Wireshark · Wireshark-dev: Re: [Wireshark-dev] cmake giving options the compiler does not understand

[Jeff Morriss <jeff.morriss.ws@xxxxxxxxx>]

On 01/03/2014 01:31 PM, Jeff Morriss wrote:
> On 01/02/2014 07:42 PM, Joerg Mayer wrote:
> > On Thu, Jan 02, 2014 at 04:30:14PM -0800, Guy Harris wrote:
> > > Are we really encountering a case where the C compiler accepts
> > > -Wshorten-64-to-32 but the C++ compiler doesn't, or *vice versa*?  Or
> > > are we encountering a case where *neither* compiler accepts it, but
> > > CMake isn't detecting that?
>
> Neither compiler supports that option.
>
> It's highly unlikely that this directory was previously used with a
> compiler that *did* support it (unless Fedora pushed out a compiler
> downgrade) but I suppose it is possible.
>
> > I don't know. On my (32-bit) system, both compilers correctly report that
> > it is not supported. I'd need to see the cmake output on a system that
> > has
> > this problem.
>
> Unfortunately the evidence is all gone now.  Maybe if I hit the problem
> again in the future...

Ah, OK, I found a way to reproduce it (in current SVN):

1) rm -rf _cmake_build
2) mkdir _cmake_build && cd _cmake_build
3) vi ../CMakeLists.txt
4) Move the "-Wshorten-64-to-32" flag from where it is in the file to 
just after "-Wshadow"
5) cmake ..
6) make # just to show that it works (I stopped the build after a few C 
files were compiled)
7) vi ../CMakeLists.txt
8) Put "-Wshorten-64-to-32" back where it was (at the end of 
WIRESHARK_C_ONLY_FLAGS)
9) cmake ..
10) make # now it doesn't work, complaining that "-Wshorten-64-to-32" is 
an unknown option

--> It seems cmake isn't caching the result of the test but rather the 
value of the variable we're storing the result in (e.g., WS_C_FLAG_VALID39).