Improve documentation (#277)

* Add Sphinx docs
* Document node.py
* Fix C extension documentation
* Document init, shutdown, and spinning
* Document Publisher and Subscription
* Document Client and Service
* Add warnings to constructors of client and service
* Document executors and callback groups
  * Use typing,TYPE_CHECKING variable for condition imports used by annotations.
* Fix mypy errors
* Add instructions for building docs to README
* Clarify doc briefs for graph discovery functions

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

README.md

@@ -1,2 +1,16 @@
 # rclpy
 ROS Client Library for the Python language.
+
+## Building documentation
+
+Documentation can be built for `rclpy` using [Sphinx](http://www.sphinx-doc.org/en/master/).
+
+#### Install dependencies
+
+    sudo apt install python3-sphinx python3-pip
+    sudo -H pip3 install sphinx_autodoc_typehints
+
+#### Build
+
+    cd rclpy/docs
+    make html

rclpy/docs/Makefile

@@ -0,0 +1,19 @@
+# Minimal makefile for Sphinx documentation
+#
+
+# You can set these variables from the command line.
+SPHINXOPTS    =
+SPHINXBUILD   = sphinx-build
+SOURCEDIR     = source
+BUILDDIR      = build
+
+# Put it first so that "make" without argument is like "make help".
+help:
+	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+.PHONY: help Makefile
+
+# Catch-all target: route all unknown targets to Sphinx using the new
+# "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
+%: Makefile
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)

rclpy/docs/make.bat

@@ -0,0 +1,35 @@
+@ECHO OFF
+
+pushd %~dp0
+
+REM Command file for Sphinx documentation
+
+if "%SPHINXBUILD%" == "" (
+	set SPHINXBUILD=sphinx-build
+)
+set SOURCEDIR=source
+set BUILDDIR=build
+
+if "%1" == "" goto help
+
+%SPHINXBUILD% >NUL 2>NUL
+if errorlevel 9009 (
+	echo.
+	echo.The 'sphinx-build' command was not found. Make sure you have Sphinx
+	echo.installed, then set the SPHINXBUILD environment variable to point
+	echo.to the full path of the 'sphinx-build' executable. Alternatively you
+	echo.may add the Sphinx directory to PATH.
+	echo.
+	echo.If you don't have Sphinx installed, grab it from
+	echo.http://sphinx-doc.org/
+	exit /b 1
+)
+
+%SPHINXBUILD% -M %1 %SOURCEDIR% %BUILDDIR% %SPHINXOPTS%
+goto end
+
+:help
+%SPHINXBUILD% -M help %SOURCEDIR% %BUILDDIR% %SPHINXOPTS%
+
+:end
+popd

rclpy/docs/source/about.rst

@@ -0,0 +1,7 @@
+About
+=====
+
+The canonical Python API for `ROS 2 <https://index.ros.org/doc/ros2>`_.
+
+*rclpy* is built on the common C-API provided by `rcl <https://github.com/ros2/rcl>`_.
+

rclpy/docs/source/api.rst

@@ -0,0 +1,22 @@
+API
+===
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents:
+
+   api/init_shutdown
+   api/node
+   api/topics
+   api/services
+   api/actions
+   api/timers
+   api/parameters
+   api/logging
+   api/context
+   api/execution_and_callbacks
+   api/utilities
+   api/qos
+
+.. TODO(jacobperron): Document remaining API
+   api/time

rclpy/docs/source/api/actions.rst

@@ -0,0 +1,11 @@
+Actions
+=======
+
+Action Client
+-------------
+
+.. automodule:: rclpy.action.client
+
+Action Server
+-------------
+.. automodule:: rclpy.action.server

rclpy/docs/source/api/context.rst

@@ -0,0 +1,4 @@
+Context
+=======
+
+.. automodule:: rclpy.context

rclpy/docs/source/api/execution_and_callbacks.rst

@@ -0,0 +1,18 @@
+Execution and Callbacks
+=======================
+
+There are two components that control the execution of callbacks: **executors** and **callback groups**.
+
+Executors are responsible for the actual execution of callbacks and should extend the :class:`.Executor` class.
+
+Callback groups are used to enforce concurrency rules for callbacks and should extend the :class:`.CallbackGroup` class.
+
+Executors
+---------
+
+.. automodule:: rclpy.executors
+
+
+Callback Groups
+---------------
+.. automodule:: rclpy.callback_groups

rclpy/docs/source/api/init_shutdown.rst

@@ -0,0 +1,4 @@
+Initialization, Shutdown, and Spinning
+======================================
+
+.. automodule:: rclpy

rclpy/docs/source/api/logging.rst

@@ -0,0 +1,4 @@
+Logging
+=======
+
+.. automodule:: rclpy.logging

rclpy/docs/source/api/node.rst

@@ -0,0 +1,4 @@
+Node
+====
+
+.. automodule:: rclpy.node

rclpy/docs/source/api/parameters.rst

@@ -0,0 +1,12 @@
+Parameters
+==========
+
+Parameter
+---------
+
+.. automodule:: rclpy.parameter
+
+Parameter Service
+-----------------
+
+.. automodule:: rclpy.parameter_service

rclpy/docs/source/api/qos.rst

@@ -0,0 +1,4 @@
+Quality of Service
+==================
+
+.. automodule:: rclpy.qos

rclpy/docs/source/api/services.rst

@@ -0,0 +1,12 @@
+Services
+========
+
+Client
+------
+
+.. automodule:: rclpy.client
+
+Service
+-------
+
+.. automodule:: rclpy.service

rclpy/docs/source/api/timers.rst

@@ -0,0 +1,4 @@
+Timer
+=====
+
+.. automodule:: rclpy.timer

rclpy/docs/source/api/topics.rst

@@ -0,0 +1,12 @@
+Topics
+======
+
+Publisher
+---------
+
+.. automodule:: rclpy.publisher
+
+Subscription
+------------
+
+.. automodule:: rclpy.subscription

rclpy/docs/source/api/utilities.rst

@@ -0,0 +1,4 @@
+Utilities
+=========
+
+.. automodule:: rclpy.utilities