Is there a cross-compiler method to disable coverage flags for test executables using CMake?

Question

I am creating a generic C++, CMake, and Catch project template that I plan on using in the future, and want to enable code coverage reports for it. To do so, I decided to add the following CMake module into my list of Modules: CodeCoverage.cmake. My usage for this essentially boils down to the following snippet:

if (ENABLE_COVERAGE AND NOT CMAKE_CONFIGURATION_TYPES)
    if (NOT CMAKE_BUILD_TYPE STREQUAL "Debug")
        message(STATUS "Coverage in a non-debug build may lead to misleading results! Setting build type to 'Debug'!")
        set(CMAKE_BUILD_TYPE "Debug" CACHE STRING "" FORCE)
    endif (NOT CMAKE_BUILD_TYPE STREQUAL "Debug")

    include(CodeCoverage)
    APPEND_COVERAGE_COMPILER_FLAGS()

    if (NOT BUILD_TESTS)
        message(STATUS "Tests must be enabled in a coverage build! Setting BUILD_TESTS to On!")
        set(BUILD_TESTS On CACHE STRING "" FORCE)
    endif (NOT BUILD_TESTS)

    set(COVERAGE_EXCLUDES 'tests/*')

    include(CodeCoverage)
    APPEND_COVERAGE_COMPILER_FLAGS()

    SETUP_TARGET_FOR_COVERAGE(NAME coverage EXECUTABLE tests DEPENDENCIES coverage)
else (ENABLE_COVERAGE AND NOT CMAKE_CONFIGURATION_TYPES)
    # ...
endif (ENABLE_COVERAGE AND NOT CMAKE_CONFIGURATION_TYPES)

Details.

• ENABLE_COVERAGE is command line flag which I use to enable/disable code coverage, which will be generated using lcov/gcov.

• tests is the name of my executable which runs all of my unit tests. First I use add_subdirectory to add its folder, and inside the folder I use:

  set(TEST_SOURCES test_hello_world.cpp test_factorial.cpp)
  
  add_executable(tests main.cpp ${TEST_SOURCES})
  target_link_libraries(tests Project-Name-lib)
  
  include(ParseAndAddCatchTests)
  ParseAndAddCatchTests(tests)
  

My problem:

When I usually run my make script, the code compiles with ease, including the test executable which takes ~10 seconds to build. However, when I enable coverage for my code, the code gets stuck on building main.cpp.o (Inside tests), and make never finishes. When I run make VERBOSE=1, I get the following command which is being run for said object:

cd project_dir/build/tests && /usr/bin/g++-5 
    -g -O0 --coverage -fprofile-arcs -ftest-coverage -g -O0 
    --coverage -fprofile-arcs -ftest-coverage -g 
    -I/project_dir/include -I/project_dir/build    
    -std=c++14 -o CMakeFiles/tests.dir/main.cpp.o -c /project_dir/main.cpp

(I have shortened some of the paths for readability and indented lines are part of the same command)

Apparently, even with set(COVERAGE_EXCLUDES 'tests/*'), the compiler is still appending the coverage flags to the test executable, which I think is the source of the slow build time. If my conclusion is correct, then how can I tell the compiler to not add these flags to my test executable? If my conclusion is incorrect, then how can I reduce the build time for this executable? (I don't want to directly mention flag names, since that might not work across all compilers(By which I mean GCC/Clang))

On a side note, my main.cpp contains:

#define CATCH_CONFIG_MAIN
#include "catch.hpp"

And a sample test file contains:

#include <project-abbr/factorial.hpp>
#include "catch.hpp"

TEST_CASE("function factorial")
{
    SECTION("normal arguments")
    {
        REQUIRE(factorial(2) == 2);
        REQUIRE(factorial(3) == 6);
        REQUIRE(factorial(4) == 24);
        REQUIRE(factorial(5) == 120);
    }
}

Answer 1

UPDATE

The following code isn't really a solution. It works only for all functions that are defined only in source files. Meaning if you had a template library or a header only library, then this solution is completely useless. The true solution is to call the function append_coverage_compiler_flags which allows for complete coverage. However, this may cause a compilation freeze, as shown in the OP's post...

---

Ok, I experimented a bit, looked at the documentation, and found a solution which isn't really optimal but works nonetheless. I used the function target_compile_options to only add the coverage flags to the targets I want instead of the function ADD_COVERAGE_COMPILE_FLAGS() from the module, as follows:

if (NOT CMAKE_BUILD_TYPE STREQUAL "Debug")
    message(STATUS "Coverage in a non-debug build may lead to misleading results! Setting build type to 'Debug'!")
    set(CMAKE_BUILD_TYPE "Debug" CACHE STRING "" FORCE)
endif (NOT CMAKE_BUILD_TYPE STREQUAL "Debug")

include(CodeCoverage)

if (NOT BUILD_TESTS)
    message(STATUS "Tests must be enabled in a coverage build! Setting BUILD_TESTS to On!")
    set(BUILD_TESTS On CACHE STRING "" FORCE)
endif (NOT BUILD_TESTS)

set(COVERAGE_EXCLUDES 'tests/*')

include(CodeCoverage)

include_directories(include ${PROJECT_BINARY_DIR})
add_subdirectory(src)

target_compile_options(Project-Name-lib PRIVATE "--coverage")
target_compile_options(Project-Name PRIVATE "--coverage")

SETUP_TARGET_FOR_COVERAGE(NAME coverage EXECUTABLE tests DEPENDENCIES coverage)

There is a caveat to this solution. Apparently, header files are not included in the code coverage...