create_distro.cmake

# Copyright (c) 2021 ARM Limited. All rights reserved.
# SPDX-License-Identifier: Apache-2.0

# This script provides mbed_create_distro(), a function that lets you compile multiple
# apps that use Mbed OS without waiting for Mbed OS to build multiple times.

# You can use it like this:
# mbed_create_distro(mbed_for_my_app mbed-os mbed-storage-kvstore mbed-storage-filesystem)
#
# add_executable(myapp1 MyApp1.cpp)
# target_link_libraries(myapp1 PRIVATE mbed_for_my_app)
# mbed_set_post_build(myapp1)
#
# add_executable(myapp2 MyApp2.cpp)
# target_link_libraries(myapp2 PRIVATE mbed_for_my_app)
# mbed_set_post_build(myapp2)
#
# Both myapp1 and myapp2 will act like they were linked to mbed-os, mbed-storage-kvstore,
# and mbed-storage-filesystem.  Note that if you actually did target_link_libraries(myapp1 PRIVATE mbed-os
# mbed-storage-kvstore mbed-storage-filesystem), it would compile a new version of the Mbed OS source
# files for each target. However, using mbed_create_distro(), Mbed OS will only be compiled once.

# Append the value of PROPERTY from SOURCE to the value of PROPERTY on DESTINATION
function(copy_append_property PROPERTY SOURCE DESTINATION)
	get_property(PROP_IS_DEFINED TARGET ${SOURCE} PROPERTY ${PROPERTY} SET)
	if(PROP_IS_DEFINED)
		get_property(PROP_VALUE TARGET ${SOURCE} PROPERTY ${PROPERTY})
		set_property(TARGET ${DESTINATION} APPEND PROPERTY ${PROPERTY} "${PROP_VALUE}")
	endif()
endfunction(copy_append_property)

# Create a "distribution" of Mbed OS containing the base Mbed and certain modules.
# This distribution only needs to be compiled once and can be referenced in an arbitrary amount of targets.
function(mbed_create_distro NAME) # ARGN: modules...
	add_library(${NAME} OBJECT)
	mbed_configure_app_target(${NAME})

	# First link as private dependencies
	target_link_libraries(${NAME} PRIVATE ${ARGN})

	# Now copy include dirs, compile defs, and compile options (but NOT interface source files) over
	# to the distribution target so they will be passed into things that link to it.
	# To do this, we need to recursively traverse the tree of dependencies.
	set(REMAINING_MODULES ${ARGN})
	set(COMPLETED_MODULES ${ARGN})
	while(NOT "${REMAINING_MODULES}" STREQUAL "")

		list(GET REMAINING_MODULES 0 CURR_MODULE)

		copy_append_property(INTERFACE_COMPILE_DEFINITIONS ${CURR_MODULE} ${NAME})
		copy_append_property(INTERFACE_COMPILE_OPTIONS ${CURR_MODULE} ${NAME})
		copy_append_property(INTERFACE_INCLUDE_DIRECTORIES ${CURR_MODULE} ${NAME})
		copy_append_property(INTERFACE_LINK_OPTIONS ${CURR_MODULE} ${NAME})

		list(REMOVE_AT REMAINING_MODULES 0)
		list(APPEND COMPLETED_MODULES ${CURR_MODULE})

		# find sub-modules of this module
		get_property(SUBMODULES TARGET ${CURR_MODULE} PROPERTY INTERFACE_LINK_LIBRARIES)
		foreach(SUBMODULE ${SUBMODULES})
			if(NOT "${SUBMODULE}" MATCHES "::@") # remove CMake internal CMAKE_DIRECTORY_ID_SEP markers
				if(NOT ${SUBMODULE} IN_LIST COMPLETED_MODULES)
					list(APPEND REMAINING_MODULES ${SUBMODULE})
				endif()
			endif()
		endforeach()

	endwhile()

endfunction(mbed_create_distro)