cmake: Provide a way to deal with generated files in gtest_add_tests

Generated files don't exist yet, so they can't just be passed to
file(READ). Unfortunately, the GENERATED property doesn't help
that much here, since it is only visible to lists in the same
directory as the relevant source file. Since we call gtest_add_tests
at the toplevel CMakeLists.txt, it won't be visible.

Generated files which form part of the tests but don't contain
any tests themselves should be put into SUPPORT_SOURCES before
core_add_test is called. In that case, they won't be considered
as part of the library.

project/cmake/scripts/common/macros.cmake

@@ -41,9 +41,12 @@ endfunction()
 
 # Add a test library, and add sources to list for gtest integration macros
 function(core_add_test_library name)
+  # Backup the old SOURCES variable, since we'll append SUPPORT_SOURCES to it
+  set(TEST_ONLY_SOURCES ${SOURCES})
+  set(SOURCES ${SOURCES} ${SUPPORT_SOURCES})
   core_add_library(${name} NO_MAIN_DEPENDS)
   set_target_properties(${name} PROPERTIES EXCLUDE_FROM_ALL 1)
-  foreach(src ${SOURCES})
+  foreach(src ${TEST_ONLY_SOURCES})
     # This will prepend CMAKE_CURRENT_SOURCE_DIR if the path is relative,
     # otherwise use the absolute path.
     get_filename_component(src_path "${src}" ABSOLUTE)

project/cmake/scripts/common/projectmacros.cmake

@@ -54,6 +54,9 @@ function(GTEST_ADD_TESTS executable extra_args)
         message(FATAL_ERROR "Missing ARGN: Read the documentation for GTEST_ADD_TESTS")
     endif()
     foreach(source ${ARGN})
+        # This assumes that every source file passed in exists. Consider using
+        # SUPPORT_SOURCES for source files which do not contain tests and might
+        # have to be generated.
         file(READ "${source}" contents)
         string(REGEX MATCHALL "TEST_?[F]?\\(([A-Za-z_0-9 ,]+)\\)" found_tests ${contents})
         foreach(hit ${found_tests})