[libcxx] PR26777 Fix tests when built with CXX="ccache clang++"

[hintonda]

Summary

If you use ccache to build libcxx by setting CXX="ccache
clang++", check-libcxx will fail since LIBCXX_COMPILER will be set to
"ccache".

We can't just include CMAKE_CXX_COMPILER_ARG1 because of a python
parsing issue, so the best we can do right now is to use
CMAKE_CXX_COMPILER_ARG1 if it exists, and CMAKE_CXX_COMPILER if it
doesn't.

[EricWF]

I appreciate the patch, handling 'ccache' is a good thing to have. I'll look at this again once the inline comment is addressed.

CMakeLists.txt

225

What if somebody uses CXX='clang++ --foo'. It seems incorrect to handle ccache in this way. Instead I would rather we

1. Check if 'ARG1' is present.
2. If so attempt to find the string 'ccache' within 'CMAKE_CXX_COMPILER'
3. Only if we manage to match it do we use 'CMAKE_CXX_COMPILER_ARG1' as 'LIBCXX_COMPILER'.

[hintonda]

If *_COMPILER_ARG1 is set, then it shall be the compiler, and the value for CMAKE_<LANG>_COMPILER may be ccache, but could also be something else, e.g., distcc, etc. Therefore, I don't see a clean way to check it.

However, newer versions of cmake have abandoned the *_COMPILER_ARG1 solutions and set CMAKE_<LANG>_COMPILER to the real compiler and use a new variable, CMAKE_<LANG>_COMPILER_LAUNCHER for ccache, distcc, etc..

So the solution is just to upgrade to the newest version of cmake if you want to use ccache, etc...

[EricWF]

OK. Thanks for the update. Sorry we couldn't land this.

CMakeLists.txt

if (LIBCXX_HAS_MUSL_LIBC AND NOT LIBCXX_INSTALL_SUPPORT_HEADERS)
   message(FATAL_ERROR "LIBCXX_INSTALL_SUPPORT_HEADERS can not be turned off"
                       "when building for Musl with LIBCXX_HAS_MUSL_LIBC.")
 endif()
 
 #===============================================================================
 # Configure System
 #===============================================================================
 
-set(LIBCXX_COMPILER    ${CMAKE_CXX_COMPILER})
+# When ccache is used, the actual compiler will be in arg1.  Solves
+# a python parsing issue in CXXCompiler() where parameters with spaces are
+# treated as seperate parameters.
+if(CMAKE_CXX_COMPILER_ARG1)
+  string(STRIP ${CMAKE_CXX_COMPILER_ARG1} LIBCXX_COMPILER )
+else()
+  set(LIBCXX_COMPILER ${CMAKE_CXX_COMPILER})
+endif()
 set(LIBCXX_SOURCE_DIR  ${CMAKE_CURRENT_SOURCE_DIR})
 set(LIBCXX_BINARY_DIR  ${CMAKE_CURRENT_BINARY_DIR})
 set(LIBCXX_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXX_LIBDIR_SUFFIX})
 
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LIBCXX_LIBRARY_DIR})
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${LIBCXX_LIBRARY_DIR})
 
 # Declare libc++ configuration variables.