How to add in a CMake project a global file extension (*.pde) to GCC which is treated like C++ code

Question

I have a very simple CMake script. Unfortunately, the project uses a *.pde file which is plain C++ or C code.

CMake is working with any file ending, but I get a comp

Answer 1

You should be able to use set_source_files_properties along with the LANGUAGE property to mark the file(s) as C++ sources:

set_source_files_properties(${TheFiles} PROPERTIES LANGUAGE CXX)

As @steveire pointed out in his own answer, this bug will require something like the following workaround:

set_source_files_properties(${TheFiles} PROPERTIES LANGUAGE CXX)
if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
  add_definitions("-x c++")
endif()

Answer 2

CMake doesn't do this for you:

http://public.kitware.com/Bug/view.php?id=14516

Answer 3

Normally you should be able to just extend CMAKE_CXX_SOURCE_FILE_EXTENSIONS. This would help, if you have a lot of files with unknown file extensions.

But this variable is not cached - as e.g. CMAKE_CXX_FLAGS is - so the following code in CMakeCXXCompiler.cmake.in will always overwrite/hide whatever you will set:

set(CMAKE_CXX_IGNORE_EXTENSIONS inl;h;hpp;HPP;H;o;O;obj;OBJ;def;DEF;rc;RC)
set(CMAKE_CXX_SOURCE_FILE_EXTENSIONS C;M;c++;cc;cpp;cxx;mm;CPP)

I consider this non-caching being a bug in CMake, but until this is going to be changed I searched for a workaround considering the following:

• You normally don't want to change files in your CMake's installation
• It won't have any effect if you change CMAKE_CXX_SOURCE_FILE_EXTENSIONS after project()/enable_language() (as discussed here).

I have successfully tested the following using one of the "hooks"/configuration variables inside CMakeCXXCompiler.cmake.in:

cmake_minimum_required(VERSION 2.8)

set(CMAKE_CXX_SYSROOT_FLAG_CODE "list(APPEND CMAKE_CXX_SOURCE_FILE_EXTENSIONS pde)")

project(RPiCopter CXX)

message("CMAKE_CXX_SOURCE_FILE_EXTENSIONS ${CMAKE_CXX_SOURCE_FILE_EXTENSIONS}")

add_executable(RPiCopter tinycopter.pde)

Answer 4

I decided to use this approach. I just remove the file ending by cmake in the temporary build directory. So GCC is not confused anymore because of the strange Arduino *.pde file extension.

# Exchange the file ending of the Arduino project file
configure_file(${CMAKE_CURRENT_SOURCE_DIR}/tinycopter.pde ${CMAKE_CURRENT_BINARY_DIR}/tinycopter.cpp)