[LLVMbugs] [Bug 17234] New: Provide a way to check for RAII temporaries

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17234

            Bug ID: 17234
           Summary: Provide a way to check for RAII temporaries
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: benny.kra at gmail.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Take this example of a scoped RAII lock

void mutex_lock(int);
void mutex_unlock();

struct ScopedLock {
  __attribute__((warn_unused_result)) ScopedLock(int i) { mutex_lock(i); }
  ~ScopedLock() { mutex_unlock(); }
};

int main() {
  {
    ScopedLock(42);
    // Does not do what you might think.
    // more code ...
  }
}

The lock is immediately destroyed and does nothing, which is a typo. I tried to
add a warning here with the warn_unused_result attribute but clang only returns
a poorly worded warning:

warning: attribute 'warn_unused_result' cannot be applied to functions without
return value

It would be nice to have a way to warn on constructs like this.

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