qapi: expose all schema features to code

This replaces use of the constants from the QapiSpecialFeatures
enum, with constants from the auto-generate QapiFeatures enum
in qapi-features.h

The 'deprecated' and 'unstable' features still have a little bit of
special handling, being force defined to be the 1st + 2nd features
in the enum, regardless of whether they're used in the schema. This
retains compatibility with common code that references the features
via the QapiSpecialFeatures constants.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250205123550.2754387-5-berrange@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Imports tidied up with isort]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/features.py

@@ -0,0 +1,48 @@
+"""
+QAPI features generator
+
+Copyright 2024 Red Hat
+
+This work is licensed under the terms of the GNU GPL, version 2.
+# See the COPYING file in the top-level directory.
+"""
+
+from typing import ValuesView
+
+from .common import c_enum_const, c_name
+from .gen import QAPISchemaMonolithicCVisitor
+from .schema import QAPISchema, QAPISchemaFeature
+
+
+class QAPISchemaGenFeatureVisitor(QAPISchemaMonolithicCVisitor):
+
+    def __init__(self, prefix: str):
+        super().__init__(
+            prefix, 'qapi-features',
+            ' * Schema-defined QAPI features',
+            __doc__)
+
+        self.features: ValuesView[QAPISchemaFeature]
+
+    def visit_begin(self, schema: QAPISchema) -> None:
+        self.features = schema.features()
+        self._genh.add("#include \"qapi/util.h\"\n\n")
+
+    def visit_end(self) -> None:
+        self._genh.add("typedef enum {\n")
+        for f in self.features:
+            self._genh.add(f"    {c_enum_const('qapi_feature', f.name)}")
+            if f.name in QAPISchemaFeature.SPECIAL_NAMES:
+                self._genh.add(f" = {c_enum_const('qapi', f.name)},\n")
+            else:
+                self._genh.add(",\n")
+
+        self._genh.add("} " + c_name('QapiFeature') + ";\n")
+
+
+def gen_features(schema: QAPISchema,
+                 output_dir: str,
+                 prefix: str) -> None:
+    vis = QAPISchemaGenFeatureVisitor(prefix)
+    schema.visit(vis)
+    vis.write(output_dir)