[Development] Two source incompatibilities in Qt 5.5 with Clang

[Thiago Macieira]

On Thursday 05 March 2015 13:59:01 Stephen Kelly wrote:
> 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());
>              ^

This is not specific to Clang, it should happen with every compiler.

This was intentional and the minor SIC was expected. It only happens if you're 
calling a static function that only exists for Q_ASSERT -- not many people do 
that.

> 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 */ ( )

Interesting, will implement this.

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

I'll add the note to the Q_ASSERT and will add the parentheses.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center