[llvm-bugs] [Bug 24404] New: Missing result unused after macro expansion

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=24404

            Bug ID: 24404
           Summary: Missing result unused after macro expansion
           Product: clang
           Version: unspecified
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: adkap at adkap.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

This follows from a bug in a popular Obj-C testing framework Expecta:
https://github.com/specta/expecta/issues/160

Basically, a macro evaluates to an Objective-C object pointer, is sent a
message, and the result is unused. There is no warning produced. However if the
macro is enclosed in parens/(), the warning is produced as expected.

This isn't an academic case: I had several tests "pass" because the trailing
parentheses were accidentally omitted.

A very short example

https://gist.github.com/adamkaplan/3c69fda47bf02790a860#file-expexpectawarningdemo-m

My configuration:
Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.4.0

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