Support commands with executable targets

[sloretz]

This PR adds a new CMake function get_executable_path() and makes some ament_cmake functions that accept a command to execute use it.

The function checks if its argument is an executable target, and if so returns the appropriate property as a value or generator expression. This allows commands to be given executable targets in addition to paths.

Locally I tested this with

find_package(Python3 REQUIRED COMPONENTS Interpreter)
get_executable_path(py_imported_target_build Python3::Interpreter BUILD)
message(STATUS "py_imported_target_build ${py_imported_target_build}")
add_custom_target(genexdebug1 ALL COMMAND ${CMAKE_COMMAND} -E echo "py_imported_target_build: ${py_imported_target_build}")

set(PYTHON_EXECUTABLE "/usr/bin/python3")
get_executable_path(py_variable_build "${PYTHON_EXECUTABLE}" BUILD)
message(STATUS "py_variable_build ${py_variable_build}")
add_custom_target(genexdebug2 ALL COMMAND ${CMAKE_COMMAND} -E echo "py_variable_build: ${py_variable_build}")

get_executable_path(py_imported_target_config Python3::Interpreter CONFIGURE)
message(STATUS "py_imported_target_config ${py_imported_target_config}")

get_executable_path(py_variable_config "${PYTHON_EXECUTABLE}" CONFIGURE)
message(STATUS "py_variable_config ${py_variable_config}")

add_executable(foo foobar.cpp)
get_executable_path(py_exec_build "foo" BUILD)
message(STATUS "py_exec_build ${py_exec_build}")
add_custom_target(genexdebug3 ALL COMMAND ${CMAKE_COMMAND} -E echo "py_exec_build: ${py_exec_build}")

get_executable_path(py_exec_config "foo" CONFIGURE)
message(STATUS "py_exec_config ${py_exec_config}")

And the results were

$ cmake ..
-- py_imported_target_build $<TARGET_PROPERTY:Python3::Interpreter,LOCATION>
-- py_variable_build /usr/bin/python3
-- py_imported_target_config /home/osrf/projects/siws/env3/bin/python3
-- py_variable_config /usr/bin/python3
-- py_exec_build $<TARGET_FILE:foo>
CMake Warning at CMakeLists.txt:62 (message):
  There exists a non-imported executable target named 'foo', but those cannot
  be used at configure time.  Assuming it's a path instead.
Call Stack (most recent call first):
  CMakeLists.txt:96 (get_executable_path)


-- py_exec_config foo
-- Configuring done
-- Generating done
-- Build files have been written to: /home/osrf/tmp/cet/build
$ make
[100%] Built target foo
py_exec_build: /home/osrf/tmp/cet/build/foo
[100%] Built target genexdebug3
py_variable_build: /usr/bin/python3
[100%] Built target genexdebug2
py_imported_target_build: /home/osrf/projects/siws/env3/bin/python3
[100%] Built target genexdebug1

This is in support of ros2/python_cmake_module#6

[sloretz]

Full CI

• Linux
• Linux-aarch64
• macOS
• Windows

[nuclearsandwich]

This is the kind of thing where it feels like there ought to be a CMake built in for it but there's enough logic here that I wouldn't want it copied around everywhere it is needed.