In CMake, how can I find the directory of an included file?

People have reported seemingly contradictory facts about how CMAKE_CURRENT_LIST_DIR behaves. Now I know the reason for the confusion:

First, in my Linux environment:

$ cd /path/to/home  
$ mkdir cmake-test  
$ cd cmake-test  
$ mkdir source  
$ mkdir source/subdirectory  
$ mkdir build  

I create these two files:

$ cat source/CMakeLists.txt  
include(subdirectory/foo.cmake)  

$ cat source/subdirectory/foo.cmake  
message("CMAKE_CURRENT_LIST_DIR is ${CMAKE_CURRENT_LIST_DIR}")  

CMake works as reported by Fraser and Robert Dailey:

$ cd build  
$ cmake ../source  
CMAKE_CURRENT_LIST_DIR is /path/to/home/cmake-test/source/subdirectory  
[...]  

However, I add a function to foo.cmake, which I call from CMakeLists.txt:

$ cat ../source/subdirectory/foo.cmake  
message("CMAKE_CURRENT_LIST_DIR is ${CMAKE_CURRENT_LIST_DIR}")  
function(bar)  
    message("CMAKE_CURRENT_LIST_DIR in bar() is ${CMAKE_CURRENT_LIST_DIR}")  
endfunction()  

$ cat ../source/CMakeLists.txt  
include(subdirectory/foo.cmake)  
bar()  

Then:

$ cmake ../source  
CMAKE_CURRENT_LIST_DIR is /path/to/home/cmake-test/source/subdirectory  
CMAKE_CURRENT_LIST_DIR in bar() is /path/to/home/cmake-test/source  
[...]  

So, the value of CMAKE_CURRENT_LIST_DIR in foo.cmake is not the same at the time foo.cmake is included and when bar() is called. This is according to the specification of CMAKE_CURRENT_LIST_DIR.

Here is one possible solution for accessing the directory of foo.cmake from within bar():

$ cat ../source/subdirectory/foo.cmake  
set(DIR_OF_FOO_CMAKE ${CMAKE_CURRENT_LIST_DIR})  
function(bar)  
    message("DIR_OF_FOO_CMAKE in bar() is ${DIR_OF_FOO_CMAKE}")  
endfunction()  

after which I get the behavior I was looking for:

$ cmake ../source  
DIR_OF_FOO_CMAKE in bar() is /path/to/home/cmake-test/source/subdirectory  
[...]