[PATCH] D91913: Suppress non-conforming GNU paste extension in all standard-conforming modes

[Harald van Dijk via Phabricator via cfe-commits]

hvdijk created this revision.
hvdijk added a reviewer: rsmith.
hvdijk added a project: clang.
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hvdijk requested review of this revision.

The GNU token paste extension that removes the comma in , ## __VA_ARGS__ conflicts with C99/C++11's requirements when a variadic macro has no named parameters: according to the standard, an invocation as FOO() gives it a single empty argument, and concatenation of anything with an empty argument is well-defined. For this reason, the GNU extension was already disabled in C99 standard-conforming mode. It was not yet disabled in C++11 standard-conforming mode.

The associated comment suggested that GCC keeps this extension enabled in C90/C++03 standard-conforming mode, but it actually does not, so rather than adding a check for C++ language version, this change simply removes the check for C language version.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D91913

Files:
  clang/lib/Lex/TokenLexer.cpp
  clang/test/Preprocessor/macro_fn_comma_swallow2.c


Index: clang/test/Preprocessor/macro_fn_comma_swallow2.c
===================================================================
--- clang/test/Preprocessor/macro_fn_comma_swallow2.c
+++ clang/test/Preprocessor/macro_fn_comma_swallow2.c
@@ -1,9 +1,12 @@
 // Test the __VA_ARGS__ comma swallowing extensions of various compiler dialects.
 
 // RUN: %clang_cc1 -E %s | FileCheck -check-prefix=GCC -strict-whitespace %s
+// RUN: %clang_cc1 -E -std=c90 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
 // RUN: %clang_cc1 -E -std=c99 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
 // RUN: %clang_cc1 -E -std=c11 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
 // RUN: %clang_cc1 -E -x c++ %s | FileCheck -check-prefix=GCC -strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -std=c++03 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
+// RUN: %clang_cc1 -E -x c++ -std=c++11 %s | FileCheck -check-prefix=C99 -strict-whitespace %s
 // RUN: %clang_cc1 -E -std=gnu99 %s | FileCheck -check-prefix=GCC -strict-whitespace %s
 // RUN: %clang_cc1 -E -fms-compatibility %s | FileCheck -check-prefix=MS -strict-whitespace %s
 // RUN: %clang_cc1 -E -DNAMED %s | FileCheck -check-prefix=GCC -strict-whitespace %s
Index: clang/lib/Lex/TokenLexer.cpp
===================================================================
--- clang/lib/Lex/TokenLexer.cpp
+++ clang/lib/Lex/TokenLexer.cpp
@@ -148,12 +148,11 @@
     return false;
 
   // GCC removes the comma in the expansion of " ... , ## __VA_ARGS__ " if
-  // __VA_ARGS__ is empty, but not in strict C99 mode where there are no
-  // named arguments, where it remains.  In all other modes, including C99
-  // with GNU extensions, it is removed regardless of named arguments.
+  // __VA_ARGS__ is empty, but not in strict mode where there are no
+  // named arguments, where it remains.  With GNU extensions, it is removed
+  // regardless of named arguments.
   // Microsoft also appears to support this extension, unofficially.
-  if (PP.getLangOpts().C99 && !PP.getLangOpts().GNUMode
-        && Macro->getNumParams() < 2)
+  if (!PP.getLangOpts().GNUMode && Macro->getNumParams() < 2)
     return false;
 
   // Is a comma available to be removed?


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