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

For make:

sourcecode.h sourcecode.cpp: sourcecode.lzz
<TAB>lazy-cpp sourcecode.lzz

fill in sourcecode.h, sourcecode.cpp, and lazy-cpp with the correct values. I don't know them.

Answer 2

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.

Answer 3

I just wanted to share my CMakeLists.txt, which builds upon richq's script. The *.cpp and *.hpp files now properly depend on the *.lzz files. The *.lzz files are added to the project (which answers absense's question above) but kept separate from the generated files using the source_group command.

The only remaining dealbreaker for me is the inability to compile the current file for *.lzz files.

cmake_minimum_required(VERSION 2.8)

PROJECT(LzzTest)

find_program(LZZ_COMMAND lzz.exe)

# Syntax: 
#   add_lzz_file(<output> <lzz file>)
# Adds a build rule for the specified lzz file. The absolute paths of the generated 
# files are added to the <output> list. The files are generated in the binary dir.
# 
# TODO: Support for generating template files etc.
function(add_lzz_file output filename)
  # Only process *.lzz files
  get_filename_component(ext ${filename} EXT)
  if(NOT ext STREQUAL ".lzz")
    return()
  endif()

  set(header_extension "hpp")
  get_filename_component(base ${filename} NAME_WE)
  set(base_abs ${CMAKE_CURRENT_BINARY_DIR}/${base})
  set(outfiles ${base_abs}.cpp ${base_abs}.${header_extension})
  set(${output} ${${output}} ${outfiles} PARENT_SCOPE)

  #message("outfiles=${outfiles}, DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/${filename}")
  add_custom_command(
    OUTPUT ${outfiles}
    COMMAND ${LZZ_COMMAND} 
      -o ${CMAKE_CURRENT_BINARY_DIR} # output dir
      -hx ${header_extension}
      -sl -hl -il -tl -nl -x # insert #line commands w/ absolute paths
      -sd -hd -id -td -nd # don't output files that didn't change
      ${CMAKE_CURRENT_SOURCE_DIR}/${filename}
    DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/${filename}"
  )

  set_source_files_properties(${outfiles} PROPERTIES GENERATED TRUE)
endfunction()

include_directories(${CMAKE_CURRENT_BINARY_DIR})

set(SOURCES
  A.lzz
  B.lzz
  main.cpp
)

foreach(file ${SOURCES})
  add_lzz_file(GENERATED_SOURCES ${file})
endforeach()

source_group("" FILES ${SOURCES})
source_group(generated FILES ${GENERATED_SOURCES})

add_executable(LzzTest ${SOURCES} ${GENERATED_SOURCES})