How to check if a module included with `include(...)` by cmake, exists? - cmake

Question

In one of my CMakeLists.txt file I do:
include( AICxxProject )
and under certain circumstances (wrong installation) this gives:
CMake Error at src/CMakeLists.txt:1 (include):
include could not find load file:
AICxxProject
I'd like to tell the user what they did wrong and how to fix it
with a FATAL_ERROR message. But, how can I detect if a module
like AICxxProject is going to be found before include-ing it?

Answer 1

Solved by actually reading the documentation of include.
The following works,
include( AICxxProject OPTIONAL RESULT_VARIABLE _module_path )
if ( NOT _module_path )
message( FATAL_ERROR
"include could not find load file: AICxxProject\n"
"1) Make sure that you have the git submodule https://github.com/CarloWood/cwm4 in the top-level directory.\n"
"2) Use `include(cwm4/cmake/AICxxProject)` right below the `project(...)` command in your top-level CMakeLists.txt."
)
endif ()
with as output
CMake Error at cwds/CMakeLists.txt:9 (message):
include could not find load file: AICxxProject
1) Make sure that you have the git submodule
https://github.com/CarloWood/cwm4 in the top-level directory.
2) Use `include(cwm4/cmake/AICxxProject)` right below the `project(...)`
command in your top-level CMakeLists.txt.
-- Configuring incomplete, errors occurred!