CPack: only pack files tracked by git

I'm trying to understand how to use CPack. I want to produce a binary and a source package. The binary one is perfectly fine, including only what's necessary. In the source distribution, though, there are basically all files present in the project's root directory - including my CMake build directory from where I ran the CPack command.

Since one might have several build directories, I can't see how I can exclude them all from being put into the source package.

set(CPACK_SOURCE_IGNORE_FILES "*.git*") works fine but ideally I would like to restrict the set of included files only to those that are tracked by version control, e.g. git, in the first place. And, no, I don't consider making sure that my project directory is completely clean before a cpack a viable option.

(Packing an entire directory into an archive is something I don't need CPack for.)

Solution

This is possible with CPACK_PROJECT_CONFIG_FILE. This file is executed by cpack before the CPACK_* variables are queried, so you can use this file to dynamically add entries to the CPACK_SOURCE_IGNORE_FILES list.

In the top-level CMakeLists.txt add the following before the call to include(CPack):

find_package(Git)
configure_file(
  "${CMAKE_SOURCE_DIR}/ProjectCPackConfig.cmake.in"
  "${CMAKE_BINARY_DIR}/ProjectCPackConfig.cmake"
  @ONLY
)
set(CPACK_PROJECT_CONFIG_FILE "${CMAKE_BINARY_DIR}/ProjectCPackConfig.cmake")

And create ProjectCPackConfig.cmake.in:

# If we are packaging source, then ignore files that are untracked by git.
if(CPACK_TOPLEVEL_TAG STREQUAL CPACK_SOURCE_TOPLEVEL_TAG AND "@GIT_FOUND@")
  # Use `git ls-files` to list untracked files/directories
  execute_process(
    COMMAND "@GIT_EXECUTABLE@" ls-files --ignored --other --exclude-standard --directory
    WORKING_DIRECTORY "@CMAKE_SOURCE_DIR@"
    RESULT_VARIABLE status
    OUTPUT_VARIABLE GIT_IGNORED_FILES
    OUTPUT_STRIP_TRAILING_WHITESPACE
  )
  if(NOT status EQUAL 0)
    message(ERROR "Failed to query git for file ignore list.")
  endif()

  # split the output of git ls-files into a list
  string(REPLACE "\n" ";" GIT_IGNORED_FILES "${GIT_IGNORED_FILES}")

  # .git directory is implicitly untracked
  list(APPEND GIT_IGNORED_FILES ".git/")

  foreach(IGN_FILE ${GIT_IGNORED_FILES})
    # apply escaping to the filename so nothing is mistaken for a regex quantifier
    string(REGEX REPLACE "." "\\\\\\0" IGN_FILE_QUOTED "@CMAKE_SOURCE_DIR@/${IGN_FILE}")

    # add the quoted filename to the CPACK_IGNORE_FILES list
    list(APPEND CPACK_IGNORE_FILES "^${IGN_FILE_QUOTED}")
  endforeach()
endif()

It is worth noting that cpack does not directly use any CPACK_SOURCE_* variables. Instead, CPACK_SOURCE_* values are assigned to CPACK_* variables in CMAKE_BINARY_DIR/CPackSourceConfig.cmake, and cpack executes this file before executing CMAKE_BINARY_DIR/ProjectCPackConfig.cmake. This is why I assign to CPACK_IGNORE_FILES instead of CPACK_SOURCE_IGNORE_FILES, and it is also why I use CPACK_TOPLEVEL_TAG STREQUAL CPACK_SOURCE_TOPLEVEL_TAG to detect whether a source package is currently being generated.