docs/qapi-domain: add QAPI index

Use the QAPI object registry to generate a special index just for QAPI
definitions. The index can show entries both by definition type and all
together, alphabetically.

The index can be linked from anywhere in the QEMU manual by using the
reference `qapi-index`.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250311034303.75779-7-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/sphinx/qapi_domain.py

@@ -9,12 +9,20 @@
     AbstractSet,
     Any,
     Dict,
+    Iterable,
+    List,
     NamedTuple,
+    Optional,
     Tuple,
 )
 
-from sphinx.domains import Domain, ObjType
-from sphinx.locale import __
+from sphinx.domains import (
+    Domain,
+    Index,
+    IndexEntry,
+    ObjType,
+)
+from sphinx.locale import _, __
 from sphinx.util import logging
 
 
@@ -31,6 +39,62 @@ class ObjectEntry(NamedTuple):
     aliased: bool
 
 
+class QAPIIndex(Index):
+    """
+    Index subclass to provide the QAPI definition index.
+    """
+
+    # pylint: disable=too-few-public-methods
+
+    name = "index"
+    localname = _("QAPI Index")
+    shortname = _("QAPI Index")
+
+    def generate(
+        self,
+        docnames: Optional[Iterable[str]] = None,
+    ) -> Tuple[List[Tuple[str, List[IndexEntry]]], bool]:
+        assert isinstance(self.domain, QAPIDomain)
+        content: Dict[str, List[IndexEntry]] = {}
+        collapse = False
+
+        # list of all object (name, ObjectEntry) pairs, sorted by name
+        # (ignoring the module)
+        objects = sorted(
+            self.domain.objects.items(),
+            key=lambda x: x[0].split(".")[-1].lower(),
+        )
+
+        for objname, obj in objects:
+            if docnames and obj.docname not in docnames:
+                continue
+
+            # Strip the module name out:
+            objname = objname.split(".")[-1]
+
+            # Add an alphabetical entry:
+            entries = content.setdefault(objname[0].upper(), [])
+            entries.append(
+                IndexEntry(
+                    objname, 0, obj.docname, obj.node_id, obj.objtype, "", ""
+                )
+            )
+
+            # Add a categorical entry:
+            category = obj.objtype.title() + "s"
+            entries = content.setdefault(category, [])
+            entries.append(
+                IndexEntry(objname, 0, obj.docname, obj.node_id, "", "", "")
+            )
+
+        # alphabetically sort categories; type names first, ABC entries last.
+        sorted_content = sorted(
+            content.items(),
+            key=lambda x: (len(x[0]) == 1, x[0]),
+        )
+        return sorted_content, collapse
+
+
 class QAPIDomain(Domain):
     """QAPI language domain."""
 
@@ -54,7 +118,10 @@ class QAPIDomain(Domain):
         "objects": {},  # fullname -> ObjectEntry
     }
 
-    indices = []
+    # Index pages to generate; each entry is an Index class.
+    indices = [
+        QAPIIndex,
+    ]
 
     @property
     def objects(self) -> Dict[str, ObjectEntry]: