mock launch components causing rosdoc2 to fail Python API

Signed-off-by: R. Kent James <[email protected]>

launch_ros/doc/conf.py

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+# Copyright 2024 R. Kent James
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# -- Path setup --------------------------------------------------------------
+
+import sys
+
+from sphinx.ext.autodoc.mock import mock
+
+# -- Project information -----------------------------------------------------
+
+copyright = 'The <launch_ros> Contributors. License: Apache License 2.0'  # noqa A001
+
+# -- General configuration ---------------------------------------------------
+
+master_doc = 'index'
+
+source_suffix = {
+    '.rst': 'restructuredtext',
+    '.md': 'markdown',
+    '.markdown': 'markdown',
+}
+
+# Add mocks for decorators to prevent rosdoc2 hangs
+
+with mock(['launch']):
+    import launch  # noqa F401
+    module = sys.modules['launch']
+sys.modules['launch'] = module
+
+with mock(['launch.frontend']):
+    import launch.frontend  # noqa F401
+    module = sys.modules['launch.frontend']
+    # These are dummy decorators
+    module.expose_action = lambda _: lambda _: _
+    module.expose_substitution = lambda _: lambda _: _
+sys.modules['launch.frontend'] = module
+
+with mock(['launch.some_substitutions_type']):
+    import launch.some_substitutions_type  # noqa F401
+    module = sys.modules['launch.some_substitutions_type']
+    module.SomeSubstitutionsType_types_tuple = ()
+sys.modules['launch.some_substitutions_type'] = module
+
+# We still want autodoc to mock the base 'launch' module
+sys.modules.pop('launch')

launch_ros/doc/design.md

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+Design Documentation
+====================
+
+See [the design document](https://design.ros2.org/articles/roslaunch.html) for more information on the ros2 launch system.