docs/qapi-domain: add :deprecated: directive option

Although "deprecated" is a feature (and *will* appear in the features
list), add a special :deprecated: option to generate an eye-catch that
makes this information very hard to miss.

The forthcoming Transmogrifier in qapidoc.py will add this option
whenever it detects that the features list attached to a definition
contains the "deprecated" entry.

P.S., I outsourced the CSS ;)

Signed-off-by: Harmonie Snow <harmonie@gmail.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250311034303.75779-24-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/sphinx-static/theme_overrides.css

@@ -208,3 +208,28 @@ div[class^="highlight"] pre {
         color: inherit;
     }
 }
+
+/* QAPI domain theming */
+
+.qapi-infopips {
+    margin-bottom: 1em;
+}
+
+.qapi-infopip {
+    display: inline-block;
+    padding: 0em 0.5em 0em 0.5em;
+    margin: 0.25em;
+}
+
+.qapi-deprecated {
+    background-color: #fffef5;
+    border: solid #fff176 6px;
+    font-weight: bold;
+    padding: 8px;
+    border-radius: 15px;
+    margin: 5px;
+}
+
+.qapi-deprecated::before {
+    content: '⚠️ ';
+}

docs/sphinx/qapi_domain.py

@@ -217,6 +217,7 @@ class QAPIObject(QAPIDescription):
             "module": directives.unchanged,  # Override contextual module name
             # These are QAPI originals:
             "since": directives.unchanged,
+            "deprecated": directives.flag,
         }
     )
 
@@ -280,6 +281,31 @@ class QAPIObject(QAPIDescription):
 
         return sig
 
+    def _add_infopips(self, contentnode: addnodes.desc_content) -> None:
+        # Add various eye-catches and things that go below the signature
+        # bar, but precede the user-defined content.
+        infopips = nodes.container()
+        infopips.attributes["classes"].append("qapi-infopips")
+
+        def _add_pip(source: str, content: str, classname: str) -> None:
+            node = nodes.container(source)
+            node.append(nodes.Text(content))
+            node.attributes["classes"].extend(["qapi-infopip", classname])
+            infopips.append(node)
+
+        if "deprecated" in self.options:
+            _add_pip(
+                ":deprecated:",
+                f"This {self.objtype} is deprecated.",
+                "qapi-deprecated",
+            )
+
+        if infopips.children:
+            contentnode.insert(0, infopips)
+
+    def transform_content(self, content_node: addnodes.desc_content) -> None:
+        self._add_infopips(content_node)
+
 
 class QAPICommand(QAPIObject):
     """Description of a QAPI Command."""