docs/qapi-domain: add QAPIObject class

This patch adds another abstract class that describes "a QAPI
thingie". The main difference here is that this class will be generating
visible documentation, unlike the QAPIDescription class.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250311034303.75779-13-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/sphinx/qapi_domain.py

@@ -18,7 +18,9 @@ from typing import (
 )
 
 from docutils import nodes
+from docutils.parsers.rst import directives
 
+from compat import KeywordNode, SpaceNode
 from sphinx import addnodes
 from sphinx.addnodes import desc_signature, pending_xref
 from sphinx.directives import ObjectDescription
@@ -40,6 +42,7 @@ if TYPE_CHECKING:
     from sphinx.application import Sphinx
     from sphinx.builders import Builder
     from sphinx.environment import BuildEnvironment
+    from sphinx.util.typing import OptionSpec
 
 logger = logging.getLogger(__name__)
 
@@ -99,6 +102,8 @@ class QAPIXRefRole(XRefRole):
         return title, target
 
 
+# Alias for the return of handle_signature(), which is used in several places.
+# (In the Python domain, this is Tuple[str, str] instead.)
 Signature = str
 
 
@@ -194,6 +199,65 @@ class QAPIDescription(ObjectDescription[Signature]):
         return ""
 
 
+class QAPIObject(QAPIDescription):
+    """
+    Description of a generic QAPI object.
+
+    It's not used directly, but is instead subclassed by specific directives.
+    """
+
+    # Inherit some standard options from Sphinx's ObjectDescription
+    option_spec: OptionSpec = (  # type:ignore[misc]
+        ObjectDescription.option_spec.copy()
+    )
+    option_spec.update(
+        {
+            # Borrowed from the Python domain:
+            "module": directives.unchanged,  # Override contextual module name
+        }
+    )
+
+    def get_signature_prefix(self) -> List[nodes.Node]:
+        """Return a prefix to put before the object name in the signature."""
+        assert self.objtype
+        return [
+            KeywordNode("", self.objtype.title()),
+            SpaceNode(" "),
+        ]
+
+    def get_signature_suffix(self) -> List[nodes.Node]:
+        """Return a suffix to put after the object name in the signature."""
+        return []
+
+    def handle_signature(self, sig: str, signode: desc_signature) -> Signature:
+        """
+        Transform a QAPI definition name into RST nodes.
+
+        This method was originally intended for handling function
+        signatures. In the QAPI domain, however, we only pass the
+        definition name as the directive argument and handle everything
+        else in the content body with field lists.
+
+        As such, the only argument here is "sig", which is just the QAPI
+        definition name.
+        """
+        modname = self.options.get(
+            "module", self.env.ref_context.get("qapi:module")
+        )
+
+        signode["fullname"] = sig
+        signode["module"] = modname
+        sig_prefix = self.get_signature_prefix()
+        if sig_prefix:
+            signode += addnodes.desc_annotation(
+                str(sig_prefix), "", *sig_prefix
+            )
+        signode += addnodes.desc_name(sig, sig)
+        signode += self.get_signature_suffix()
+
+        return sig
+
+
 class QAPIModule(QAPIDescription):
     """
     Directive to mark description of a new module.