MantisBT - CMake
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IDProjectCategoryView StatusDate SubmittedLast Update
0004756CMakeCMakepublic2007-04-02 16:542016-06-10 14:30
ReporterSean McBride 
Assigned ToKitware Robot 
PrioritynormalSeverityfeatureReproducibilityalways
StatusclosedResolutionmoved 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version 
Summary0004756: CMake needs an Objective-C equivalent of CMAKE_CXX_FLAGS
DescriptionCMake provides CMAKE_CXX_FLAGS and CMAKE_C_FLAGS to supply compiler flags that are only supported by C++ and C respectively.

It is however lacking an analogous feature for Objective-C. That is, we need a CMAKE_OBJC_FLAGS.

In many cases, gcc on Mac OS X actually gives a warning when a flag is passed when compiling for a language that does not support the flag. For example, the '-fobjc-gc' flag if passed when building C++ warns:

"cc1plus: warning: command line option "-fobjc-gc" is valid for ObjC/ObjC++ but not for C++"

Objective-C files can be recognised by the .m filename extension.

There is also Objective-C++, recognised by the .mm extension, that allows both C++ and Obj-C syntax in the same file. In this case, we could either have a CMAKE_OBJCXX_FLAGS or apply both CMAKE_CXX_FLAGS and CMAKE_OBJC_FLAGS to those files. I believe I prefer the latter, but I have not given it too much thought.
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Issue History
Date ModifiedUsernameFieldChange
2007-11-21 11:11Sean McBrideNote Added: 0009718
2007-12-18 10:34Sean McBrideNote Added: 0009978
2010-07-05 15:34Sean McBrideNote Added: 0021244
2011-12-20 08:41Brad KingNote Added: 0028019
2011-12-20 12:17Eric WingNote Added: 0028022
2011-12-20 15:38Sean McBrideNote Added: 0028023
2012-01-03 13:43David ColeNote Added: 0028146
2012-01-03 14:23Brad KingNote Added: 0028147
2014-02-14 14:09Brad KingAssigned ToBill Hoffman => Steve Wilson
2014-02-14 14:09Brad KingTarget Version => CMake 3.1
2014-10-03 09:33Brad KingAssigned ToSteve Wilson =>
2014-10-03 09:33Brad KingStatusassigned => backlog
2014-10-03 09:33Brad KingTarget VersionCMake 3.1 =>
2016-06-10 14:27Kitware RobotNote Added: 0041351
2016-06-10 14:27Kitware RobotStatusbacklog => resolved
2016-06-10 14:27Kitware RobotResolutionopen => moved
2016-06-10 14:27Kitware RobotAssigned To => Kitware Robot
2016-06-10 14:30Kitware RobotStatusresolved => closed

Notes
(0007072)
Eric Wing   
2007-04-02 17:09   
Actually, I think you would need both/separate CMAKE_OBJC_FLAGS and CMAKE_OBJCXX_FLAGS. The problem is that there are some Obj-C++ only flags such as -fobjc-call-cxx-cdtors (Run non-trivial default constructors and destructors on C++ instance variables of Objective-C classes). This one is critical if you have C++ ivars (not pointers to) contained in an Obj-C class. But it is meaningless to pure C/Obj-C and pure C++ code.
(0007909)
Sean McBride   
2007-06-19 13:48   
Eric, you are quite right, CMake does need both.
(0009718)
Sean McBride   
2007-11-21 11:11   
In VTK, if one enables Garbage Collection in Cocoa, one gets many warnings:

http://www.vtk.org/Testing/Sites/RogueResearch4/Mac10.5-VTKBS-dbg/20071121-0300-Nightly/BuildWarning.html [^]
(0009978)
Sean McBride   
2007-12-18 10:34   
Committed a workaround for the VTK case, to eliminate all the warnings when doing a GC build of VTK Cocoa:

/cvsroot/VTK/VTK/Rendering/CMakeLists.txt,v <-- CMakeLists.txt
new revision: 1.267; previous revision: 1.266
(0021244)
Sean McBride   
2010-07-05 15:34   
Just to ping this bug.... Nothing much has changed as of 2.8.2. I'd still like to see this supported.
(0028019)
Brad King   
2011-12-20 08:41   
Should all C flags be used for ObjC too, and C++ flags for ObjC++?

I think the real change needed here may be to split ObjC and ObjCXX out into their own languages that need to be enabled by the project() or enable_language() commands. Then they will be fully distinct and can have their own compiler flags and such. Achieving this with compatibility though will require a policy:

  http://www.cmake.org/Wiki/CMake/Policies [^]
(0028022)
Eric Wing   
2011-12-20 12:17   
Obj-C is a pure 100% superset of C. It seems reasonable that C flags be used for ObjC.
I think it is safe to extend that idea for C++ to ObjC++.

I am having trouble imagining a real world case where you would not want the flags passed on.
(0028023)
Sean McBride   
2011-12-20 15:38   
I concur with Eric here...
(0028146)
David Cole   
2012-01-03 13:43   
This seems like a large amount of work for a very small benefit. Is there anybody listening in on this issue who can supply a patch, including, but not limited to the following:

- adding new languages ObjC and ObjCXX
- adding new flags for the languages
- associating *.m and *.mm files with the languages
- creating a policy
- adding a test
- following up on the dashboard when things go wrong on various Mac submissions

Anybody have time to work on a patch?
(0028147)
Brad King   
2012-01-03 14:23   
Re 0004756:0028146: I think the discussion here has concluded that we do not need new languages ObjC and ObjCXX but can instead just add the extra flags for *.m and *.mm sources with a special case. The simplest generalization of the special case I can think of is to define "variants" of a language that get special flags.
(0041351)
Kitware Robot   
2016-06-10 14:27   
Resolving issue as `moved`.

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