How to omit debug info for a single source file? - cmake

Question

I'm writing a test for a tool that parses debug info, and I would like to omit debug info for a single compilation unit (source file) in my debug target. Is there any way to accomplish this with cmake?
Obviously, I could just hardcode the compiler flags, but I'd like to keep my build portable across different OSes and toolchains (say gnu and msvc).
Changing CMAKE_BUILD_TYPE on the fly doesn't seem to work.

Answer 1

To do this you have to modify the default flags because with multi-configuration generators you can't force a specific build type. This is a just a quick example to show how to remove the debug flag from the defaults and then add it back in. You can then update this example to use a variable to collect all the source files and some if statements to check which compiler is being used to test for either -g or /Zi.
cmake_minimum_required(VERSION 3.12)
project(sample)
message( "\${CMAKE_CXX_FLAGS_RELEASE} = ${CMAKE_CXX_FLAGS_RELEASE}")
message( "\${CMAKE_CXX_FLAGS_DEBUG} = ${CMAKE_CXX_FLAGS_DEBUG}")
string(REPLACE "-g" "" CMAKE_CXX_FLAGS_DEBUG ${CMAKE_CXX_FLAGS_DEBUG})
string(REPLACE "/Zi" "" CMAKE_CXX_FLAGS_DEBUG ${CMAKE_CXX_FLAGS_DEBUG})
string(REPLACE "-g" "" CMAKE_CXX_FLAGS_RELWITHDEBINFO ${CMAKE_CXX_FLAGS_RELWITHDEBINFO})
string(REPLACE "/Zi" "" CMAKE_CXX_FLAGS_RELWITHDEBINFO ${CMAKE_CXX_FLAGS_RELWITHDEBINFO})
message( "\${CMAKE_CXX_FLAGS_DEBUG} = ${CMAKE_CXX_FLAGS_DEBUG}")
message( "\${CMAKE_CXX_FLAGS_RELWITHDEBINFO} = ${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
set_source_files_properties(file1.cpp PROPERTIES COMPILE_FLAGS "/Zi")
add_executable( sample file1.cpp file2.cpp )

Answer 2

You can access the default compile flags that cmake uses per configuration (see this answer). You can also set the COMPILE_FLAGS property on any source file. Thus, after you have created a target, it should be as simple as querying the default compile options for your language, and applying the appropriate defaults using set_source_files_properties.
For example, here's a CMakeLists.txt for an extremely simple project:
cmake_minimum_required(VERSION 3.6.1)
project(MyProj)
set_source_files_properties(file1.cpp PROPERTIES COMPILE_FLAGS ${CMAKE_CXX_FLAGS_RELEASE})
get_source_file_property(FILE1_FLAGS file1.cpp COMPILE_FLAGS)
get_source_file_property(FILE2_FLAGS file2.cpp COMPILE_FLAGS)
message( "\${FILE1_FLAGS} = ${FILE1_FLAGS}")
message( "\${FILE2_FLAGS} = ${FILE2_FLAGS}")
add_executable( MyExe file1.cpp file2.cpp )
Which outputs (for MSVC):
${FILE1_FLAGS} = /MD /O2 /Ob2 /DNDEBUG
${FILE2_FLAGS} = NOTFOUND
If you inspect the generated MyExe.vcxproj, you'll see that defaults are used to compile file2.cpp, whereas for file1.cpp, all the configurations use release settings:
<ClCompile Include="C:\temp\cmake\file1.cpp">
<InlineFunctionExpansion Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">AnySuitable</InlineFunctionExpansion>
<Optimization Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">MaxSpeed</Optimization>
<RuntimeLibrary Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">MultiThreadedDLL</RuntimeLibrary>
<PreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
<InlineFunctionExpansion Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">AnySuitable</InlineFunctionExpansion>
<Optimization Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">MaxSpeed</Optimization>
<RuntimeLibrary Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">MultiThreadedDLL</RuntimeLibrary>
<PreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
<InlineFunctionExpansion Condition="'$(Configuration)|$(Platform)'=='MinSizeRel|Win32'">AnySuitable</InlineFunctionExpansion>
<Optimization Condition="'$(Configuration)|$(Platform)'=='MinSizeRel|Win32'">MaxSpeed</Optimization>
<RuntimeLibrary Condition="'$(Configuration)|$(Platform)'=='MinSizeRel|Win32'">MultiThreadedDLL</RuntimeLibrary>
<PreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='MinSizeRel|Win32'">NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
<InlineFunctionExpansion Condition="'$(Configuration)|$(Platform)'=='RelWithDebInfo|Win32'">AnySuitable</InlineFunctionExpansion>
<Optimization Condition="'$(Configuration)|$(Platform)'=='RelWithDebInfo|Win32'">MaxSpeed</Optimization>
<RuntimeLibrary Condition="'$(Configuration)|$(Platform)'=='RelWithDebInfo|Win32'">MultiThreadedDLL</RuntimeLibrary>
<PreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='RelWithDebInfo|Win32'">NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
</ClCompile>
<ClCompile Include="C:\temp\cmake\file2.cpp" />
I haven't tried this on other generators, but it should work identically.