Add colour previews to the documentation

docs/extensions/colour_preview.py

@@ -0,0 +1,51 @@
+from __future__ import annotations
+from typing import Dict, Any
+
+from sphinx.util.docutils import SphinxDirective
+from docutils.parsers.rst import directives
+from docutils import nodes
+
+import sphinx
+from sphinx.application import Sphinx
+
+
+class colour_input(nodes.General, nodes.Element):
+    pass
+
+
+def visit_colour_node(self, node):
+    self.body.append(
+        self.starttag(
+            node,
+            'input',
+            empty=True,
+            type='color',
+            value=node.rawsource,
+            disabled='',
+            CLASS=node.attributes.get('class', ''),
+        )
+    )
+
+
+def depart_colour_node(self, node):
+    pass
+
+
+class ColourDirective(SphinxDirective):
+    required_arguments = 1
+    has_content = False
+
+    option_spec = {
+        'class': directives.class_option,
+    }
+
+    def run(self):
+        node = colour_input(self.arguments[0], **self.options)
+        self.state.nested_parse(self.content, self.content_offset, node)
+        return [node]
+
+
+def setup(app: Sphinx) -> Dict[str, Any]:
+    app.add_node(colour_input, html=(visit_colour_node, depart_colour_node))
+    app.add_directive('colour', ColourDirective)
+    return {'version': sphinx.__display_version__, 'parallel_read_safe': True}