[LLVMbugs] [Bug 12845] New: Incorrect expansion of a macro defining a function with variable arguments

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12845

             Bug #: 12845
           Summary: Incorrect expansion of a macro defining a function
                    with variable arguments
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: eremeev at viva64.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


When passing a single argument to a macro which defines a function with a
variable arguments list as its' second argument, Clang will incorrectly
preprocess such code, leaving the unnecessary comma after the first argument,
thus making the resulting code uncompilable. Consider the example:

bool MsgAlert(bool yes_no, int Style, const char* format, ...)
{return true;}
#define PanicAlert(format, ...) MsgAlert(false, 1, format, __VA_ARGS__) 

void func()
{PanicAlert("text");}

Clang preprocessor (the -E flag, in MS compatibility mode) will generate the
following (note the excessive comma after "text"):

void func()
{MsgAlert(false, 1, "text", );}

In comparison,  the MSVC preprocessor (cl.exe) will generate the correct code:

void func()
{MsgAlert(false, 1, "text"  );}

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