CMake: Modify install_python_package() so it keeps the build-dir copy up-to-date too

cmake/scripts/CopyPython.cmake

@@ -0,0 +1,78 @@
+# Filename: CopyPython.cmake
+#
+# Description: When run, copies Python files from a source directory to a
+#   build directory located somewhere in the project's binary path. If
+#   PYTHON_EXECUTABLES is provided, it will also invoke compileall in the
+#   destination dir(s) to precache .pyc/.pyo files.
+#
+# Usage:
+#   This script is invoked via add_custom_target, like this:
+#   cmake -D OUTPUT_DIR="/out/dir/Release"
+#         -D SOURCE_DIR="/panda3d/direct/src/"
+#         -D PYTHON_EXECUTABLES="/usr/bin/python3.6"
+#         -P CopyPython.cmake
+#
+
+if(NOT CMAKE_SCRIPT_MODE_FILE)
+  message(FATAL_ERROR "CopyPython.cmake should not be included but run in script mode.")
+  return()
+endif()
+
+if(NOT DEFINED OUTPUT_DIR)
+  message(FATAL_ERROR "OUTPUT_DIR should be defined when running CopyPython.cmake!")
+  return()
+endif()
+
+# Ensure OUTPUT_DIR exists
+file(MAKE_DIRECTORY ${OUTPUT_DIR})
+
+# If there's a SOURCE_DIR, glob for .py files and copy
+# (this is done by hand to avoid the CMake bug where it creates empty dirs)
+if(DEFINED SOURCE_DIR)
+  file(GLOB_RECURSE py_files RELATIVE "${SOURCE_DIR}" "${SOURCE_DIR}/*.py")
+  foreach(py_file ${py_files})
+    get_filename_component(py_file_parent "${py_file}" DIRECTORY)
+    if(NOT EXISTS "${SOURCE_DIR}/${py_file_parent}/__init__.py")
+      # The source file isn't part of a Python package, even though it is a .py
+      # file. Skip it.
+      continue()
+    endif()
+
+    file(TIMESTAMP "${SOURCE_DIR}/${py_file}" src_stamp)
+    file(TIMESTAMP "${OUTPUT_DIR}/${py_file}" dst_stamp)
+
+    if(NOT src_stamp STREQUAL dst_stamp)
+      file(COPY "${SOURCE_DIR}/${py_file}" DESTINATION "${OUTPUT_DIR}/${py_file_parent}")
+      set(changed YES)
+    endif()
+
+  endforeach(py_file)
+
+else()
+  # No SOURCE_DIR; assume we're outdated since our caller might be populating
+  # the OUTPUT_DIR themselves
+  set(changed YES)
+
+endif()
+
+# Make sure Python recognizes OUTPUT_DIR as a package
+if(NOT EXISTS "${OUTPUT_DIR}/__init__.py")
+  file(WRITE "${OUTPUT_DIR}/__init__.py" "")
+  set(changed YES)
+endif()
+
+# Generate .pyc files for each Python version, if our caller wants
+if(changed AND DEFINED PYTHON_EXECUTABLES)
+  foreach(interp ${PYTHON_EXECUTABLES})
+    execute_process(
+      COMMAND "${interp}" -m compileall .
+      OUTPUT_QUIET
+      WORKING_DIRECTORY "${OUTPUT_DIR}")
+
+    execute_process(
+      COMMAND "${interp}" -OO -m compileall .
+      OUTPUT_QUIET
+      WORKING_DIRECTORY "${OUTPUT_DIR}")
+
+  endforeach(interp)
+endif()