1 files changed, 82 insertions, 0 deletions
diff --git a/sphinx/extension.py b/sphinx/extension.py
new file mode 100644
index 0000000..78ef968
--- /dev/null
+++ b/sphinx/extension.py
@@ -0,0 +1,82 @@
+"""Utilities for Sphinx extensions."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+from packaging.version import InvalidVersion, Version
+
+from sphinx.errors import VersionRequirementError
+from sphinx.locale import __
+from sphinx.util import logging
+
+if TYPE_CHECKING:
+    from sphinx.application import Sphinx
+    from sphinx.config import Config
+
+logger = logging.getLogger(__name__)
+
+
+class Extension:
+    def __init__(self, name: str, module: Any, **kwargs: Any) -> None:
+        self.name = name
+        self.module = module
+        self.metadata = kwargs
+        self.version = kwargs.pop('version', 'unknown version')
+
+        # The extension supports parallel read or not.  The default value
+        # is ``None``.  It means the extension does not tell the status.
+        # It will be warned on parallel reading.
+        self.parallel_read_safe = kwargs.pop('parallel_read_safe', None)
+
+        # The extension supports parallel write or not.  The default value
+        # is ``True``.  Sphinx writes parallelly documents even if
+        # the extension does not tell its status.
+        self.parallel_write_safe = kwargs.pop('parallel_write_safe', True)
+
+
+def verify_needs_extensions(app: Sphinx, config: Config) -> None:
+    """Check that extensions mentioned in :confval:`needs_extensions` satisfy the version
+    requirement, and warn if an extension is not loaded.
+
+    Warns if an extension in :confval:`needs_extension` is not loaded.
+
+    :raises VersionRequirementError: if the version of an extension in
+    :confval:`needs_extension` is unknown or older than the required version.
+    """
+    if config.needs_extensions is None:
+        return
+
+    for extname, reqversion in config.needs_extensions.items():
+        extension = app.extensions.get(extname)
+        if extension is None:
+            logger.warning(__('The %s extension is required by needs_extensions settings, '
+                              'but it is not loaded.'), extname)
+            continue
+
+        fulfilled = True
+        if extension.version == 'unknown version':
+            fulfilled = False
+        else:
+            try:
+                if Version(reqversion) > Version(extension.version):
+                    fulfilled = False
+            except InvalidVersion:
+                if reqversion > extension.version:
+                    fulfilled = False
+
+        if not fulfilled:
+            raise VersionRequirementError(__('This project needs the extension %s at least in '
+                                             'version %s and therefore cannot be built with '
+                                             'the loaded version (%s).') %
+                                          (extname, reqversion, extension.version))
+
+
+def setup(app: Sphinx) -> dict[str, Any]:
+    app.connect('config-inited', verify_needs_extensions, priority=800)
+
+    return {
+        'version': 'builtin',
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
+    }