Close sphinx-doc#9820: Use setuptools.Command if available

distutils was marked as deprecated since Python 3.10 (see PEP 632).
And it will be removed since Python 3.12.  To follow the deprecation,
this starts to use `setuptools.Command` if available.

sphinx/setup_command.py

@@ -6,8 +6,6 @@
 import os
 import sys
 import warnings
-from distutils.cmd import Command
-from distutils.errors import DistutilsExecError
 from io import StringIO
 from typing import Any, Dict
 
@@ -18,6 +16,13 @@
 from sphinx.util.docutils import docutils_namespace, patch_docutils
 from sphinx.util.osutil import abspath
 
+try:
+    from setuptools import Command
+    from setuptools.errors import ExecError
+except ImportError:
+    from distutils.cmd import Command
+    from distutils.errors import DistutilsExecError as ExecError
+
 
 class BuildDoc(Command):
     """
@@ -171,8 +176,7 @@ def run(self) -> None:
                                  verbosity=self.verbosity, keep_going=self.keep_going)
                     app.build(force_all=self.all_files)
                     if app.statuscode:
-                        raise DistutilsExecError(
-                            'caused by %s builder.' % app.builder.name)
+                        raise ExecError('caused by %s builder.' % app.builder.name)
             except Exception as exc:
                 handle_exception(app, self, exc, sys.stderr)
                 if not self.pdb: