Unverified Commit f4537935 authored by Harald van Dijk's avatar Harald van Dijk
Browse files

Suppress non-conforming GNU paste extension in all standard-conforming modes 

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.

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D91913
parent a80ebd01

clang/lib/Lex/TokenLexer.cpp

+4 −5
Original line number Diff line number Diff line
@@ -148,12 +148,11 @@ bool TokenLexer::MaybeRemoveCommaBeforeVaArgs( 
    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?

clang/test/Preprocessor/macro_fn_comma_swallow2.c

+3 −0
Original line number Diff line number Diff line 
// 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