[Interest] [OS X] How to enable ARC for *.mm files (which qmake var)?

[Thiago Macieira]

On sexta-feira, 17 de janeiro de 2014 21:20:29, Till Oliver Knoll wrote:
> Am 17.01.14 00:55, schrieb Thiago Macieira:
> > On sexta-feira, 17 de janeiro de 2014 00:07:07, Till Oliver Knoll
> > 
> > wrote:
> >> QMAKE_CXXFLAGS += -fobjc-arc QMAKE_CFLAGS_DEBUG += -fobjc-arc
> >> QMAKE_CFLAGS_RELEASE += -fobjc-arc
> >> 
> >> 
> >> That is, the expected -fobjc-arc flag is only applied for
> >> clang++.
> > 
> > "CXXFLAGS" applies to C++ and Objective C++.
> 
> Are you /sure/ you mean CXXFLAGS and not QMAKE_CXXFLAGS? In fact, I
> just tried setting CXXFLAGS and it does not seem to have any effect:
> 
>   CXXFLAGS += -fobjc-arc

It was QMAKE_CXXFLAGS. What I meant is that, in general, "CXXFLAGS" in 
Makefiles and other buildsystem related tools related to C++. CFLAGS applies to 
C. And CPPFLAGS is about the C preprocessor.

> -> the compiler flag is /not/ added, neither when compiling my ObjC++
> *.mm files (as expected), nor to my C++ *.cpp files.
> 
>   QMAKE_CXXFLAGS += -fobjc-arc
> 
> on the other hand /does/ add that option when compiling my C++ files,
> but naturally enabling Automatic Reference Counting (ARC - a feature
> which makes only sense when compiling Objective C/C++) has no effect
> in the C++ world.

Good. I feared it would generate a compiler error "no such option for this 
file".

> According to
> 
>   http://qt-project.org/doc/qt-5/qmake-variable-reference.html
> 
> the variable QMAKE_CFLAGS does not exist (at least it is not
> documented). So I assume that it would work for C files in analogy to
> how QMAKE_CXXFLAGS works for compiling C++ files (which /is/ documented).

It does exist and is used throughout the qmake source code and .prf files. It 
appears not to be documented, though, like most of qmake.

> > Note that this will get the flags for plain C and C++ sources too.
> 
> No, setting
> 
>   QMAKE_CFLAGS += -fobjc-arc
> 
> has no effect, neither on the *.mm nor on the *.cpp files. At least
> that flag was not set when clang++ was invoced. And to be honest, I
> would not expect flags set for a C compiler to take effect when
> compiling C++ sources either.

It shouldn't. That variable should only affect *.c and *.m (which get "clang", 
not "clang++" run).

> > I don't see an equivalent flag for ObjC++.
> 
> I don't see e.g. QMAKE_OBJECTIVE_CXXFLAGS either (and it does not work).
> 
> But when you mention "see" you probably refer to various Qt project
> *.pro files, GIT commit messages of "Chromium" etc., as in

When I mean "see", I mean doing this search in qtbase:

	git grep OBJECTIVE_CXXFLAGS -- mkspecs qmake

If you want to do any advanced thing with qmake, you need to read those two 
dirs and see what they do. There's a lot of undocumented code.

Which can break in the next version, because it's undocumented.
-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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