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

(The intent is to modify qapidoc.py to add this option whenever it
detects that the features list attached to a definition contains the
"unstable" entry.)

RFC: Same comments as last patch.

Signed-off-by: Harmonie Snow <harmonie@gmail.com>
Signed-off-by: John Snow <jsnow@redhat.com>
---
 docs/sphinx-static/theme_overrides.css | 6 +++++-
 docs/sphinx/qapi-domain.py             | 8 ++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/docs/sphinx-static/theme_overrides.css b/docs/sphinx-static/theme_overrides.css
index 3765cab1b20..5f58f1d5246 100644
--- a/docs/sphinx-static/theme_overrides.css
+++ b/docs/sphinx-static/theme_overrides.css
@@ -221,7 +221,7 @@ div[class^="highlight"] pre {
     margin: 0.25em;
 }
 
-.qapi-deprecated {
+.qapi-deprecated,.qapi-unstable {
     background-color: #fffef5;
     border: solid #fff176 6px;
     font-weight: bold;
@@ -230,6 +230,10 @@ div[class^="highlight"] pre {
     margin: 5px;
 }
 
+.qapi-unstable::before {
+    content: '🚧 ';
+}
+
 .qapi-deprecated::before {
     content: '⚠️ ';
 }
diff --git a/docs/sphinx/qapi-domain.py b/docs/sphinx/qapi-domain.py
index b33d9927f4d..e522102ab7c 100644
--- a/docs/sphinx/qapi-domain.py
+++ b/docs/sphinx/qapi-domain.py
@@ -127,6 +127,7 @@ class QAPIObject(ObjectDescription[Signature]):
             # These are QAPI originals:
             "since": since_validator,
             "deprecated": directives.flag,
+            "unstable": directives.flag,
         }
     )
 
@@ -256,6 +257,13 @@ def _add_pip(source: str, content: str, classname: str) -> None:
                 "qapi-deprecated",
             )
 
+        if "unstable" in self.options:
+            _add_pip(
+                ":unstable:",
+                f"This {self.objtype} is unstable/experimental.",
+                "qapi-unstable",
+            )
+
         if infopips.children:
             contentnode.insert(0, infopips)
 
-- 
2.47.0