MacOS: -Dcocoa=ON -Dopengl=OFF pass cmake but fail compilation

[pcanal]

On MacOS passing to cmake:

`-Dcocoa=ON -Dopengl=OFF`

leads to

/Users/pcanal/root_working/code/rootcling/graf2d/cocoa/src/TGCocoa.mm:20:10: fatal error: 'TGLIncludes.h' file not found
#include "TGLIncludes.h"
         ^~~~~~~~~~~~~~~
1 error generated.

In graf2d/cocoa/CMakeLists.txt the code:

if(opengl) # special case when cocoa is enabled but not opengl (i.e. gminimal=ON)
  target_include_directories(GCocoa PRIVATE ${OPENGL_INCLUDE_DIR})
else()
  target_include_directories(GCocoa PRIVATE
    ${CMAKE_SOURCE_DIR}/graf3d/gl/inc
  )
endif(opengl)

acknowledge the challenge but fail to address it.

And indeed in TGCocoa.mm the file TGLIncludes.h is always included.

Maybe this should fail at configuration time.

[couet]

I asked Timur about that. He told me that Cocca can be installed without OpenGl and a few ifdefs should make it. Indeed I just tried and found that in TGCocoa.mm, TGLIncludes.h should be under a "opengl ifdef"... in that same file glFlush(); should be also. Then in CMakeFiles/GCocoa.dir/link.txt , -lRGlew should not be generated.
So that mainly defining a new GL flag (or using an existing one) and changing the cmake procedure to avoid generating -lRGlew. May be @oshadura can help ?

[bellenot]

@pcanal before I look deeply into that, can you explain the specific use case for such combination? Is it really worth the effort?

[pcanal]

If i remember correctly I encountered this when starting from a minimal build (-Dminimal=ON) and then adding just -Dcocoa=ON and it fails.

I see 2 possible resolutions
(a) Implement what is hinted at in #7160 (comment)
(b) Have CMake fail for -Dcocoa=ON -Dopengl=OFF

[dpiparo]

I would go for (b) it looks simpler .