[CMake] Where do all the extra clang flags come from in Xcode?

[Ruslan Baratov]

On 14-May-15 23:53, Paul Smith wrote:
> I was comparing the command line used when we choose an Xcode generator
> on our OSX systems, vs. the command line used when we choose a Makefile
> generator.  We certainly have nothing in our CMakeLists.txt which sets
> compiler flags based on the type of generator, only based on the type of
> compiler (GCC, Clang, etc.)
>
> But, when I look at the compiler and flags used by the Makefile
> generator it uses /usr/bin/c++ (which is clang++ underneath) and it's
> basically only the the compiler flags that we provided.
>
> When I look at the compiler and flags used by the Xcode generator, not
> only does it use a different path to the compiler
> (/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -x c++) but, more concerning (because I assume that /usr/bin/clang++ eventually gets down to the same actual compiler as above) but it contains a huge number of extra flags, for example it appears to disable all sorts of warnings (that we don't want disabled):  -Wno-missing-prototypes, -Wno-return-type, -Wno-non-virtual-dtor, -Wno-overloaded-virtual, etc. etc.
>
> This means people who build on OSX using Makefile generators see extra
> warnings that people who build on OSX using Xcode don't see.
>
> Where are these extra flags all coming from?  Is it from Xcode itself
> somehow?  Can I keep them from being added?  I don't want peoples'
> personal Xcode settings to disable warnings during compilation!
>
> Note these are build servers and so no one is actually invoking Xcode:
> we log in via SSH, use cmake to generate the Xcode project files, then
> use cmake -build (which runs xcodebuild) to run the build itself.
>
As far as I know extra flags set by Xcode itself. You can use 
XCODE_ATTRIBUTE_* target properties to enable/disable warnings. This 
table can be helpful: 
https://github.com/ruslo/leathers/wiki/List#xcodeclang-table

Cheers, Ruslo