Macro Redefinition in MSVC compatibility mode

[llvmbot]

Bugzilla Link	11583
Resolution	WONTFIX
Resolved on	Sep 21, 2015 21:58
Version	trunk
OS	Windows XP
Blocks	llvm/llvm-bugzilla-archive#13707
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor,@tritao,@nico

Extended Description

In code containing function-like macro overloading, for example:

#define RETERROR(x) return x
#define RETERROR(x,y) return x + 1

int test()
{
RETERROR(2);
}

Visual C++ compiler is able to processes this code, generating the C4003 warning (the missing argument being replaced by an empty string), while clang exits with an error "too few arguments provided to function-like macro invocation", being unable to process it and potentially making some Visual C++ projects uncompilable.

[DougGregor]

It's not clear to me that we'll ever want to support this in Clang, because absolute compatibility with MSVC is not a goal for the project. If this shows up in platform headers somewhere, then it might be worth doing.

[nico]

Looks like this isn't needed to parse any system headers.

[tritao]

mentioned in issue llvm/llvm-bugzilla-archive#13707