[doc] html_unescape: Create html.unescape extension

This new sphinx extension runs html.unescape
(from the Python Standard Library) on source files before they are
rendered, allowing escape sequences like  ' ' for the no-break
space character.

I have also published this extension in my own name under a different
license (the same one Sphinx uses) for others to use:
https://github.com/JJRcop/sphinxcontrib-html_unescape

doc/conf.py

@@ -37,6 +37,7 @@ rst_prolog = """
 
 extensions = [
     'sphinx_rtd_theme',
+    'html_unescape',
 ]
 
 try:
@@ -64,6 +65,14 @@ exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']
 # Explicitly state master_doc instead of relying on default
 master_doc = 'index'
 
+# Documents to exclude from html_unescape
+# For example ['index', 'credits']
+html_unescape_exclude = []
+
+# If not empty, html_unescape will ignore any documents not in the list
+# For example ['install', 'usage']
+html_unescape_onlyinclude = []
+
 # -- Options for HTML output -------------------------------------------------
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for

doc/html_unescape.py

@@ -0,0 +1,58 @@
+# Copyright 2023 The Looking Glass Authors
+# https://looking-glass.io
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the Free
+# Software Foundation; either version 2 of the License, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+# more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc., 59
+# Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+
+# Call html.unescape on source files when building docs
+#
+# This converts named HTML character references: like '>' into '>',
+# and numeric references: like '🔎' into '🔎'
+#
+# See https://docs.python.org/3/library/html.html#html.unescape
+# and https://html.spec.whatwg.org/multipage/named-characters.html#named-character-references
+# for more information on available sequences
+
+from html import unescape
+
+# For type hints (PEP 484)
+from sphinx.application import Sphinx
+from sphinx.environment import BuildEnvironment
+
+
+def unescape_source(app: Sphinx, docname: str, source: list) -> None:
+    env: BuildEnvironment = app.env
+    exclude: list = env.config.html_unescape_exclude
+    onlyinclude: list = env.config.html_unescape_onlyinclude
+    docpath: str = env.doc2path(docname, base=False)
+    if docname in exclude:
+        return
+    if docpath in exclude:
+        return
+    if len(onlyinclude) and not (docname in onlyinclude or docpath in onlyinclude):
+        return
+    source[0] = unescape(source[0])
+
+
+def setup(app: Sphinx) -> dict[str, bool | str]:
+    app.add_config_value('html_unescape_exclude', [], 'env', [list])
+    app.add_config_value('html_unescape_onlyinclude', [], 'env', [list])
+    app.connect('source-read', unescape_source)
+    return {
+        'version': '1.0',
+        'env_version': '1.0',
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
+    }