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>
---
 docs/sphinx/qapi_domain.py | 76 +++++++++++++++++++++++++++++++++++---
 1 file changed, 71 insertions(+), 5 deletions(-)

diff --git a/docs/sphinx/qapi_domain.py b/docs/sphinx/qapi_domain.py
index b17fcb93f24..716a38a5f00 100644
--- a/docs/sphinx/qapi_domain.py
+++ b/docs/sphinx/qapi_domain.py
@@ -13,6 +13,7 @@
     Iterable,
     List,
     NamedTuple,
+    Optional,
     Tuple,
     cast,
 )
@@ -22,7 +23,12 @@
 
 from compat import nested_parse
 from sphinx import addnodes
-from sphinx.domains import Domain, ObjType
+from sphinx.domains import (
+    Domain,
+    Index,
+    IndexEntry,
+    ObjType,
+)
 from sphinx.locale import _, __
 from sphinx.util import logging
 from sphinx.util.docutils import SphinxDirective
@@ -53,9 +59,10 @@ class QAPIModule(SphinxDirective):
     a pass-through for the content body. Named section titles are
     allowed in the content body.
 
-    Use this directive to associate subsequent definitions with the
-    module they are defined in for purposes of search and QAPI index
-    organization.
+    Use this directive to create entries for the QAPI module in the
+    global index and the qapi index; as well as to associate subsequent
+    definitions with the module they are defined in for purposes of
+    search and QAPI index organization.
 
     :arg: The name of the module.
     :opt no-index: Don't add cross-reference targets or index entries.
@@ -134,6 +141,62 @@ def run(self) -> List[Node]:
         return ret
 
 
+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."""
 
@@ -161,7 +224,10 @@ 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]:
-- 
2.48.1