qapi: New QAPISchemaBranches, QAPISchemaAlternatives

QAPISchemaVariants represents either a union type's branches, or an
alternate type's alternatives.  Much of its code is conditional on
which one it actually is.

Create QAPISchemaBranches for branches, and QAPISchemaAlternatives for
alternatives, both subtypes of QAPISchemaVariants.

Replace QAPISchemaVariants by one of them where possible.  Keep it
only where we actually deal with either of them.

QAPISchemaVariants.__init__() takes @tag_name and @tag_member, where
exactly one must be None: @tag_name for alternatives, @tag_member for
branches.  Let QAPISchemaBranches.__init__() take just @tag_name, and
QAPISchemaAlternatives.__init__() take just @tag_member.

A later patch will move the conditional code to the subtypes.

Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 24 insertions, 8 deletions

diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 5924947fc3..5cdedfc2c8 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -215,7 +215,7 @@ class QAPISchemaVisitor:
         features: List[QAPISchemaFeature],
         base: Optional[QAPISchemaObjectType],
         members: List[QAPISchemaObjectTypeMember],
-        variants: Optional[QAPISchemaVariants],
+        variants: Optional[QAPISchemaBranches],
     ) -> None:
         pass
 
@@ -226,7 +226,7 @@ class QAPISchemaVisitor:
         ifcond: QAPISchemaIfCond,
         features: List[QAPISchemaFeature],
         members: List[QAPISchemaObjectTypeMember],
-        variants: Optional[QAPISchemaVariants],
+        variants: Optional[QAPISchemaBranches],
     ) -> None:
         pass
 
@@ -236,7 +236,7 @@ class QAPISchemaVisitor:
         info: Optional[QAPISourceInfo],
         ifcond: QAPISchemaIfCond,
         features: List[QAPISchemaFeature],
-        variants: QAPISchemaVariants,
+        variants: QAPISchemaAlternatives,
     ) -> None:
         pass
 
@@ -524,7 +524,7 @@ class QAPISchemaObjectType(QAPISchemaType):
         features: Optional[List[QAPISchemaFeature]],
         base: Optional[str],
         local_members: List[QAPISchemaObjectTypeMember],
-        variants: Optional[QAPISchemaVariants],
+        variants: Optional[QAPISchemaBranches],
     ):
         # struct has local_members, optional base, and no variants
         # union has base, variants, and no local_members
@@ -651,7 +651,7 @@ class QAPISchemaAlternateType(QAPISchemaType):
         doc: Optional[QAPIDoc],
         ifcond: Optional[QAPISchemaIfCond],
         features: List[QAPISchemaFeature],
-        variants: QAPISchemaVariants,
+        variants: QAPISchemaAlternatives,
     ):
         super().__init__(name, info, doc, ifcond, features)
         assert variants.tag_member
@@ -833,6 +833,22 @@ class QAPISchemaVariants:
             v.type.check_clash(info, dict(seen))
 
 
+class QAPISchemaBranches(QAPISchemaVariants):
+    def __init__(self,
+                 info: QAPISourceInfo,
+                 variants: List[QAPISchemaVariant],
+                 tag_name: str):
+        super().__init__(tag_name, info, None, variants)
+
+
+class QAPISchemaAlternatives(QAPISchemaVariants):
+    def __init__(self,
+                 info: QAPISourceInfo,
+                 variants: List[QAPISchemaVariant],
+                 tag_member: QAPISchemaObjectTypeMember):
+        super().__init__(None, info, tag_member, variants)
+
+
 class QAPISchemaMember:
     """ Represents object members, enum members and features """
     role = 'member'
@@ -1388,8 +1404,8 @@ class QAPISchema:
         self._def_definition(
             QAPISchemaObjectType(name, info, expr.doc, ifcond, features,
                                  base, members,
-                                 QAPISchemaVariants(
-                                     tag_name, info, None, variants)))
+                                 QAPISchemaBranches(
+                                     info, variants, tag_name)))
 
     def _def_alternate_type(self, expr: QAPIExpression) -> None:
         name = expr['alternate']
@@ -1407,7 +1423,7 @@ class QAPISchema:
         self._def_definition(
             QAPISchemaAlternateType(
                 name, info, expr.doc, ifcond, features,
-                QAPISchemaVariants(None, info, tag_member, variants)))
+                QAPISchemaAlternatives(info, variants, tag_member)))
 
     def _def_command(self, expr: QAPIExpression) -> None:
         name = expr['command']