qapi: Hide tag_name data member of variants

Clean up the only remaining external use of the tag_name field of
QAPISchemaObjectTypeVariants, by explicitly listing the generated
'type' tag for all variants in the testsuite (you can still tell
simple unions by the -wrapper types).  Then we can mark the
tag_name field as private by adding a leading underscore to prevent
any further use.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1468468228-27827-5-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

tests/qapi-schema/qapi-schema-test.out

@@ -1,19 +1,25 @@
 alternate AltIntNum
+    tag type
     case i: int
     case n: number
 alternate AltNumInt
+    tag type
     case n: number
     case i: int
 alternate AltNumStr
+    tag type
     case n: number
     case s: str
 alternate AltStrBool
+    tag type
     case s: str
     case b: bool
 alternate AltStrInt
+    tag type
     case s: str
     case i: int
 alternate AltStrNum
+    tag type
     case s: str
     case n: number
 event EVENT_A None
@@ -50,6 +56,7 @@ object UserDefA
     member boolean: bool optional=False
     member a_b: int optional=True
 alternate UserDefAlternate
+    tag type
     case udfu: UserDefFlatUnion
     case s: str
     case i: int
@@ -72,6 +79,7 @@ object UserDefFlatUnion2
     case value2: UserDefB
 object UserDefNativeListUnion
     member type: UserDefNativeListUnionKind optional=False
+    tag type
     case integer: q_obj_intList-wrapper
     case s8: q_obj_int8List-wrapper
     case s16: q_obj_int16List-wrapper
@@ -117,6 +125,7 @@ object WrapAlternate
     member alt: UserDefAlternate optional=False
 event __ORG.QEMU_X-EVENT __org.qemu_x-Struct
 alternate __org.qemu_x-Alt
+    tag type
     case __org.qemu_x-branch: str
     case b: __org.qemu_x-Base
 object __org.qemu_x-Base
@@ -130,6 +139,7 @@ object __org.qemu_x-Struct2
     member array: __org.qemu_x-Union1List optional=False
 object __org.qemu_x-Union1
     member type: __org.qemu_x-Union1Kind optional=False
+    tag type
     case __org.qemu_x-branch: q_obj_str-wrapper
 enum __org.qemu_x-Union1Kind ['__org.qemu_x-branch']
 object __org.qemu_x-Union2

tests/qapi-schema/test-qapi.py

@@ -47,8 +47,7 @@ class QAPISchemaTestVisitor(QAPISchemaVisitor):
     @staticmethod
     def _print_variants(variants):
         if variants:
-            if variants.tag_name:
-                print '    tag %s' % variants.tag_name
+            print '    tag %s' % variants.tag_member.name
             for v in variants.variants:
                 print '    case %s: %s' % (v.name, v.type.name)