Remove python_cmake_module and set hints (#204)

* Stop using python_cmake_module.

We really don't need it anymore, and can just use the
builtin find_package(Python3).

* Set hints to find the python version we actually want.

The comment in the commit explains the reasoning behind it.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

Author: clalancette

rosidl_generator_py/CMakeLists.txt

@@ -22,9 +22,6 @@ if(BUILD_TESTING)
 
   find_package(test_interface_files REQUIRED)
 
-  find_package(python_cmake_module REQUIRED)
-  find_package(PythonExtra MODULE REQUIRED)
-
   include(cmake/register_py.cmake)
   include(cmake/rosidl_generator_py_get_typesupports.cmake)
 

rosidl_generator_py/cmake/rosidl_generator_py_generate_interfaces.cmake

@@ -12,13 +12,27 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-find_package(python_cmake_module REQUIRED)
-find_package(PythonExtra REQUIRED)
 find_package(rmw REQUIRED)
 find_package(rosidl_runtime_c REQUIRED)
 find_package(rosidl_typesupport_c REQUIRED)
 find_package(rosidl_typesupport_interface REQUIRED)
 
+# By default, without the settings below, find_package(Python3) will attempt
+# to find the newest python version it can, and additionally will find the
+# most specific version.  For instance, on a system that has
+# /usr/bin/python3.10, /usr/bin/python3.11, and /usr/bin/python3, it will find
+# /usr/bin/python3.11, even if /usr/bin/python3 points to /usr/bin/python3.10.
+# The behavior we want is to prefer the "system" installed version unless the
+# user specifically tells us othewise through the Python3_EXECUTABLE hint.
+# Setting CMP0094 to NEW means that the search will stop after the first
+# python version is found.  Setting Python3_FIND_UNVERSIONED_NAMES means that
+# the search will prefer /usr/bin/python3 over /usr/bin/python3.11.  And that
+# latter functionality is only available in CMake 3.20 or later, so we need
+# at least that version.
+cmake_minimum_required(VERSION 3.20)
+cmake_policy(SET CMP0094 NEW)
+set(Python3_FIND_UNVERSIONED_NAMES FIRST)
+
 find_package(Python3 REQUIRED COMPONENTS Interpreter Development NumPy)
 
 # Get a list of typesupport implementations from valid rmw implementations.
@@ -184,7 +198,9 @@ foreach(_typesupport_impl ${_typesupport_impls})
     ${rosidl_generate_interfaces_TARGET}__rosidl_typesupport_c
   )
 
-  set_target_properties(${_target_name} PROPERTIES DEBUG_POSTFIX "${PythonExtra_POSTFIX}")
+  if(WIN32 AND CMAKE_BUILD_TYPE STREQUAL "Debug")
+    set_target_properties(${_target_name} PROPERTIES DEBUG_POSTFIX "_d")
+  endif()
   # target_compile_options(${_target_name} PRIVATE ${_extension_compile_flags})
   # TODO(sloretz) use target_compile_options when python extension passes -Wpedantic
   set_target_properties(${_target_name} PROPERTIES COMPILE_OPTIONS "${_extension_compile_flags}")

rosidl_generator_py/package.xml

@@ -23,7 +23,6 @@
 
   <buildtool_export_depend>ament_cmake</buildtool_export_depend>
   <buildtool_export_depend>ament_index_python</buildtool_export_depend>
-  <buildtool_export_depend>python_cmake_module</buildtool_export_depend>
   <buildtool_export_depend>rosidl_generator_c</buildtool_export_depend>
   <buildtool_export_depend>rosidl_pycommon</buildtool_export_depend>
   <buildtool_export_depend>rosidl_typesupport_c</buildtool_export_depend>
@@ -53,7 +52,6 @@
   <test_depend>ament_lint_common</test_depend>
   <test_depend>python3-numpy</test_depend>
   <test_depend>python3-pytest</test_depend>
-  <test_depend>python_cmake_module</test_depend>
   <test_depend>rmw</test_depend>
   <test_depend>rosidl_cmake</test_depend>