[CMake] Problem with try_compile() for iOS

[Eric Doenges]

Hi,

I'm currently testing CMake 3.14.2's iOS support with our build system 
and ran into a problem with try_compile() not finding the binary. Here 
is an example while trying to configure libjpeg-turbo 2.0.2 (I've 
shortened the paths to make this easier to read):

--- SNIP ---

-- Check size of size_t
CMake Error at share/cmake-3.14/Modules/CheckTypeSize.cmake:120 
(try_compile):
   Cannot copy output executable

     ''

   to destination specified by COPY_FILE:

'libjpegturbo_library-ext-build/CMakeFiles/CheckTypeSize/SIZE_T.bin'

   Unable to find the executable at any of:

     libjpegturbo_library-ext-build/CMakeFiles/CMakeTmp/cmTC_3f58e
libjpegturbo_library-ext-build/CMakeFiles/CMakeTmp/Debug/cmTC_3f58e
libjpegturbo_library-ext-build/CMakeFiles/CMakeTmp/Debug/cmTC_3f58e.app/cmTC_3f58e
libjpegturbo_library-ext-build/CMakeFiles/CMakeTmp/Development/cmTC_3f58e

Call Stack (most recent call first):
   share/cmake-3.14/Modules/CheckTypeSize.cmake:247 (__check_type_size_impl)
   CMakeLists.txt:362 (check_type_size)

--- SNIP ---

The problem is that the binary created by try_compile is located at 
libjpegturbo_library-ext-build/CMakeFiles/CMakeTmp/cmTC_3f58e.app, where 
cmake doesn't look. This happens with both the Unix Makefile and Ninja 
generators (since I don't use the Xcode generator I have no idea if it 
works there). The following patch to cmake fixes the problem:

--- SNIP ---

diff -uNr cmake-3.14.2.orig/Source/cmCoreTryCompile.cxx 
cmake-3.14.2/Source/cmCoreTryCompile.cxx
--- cmake-3.14.2.orig/Source/cmCoreTryCompile.cxx    2019-04-12 
14:10:08.000000000 +0200
+++ cmake-3.14.2/Source/cmCoreTryCompile.cxx    2019-04-15 
14:54:32.466161185 +0200
@@ -1040,8 +1040,12 @@
    }
    searchDirs.emplace_back("/Debug");
  #if defined(__APPLE__)
-  std::string app = "/Debug/" + targetName + ".app";
+  // When building for Darwin, iOS, etc., the test program may be an .app
+  // bundle, so look for those as well.
+  std::string app = "/" + targetName + ".app";
    searchDirs.push_back(std::move(app));
+  std::string appd = "/Debug/" + targetName + ".app";
+  searchDirs.push_back(std::move(appd));
  #endif
    searchDirs.emplace_back("/Development");

--- SNIP ---

So my question - is this a bug in CMake (the documentation says the 
Xcode generator is recommended, so I presume the other generators do not 
receive as much testing for iOS targets), or I am doing something 
fundamentally wrong ?

With kind regards,

Eric

-- 

*Dr. Eric Dönges *
Senior Software Engineer

MVTec Software GmbH | Arnulfstr. 205 | 80634 Munich | Germany
doenges at mvtec.com <mailto:doenges at mvtec.com> | Tel: +49 89 457 695-0 | 
www.mvtec.com <http://www.mvtec.com>

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