[LLVMbugs] [Bug 12767] New: The preprocessor doesn't inhibit expansion when concatenating with an empty token

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12767

             Bug #: 12767
           Summary: The preprocessor doesn't inhibit expansion when
                    concatenating with an empty token
           Product: clang
           Version: 3.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: pfultz2 at yahoo.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


The preprocessor doesn't inhibit expansion when concatenating with an empty
token.
Here an example:

#define EMPTY()
#define DEFER(id) id EMPTY()

#define A(p, ...) p ## __VA_ARGS__ // should inhibit expansion of ...

#define B(p, ...) p __VA_ARGS__

#define TEST() 123

A(, DEFER(TEST)()) // should be TEST (), but clang expands to 123
B(, DEFER(TEST)()) // should be 123

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