sphinx: add qmp_lexer

Sphinx, through Pygments, does not like annotated json examples very
much. In some versions of Sphinx (1.7), it will render the non-json
portions of code blocks in red, but in newer versions (2.0) it will
throw an exception and not highlight the block at all. Though we can
suppress this warning, it doesn't bring back highlighting on non-strict
json blocks.

We can alleviate this by creating a custom lexer for QMP examples that
allows us to properly highlight these examples in a robust way, keeping
our directionality and elision notations.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reported-by: Aarushi Mehta <mehta.aaru20@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20190603214653.29369-3-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

docs/conf.py

@@ -41,7 +41,7 @@
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use an absolute path starting from qemu_docdir.
 #
-# sys.path.insert(0, os.path.join(qemu_docdir, "my_subdir"))
+sys.path.insert(0, os.path.join(qemu_docdir, "sphinx"))
 
 
 # -- General configuration ------------------------------------------------
@@ -54,7 +54,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = []
+extensions = ['qmp_lexer']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']

docs/sphinx/qmp_lexer.py

@@ -0,0 +1,43 @@
+# QEMU Monitor Protocol Lexer Extension
+#
+# Copyright (C) 2019, Red Hat Inc.
+#
+# Authors:
+#  Eduardo Habkost <ehabkost@redhat.com>
+#  John Snow <jsnow@redhat.com>
+#
+# This work is licensed under the terms of the GNU GPLv2 or later.
+# See the COPYING file in the top-level directory.
+"""qmp_lexer is a Sphinx extension that provides a QMP lexer for code blocks."""
+
+from pygments.lexer import RegexLexer, DelegatingLexer
+from pygments.lexers.data import JsonLexer
+from pygments import token
+from sphinx import errors
+
+class QMPExampleMarkersLexer(RegexLexer):
+    """
+    QMPExampleMarkersLexer lexes QMP example annotations.
+    This lexer adds support for directionality flow and elision indicators.
+    """
+    tokens = {
+        'root': [
+            (r'-> ', token.Generic.Prompt),
+            (r'<- ', token.Generic.Prompt),
+            (r' ?\.{3} ?', token.Generic.Prompt),
+        ]
+    }
+
+class QMPExampleLexer(DelegatingLexer):
+    """QMPExampleLexer lexes annotated QMP examples."""
+    def __init__(self, **options):
+        super(QMPExampleLexer, self).__init__(JsonLexer, QMPExampleMarkersLexer,
+                                              token.Error, **options)
+
+def setup(sphinx):
+    """For use by the Sphinx extensions API."""
+    try:
+        sphinx.require_sphinx('2.1')
+        sphinx.add_lexer('QMP', QMPExampleLexer)
+    except errors.VersionRequirementError:
+        sphinx.add_lexer('QMP', QMPExampleLexer())