CMAKE_SOURCE_DIR
----------------

The path to the top level of the source tree.

This is the full path to the top level of the current CMake source
tree.  For an in-source build, this would be the same as
:variable:`CMAKE_BINARY_DIR`.

When run in ``-P`` script mode, CMake sets the variables
:variable:`CMAKE_BINARY_DIR`, :variable:`CMAKE_SOURCE_DIR`,
:variable:`CMAKE_CURRENT_BINARY_DIR` and
:variable:`CMAKE_CURRENT_SOURCE_DIR` to the current working directory.
