CMake ignoring CMAKE_MODULE_PATH - cmake

Question

I'm having trouble getting CMake's include() statement to recognize CMAKE_MODULE_PATH. I'm hoping to do something like this:
list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
include(Foo.cmake)
with this style of directory tree:
.
├── cmake
│   └── Foo.cmake
├── CMakeLists.txt
However, I get the error:
include could not find load file:
Foo.cmake
Based on the docs for include() and CMAKE_MODULE_PATH, I thought that this should be possible.
If I keep the same tree but modify the include, it loads fine:
include(cmake/Foo.cmake)
Am I mistaken or doing something wrong?
Thanks!

Answer 1

It should be a module name - without .cmake extension - for apply CMAKE_MODULE_PATH variable when search the file with include command:
# This searches a *module* and uses 'CMAKE_MODULE_PATH' variable
include(Foo)
# This searches a *file* and doesn't use 'CMAKE_MODULE_PATH' variable
include(Foo.cmake)
The signature of include function
include(<file|module> [OPTIONAL] [RESULT_VARIABLE ]
[NO_POLICY_SCOPE])
means that its first argument could be either a file or a module.
And CMAKE_MODULE_PATH variable is applied only when search a module:
If a module is specified instead of a file, the file with name <modulename>.cmake is searched first in CMAKE_MODULE_PATH, then in the CMake module directory.
The name of the file - <modulename>.cmake - suggests that module name shouldn't have .cmake suffix.