How do I make build rules in cmake to preprocess lazy C++ .lzz files that generate .h and .cpp files?

Question

What I\'d like to do is write just Lazy C++ .lzz files and then have lzz run before a build to generate .cpp and .h files that will be built into the final application, sort

Answer 1

Here is an example of how to do this... First you need to find the lzz program, for that use the find_program command:

find_program(LZZ_COMMAND lzz)

This sets LZZ_COMMAND to the path of the compiler. Then use a CMake custom command to compile the LZZ file to their C++ header/implementation files:

add_custom_command(
    OUTPUT ${output}
    COMMAND ${LZZ_COMMAND} -o ${CMAKE_CURRENT_BINARY_DIR} ${filename})

That generates the files in the current build directory, in case you do out-of-source builds. You will also need to specify that the outputs are generated files:

set_source_files_properties(${output} PROPERTIES GENERATED TRUE)

Put that all together and you get a CMakeLists.txt file something like this:

cmake_minimum_required(VERSION 2.8)
project(lazy_test)
find_program(LZZ_COMMAND lzz)
function(lazy_compile filename)
    get_filename_component(base ${filename} NAME_WE)
    set(base_abs ${CMAKE_CURRENT_BINARY_DIR}/${base})
    set(output ${base_abs}.cpp ${base_abs}.h)
    add_custom_command(
        OUTPUT ${output}
        COMMAND ${LZZ_COMMAND} -o ${CMAKE_CURRENT_BINARY_DIR} ${filename})
    set_source_files_properties(${output} PROPERTIES GENERATED TRUE)
endfunction()
lazy_compile(${CMAKE_CURRENT_SOURCE_DIR}/example.lzz)
add_executable(test example.cpp example.h)

You would probably also want to add include path and other options to lzz eventually. If you placed all the Lazy C++ stuff into a module file and included that from the CMakeLists.txt it would be a bit cleaner. But this is the basic idea.