Added config file for readthedocs (#3086)

- Created a config file for readthedocs, because this is the only way to turn on the option "fail the build in case of warnings/errors";
- Fixed production of errors from `XPythonDomain`: now it uses standard sphinx' mechanism.

.readthedocs.yaml

@@ -0,0 +1,14 @@
+# [Read the Docs] configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+version: 2
+
+sphinx:
+    builder: html
+    configuration: docs/conf.py
+    fail_on_warning: true
+
+python:
+    version: 3.6
+    install:
+        - requirements: requirements_docs.txt

docs/_ext/xpython.py

@@ -36,7 +36,6 @@
 #
 #-------------------------------------------------------------------------------
 import docutils
-import logging
 import re
 import sphinx.domains
 import sphinx.ext
@@ -45,7 +44,7 @@
 from docutils.nodes import Node, system_message
 from typing import List, Dict, Tuple
 
-logger = logging.getLogger(__name__)
+logger = sphinx.util.logging.getLogger(__name__)
 
 
 #-------------------------------------------------------------------------------
@@ -416,7 +415,7 @@ def translate_type(objtype):
         return fulltype
 
     def warn(self, msg):
-        print("\x1B[93mWarning\x1B[33m: " + msg + "\x1B[m")
+        logger.warn(msg)
 
     def error(self, msg, node=None):
         doc = None
@@ -428,7 +427,7 @@ def error(self, msg, node=None):
             msg += f" -- at {doc}:{line}"
         else:
             msg += f" -- at {self.env.docname}"
-        logger.error(f"\x1B[91mError: {msg}\x1B[m")
+        logger.error(msg)