[RFC,1/3] sphinx: import sphinxcontrib.rsvgconverter sphinx plugin in-tree

diff --git a/documentation/sphinx/rsvgconverter.py b/documentation/sphinx/rsvgconverter.py
new file mode 100644
index 000000000..5ae858029
--- /dev/null
+++ b/documentation/sphinx/rsvgconverter.py
@@ -0,0 +1,96 @@ 
+# -*- coding: utf-8 -*-
+"""
+    sphinxcontrib.rsvgconverter
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    Converts SVG images to PDF using libRSVG in case the builder does not
+    support SVG images natively (e.g. LaTeX).
+
+    :copyright: Copyright 2018-2023 by Stefan Wiehler
+                <sphinx_contribute@missinglinkelectronics.com>.
+    :license: BSD, see LICENSE.txt for details.
+"""
+import subprocess
+
+from sphinx.errors import ExtensionError
+from sphinx.locale import __
+from sphinx.transforms.post_transforms.images import ImageConverter
+from sphinx.util import logging
+from errno import ENOENT, EPIPE, EINVAL
+
+if False:
+    # For type annotation
+    from typing import Any, Dict  # NOQA
+    from sphinx.application import Sphinx  # NOQA
+
+
+logger = logging.getLogger(__name__)
+
+
+class RSVGConverter(ImageConverter):
+    conversion_rules = [
+        ('image/svg+xml', 'application/pdf'),
+    ]
+
+    def is_available(self):
+        # type: () -> bool
+        """Confirms if RSVG converter is available or not."""
+        try:
+            args = [self.config.rsvg_converter_bin, '--version']
+            logger.debug('Invoking %r ...', args)
+            ret = subprocess.call(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
+            if ret == 0:
+                return True
+            else:
+                return False
+        except (OSError, IOError):
+            logger.warning(__('RSVG converter command %r cannot be run. '
+                              'Check the rsvg_converter_bin setting'),
+                           self.config.rsvg_converter_bin)
+            return False
+
+    def convert(self, _from, _to):
+        # type: (unicode, unicode) -> bool
+        """Converts the image from SVG to PDF via libRSVG."""
+        try:
+            args = ([self.config.rsvg_converter_bin] +
+                    self.config.rsvg_converter_args +
+                    ['--format=' + self.config.rsvg_converter_format,
+                     '--output=' + str(_to), str(_from)])
+            logger.debug('Invoking %r ...', args)
+            p = subprocess.Popen(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
+        except OSError as err:
+            if err.errno != ENOENT:  # No such file or directory
+                raise
+            logger.warning(__('RSVG converter command %r cannot be run. '
+                              'Check the rsvg_converter_bin setting'),
+                           self.config.rsvg_converter_bin)
+            return False
+
+        try:
+            stdout, stderr = p.communicate()
+        except (OSError, IOError) as err:
+            if err.errno not in (EPIPE, EINVAL):
+                raise
+            stdout, stderr = p.stdout.read(), p.stderr.read()
+            p.wait()
+        if p.returncode != 0:
+            raise ExtensionError(__('RSVG converter exited with error:\n'
+                                    '[stderr]\n%s\n[stdout]\n%s') %
+                                 (stderr, stdout))
+
+        return True
+
+
+def setup(app):
+    # type: (Sphinx) -> Dict[unicode, Any]
+    app.add_post_transform(RSVGConverter)
+    app.add_config_value('rsvg_converter_bin', 'rsvg-convert', 'env')
+    app.add_config_value('rsvg_converter_args', [], 'env')
+    app.add_config_value('rsvg_converter_format', 'pdf', 'env')
+
+    return {
+        'version': 'builtin',
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
+    }