mbed_create_distro() reborn: a function to make adding multiple targets easy

tools/cmake/app.cmake

@@ -61,3 +61,6 @@ else()
     message(STATUS "Missing Python dependencies (python3, intelhex, prettytable) so the memory map cannot be printed")
 endif()
 
+# load mbed_create_distro
+include(${CMAKE_CURRENT_LIST_DIR}/create_distro.cmake)
+

tools/cmake/create_distro.cmake

@@ -0,0 +1,70 @@
+# 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)

tools/cmake/mbed_set_linker_script.cmake

@@ -3,6 +3,7 @@
 
 #
 # Preprocesses and sets the linker script for an Mbed target.
+# Called once for each MCU target in the build system.
 #
 function(mbed_set_linker_script input_target raw_linker_script_path)
     set(LINKER_SCRIPT_PATH ${CMAKE_CURRENT_BINARY_DIR}/${input_target}.link_script.ld)