[Development] Two source incompatibilities in Qt 5.5 with Clang

[Stephen Kelly]

Hello,

After commit ebef2ad1 (Make the empty Q_ASSERT still check its
argument for validity, 2014-09-11), there are two source
incompatibilities compared to Qt 5.4. I understand the message in the
commit.

The following code fails to compile with -DQT_NO_DEBUG:

sic.cpp:10:14: error: use of undeclared identifier 'checkInvariant'

    Q_ASSERT(checkInvariant());

             ^

qglobal.h:663:52: note: expanded from macro 'Q_ASSERT'

#    define Q_ASSERT(cond) do { } while (false && (cond))

                                                   ^

1 error generated.

$ cat sic.cpp

#include <QtCore/QObject>

#ifndef QT_NO_DEBUG

static bool checkInvariant() { return true; }

#endif

void foo()

{

    Q_ASSERT(checkInvariant());

}


If compiled with ccache, there is a second problem if used with
-Werror=unreachable-code:

sic.cpp:10:29: error: code will never be executed [-Werror,-Wunreachable-code]

    do { } while (false && (checkInvariant()));

                            ^~~~~~~~~~~~~~

sic.cpp:10:19: note: silence by adding parentheses to mark code as
explicitly dead

    do { } while (false && (checkInvariant()));

                  ^

                  /* DISABLES CODE */ ( )

1 error generated.


In this case, adding


 run_second_cpp = true


to


 ~/.ccache/ccache.conf


makes it compile without changing the macro.

If we want this source compatibility, both of these issues should be
mentioned in the release notes.

Thanks,

Steve.