CommonMark backend: replace recommonmark with MyST

recommonmark was deprectated in in May 2021

CHANGES.rst

@@ -32,6 +32,9 @@ New Features:
 
 Changed:
 
+* `MyST <https://github.com/executablebooks/MyST-Parser>`_ replaces
+  `recommonmark <https://github.com/readthedocs/recommonmark>`_ for Markdown
+  support (issues #265 and #370)
 * The Article template has been overhauled. The title page and front matter
   parts have been removed and their contents are moved to the first content
   page. This makes the Article template more useful, since it was too similar

pyproject.toml

@@ -88,8 +88,8 @@ python = "^3.7.0"
 appdirs = "^1.4.3"
 docutils = ">=0.15"
 importlib-metadata = {version = ">=0.21", python = "<3.8"}
+myst-parser = "^0.18.1"
 packaging = ">=14.0"
-recommonmark = ">=0.6.0"
 rinoh-typeface-dejavuserif = "^0.1.3"
 rinoh-typeface-texgyrecursor = "^0.1.1"
 rinoh-typeface-texgyreheros = "^0.1.1"

src/rinoh/frontend/commonmark/__init__.py

@@ -5,7 +5,7 @@
 # Use of this source code is subject to the terms of the GNU Affero General
 # Public License v3. See the LICENSE file or http://www.gnu.org/licenses/.
 
-from recommonmark.parser import CommonMarkParser
+from myst_parser.docutils_ import Parser
 
 from ..rst import DocutilsReader
 
@@ -15,4 +15,4 @@
 
 class CommonMarkReader(DocutilsReader):
     extensions = ('md', )
-    parser_class = CommonMarkParser
+    parser_class = Parser

src/rinoh/frontend/rst/nodes.py

@@ -349,9 +349,9 @@ class Literal_Block(DocutilsBodyNode):
     @property
     def language(self):
         classes = self.get('classes')
-        if classes and classes[0] == 'code':    # .. code::
-            return classes[1]
-        return None                             # literal block (double colon)
+        if len(classes) > 1 and classes[0] == 'code':    # .. code::
+            return classes[1]                            # (MyST doesn't add the
+        return None     # literal block (double colon)      language as class)
 
     def build_flowable(self):
         return rt.CodeBlock(self.text, language=self.language,