fix(docs): mock rcl_interfaces to fix empty Node API page

[mjcarroll]

Description

Fixes the empty Node API docs page reported in #1681.

rclpy.node imports rcl_interfaces.msg at module level, which transitively requires rosidl_pycommon.interface_base_classes — unavailable in the Sphinx docs build environment. The import silently fails and autodoc renders a blank page. Adding autodoc_mock_imports = ['rcl_interfaces'] to conf.py unblocks the import without affecting the build.

All other modules (publisher, client, etc.) happen to avoid this because they don't import rcl_interfaces directly.

Testing

# Clone and check out this branch
git clone https://github.com/ros2/rclpy.git && cd rclpy

# Install deps (rclpy must be importable — source your ROS install first)
source /opt/ros/rolling/setup.bash
pip install sphinx sphinx-rtd-theme

# Build docs
cd rclpy/docs
sphinx-build -b html source /tmp/rclpy-docs

# Open the Node page and confirm it has content (not just a heading)
xdg-open /tmp/rclpy-docs/api/node.html
# or: grep -c 'py class\|py method' /tmp/rclpy-docs/api/node.html

Before this fix: api/node.html contains only <h1>Node</h1> — no class or method entries.
After this fix: Node class with all ~124 methods is documented.

To reproduce the failure, revert conf.py and rebuild.

Did you use Generative AI?

Yes — Antigravity (Gemini CLI / Claude Sonnet 4.6) was used to diagnose the root cause and author the fix.

[mergify]

Tick the box to add this pull request to the merge queue (same as @mergifyio queue).

• Queue this pull request