docs/qapi-domain: add return-nodesc

This form is used to annotate a return type without an accompanying
description, for when there is no "Returns:" information in the source
doc, but we have a return type we want to generate a cross-reference to.

The syntax is:

:return-nodesc: TypeName

It's primarily necessary because Sphinx always expects both a type and a
description for the prior form and will format it accordingly. To have a
reasonable rendering when the body is missing, we need to use a
different info field list entirely.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250711051045.51110-2-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
[Long line wrapped]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/devel/qapi-domain.rst

@@ -242,6 +242,37 @@ Example::
              }
 
 
+``:return-nodesc:``
+-------------------
+
+Document the return type of a QAPI command, without an accompanying
+description.
+
+:availability: This field list is only available in the body of the
+               Command directive.
+:syntax: ``:return-nodesc: type``
+:type: `sphinx.util.docfields.Field
+       <https://pydoc.dev/sphinx/latest/sphinx.util.docfields.Field.html?private=1>`_
+
+
+Example::
+
+   .. qapi:command:: query-replay
+      :since: 5.2
+
+      Retrieve the record/replay information.  It includes current
+      instruction count which may be used for ``replay-break`` and
+      ``replay-seek`` commands.
+
+      :return-nodesc: ReplayInfo
+
+      .. qmp-example::
+
+          -> { "execute": "query-replay" }
+          <- { "return": {
+                 "mode": "play", "filename": "log.rr", "icount": 220414 }
+             }
+
 ``:value:``
 -----------
 

docs/sphinx/qapi_domain.py

@@ -532,6 +532,14 @@ class QAPICommand(QAPIObject):
                 names=("return",),
                 can_collapse=True,
             ),
+            # :return-nodesc: TypeName
+            CompatField(
+                "returnvalue",
+                label=_("Return"),
+                names=("return-nodesc",),
+                bodyrolename="type",
+                has_arg=False,
+            ),
         ]
     )