allowed.
-    assert(Ident__VA_ARGS__->isPoisoned() && "__VA_ARGS__ should be poisoned!");
-    if (MI->isC99Varargs())
-      Ident__VA_ARGS__->setIsPoisoned(false);
+    if (MI->isC99Varargs()) {
+      VariadicMacroScopeGuard.enterScope();
+    }
 
     // Read the first token after the arg list for down below.
     LexUnexpandedToken(Tok);
@@ -2431,9 +2436,6 @@ MacroInfo *Preprocessor::ReadOptionalMacroParameterListAndBody(
         } else {
           Diag(Tok, diag::err_pp_stringize_not_parameter)
             << LastTok.is(tok::hashat);
-
-          // Disable __VA_ARGS__ again.
-          Ident__VA_ARGS__->setIsPoisoned(true);
           return nullptr;
         }
       }
@@ -2448,9 +2450,6 @@ MacroInfo *Preprocessor::ReadOptionalMacroParameterListAndBody(
     }
   }
   MI->setDefinitionEndLoc(LastTok.getLocation());
-  // Disable __VA_ARGS__ again.
-  Ident__VA_ARGS__->setIsPoisoned(true);
-
   return MI;
 }
 /// HandleDefineDirective - Implements \#define.  This consumes the entire macro