qapi-visit: Honor prefix of discriminator enum

When we added support for a user-specified prefix for an enum
type (commit 351d36e4), we forgot to teach the qapi-visit code
to honor that prefix in the case of using a prefixed enum as
the discriminator for a flat union.  While there is still some
on-list debate on whether we want to keep prefixes, we should
at least make it work as long as it is still part of the code
base.
Reported-by: NDaniel P. Berrange <berrange@redhat.com>
Signed-off-by: NEric Blake <eblake@redhat.com>
Message-Id: <1455665965-27638-1-git-send-email-eblake@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

scripts/qapi-visit.py

@@ -293,7 +293,8 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error
     case %(case)s:
 ''',
                      case=c_enum_const(variants.tag_member.type.name,
-                                       var.name))
+                                       var.name,
+                                       variants.tag_member.type.prefix))
         if simple_union_type:
             ret += mcgen('''
         visit_type_%(c_type)s(v, "data", &(*obj)->u.%(c_name)s, &err);

tests/qapi-schema/qapi-schema-test.json

@@ -73,14 +73,17 @@
   'base': 'UserDefZero',
   'data': { 'string': 'str', 'enum1': 'EnumOne' } }
 
+{ 'struct': 'UserDefUnionBase2',
+  'base': 'UserDefZero',
+  'data': { 'string': 'str', 'enum1': 'QEnumTwo' } }
+
 # this variant of UserDefFlatUnion defaults to a union that uses fields with
 # allocated types to test corner cases in the cleanup/dealloc visitor
 { 'union': 'UserDefFlatUnion2',
-  'base': 'UserDefUnionBase',
+  'base': 'UserDefUnionBase2',
   'discriminator': 'enum1',
   'data': { 'value1' : 'UserDefC', # intentional forward reference
-            'value2' : 'UserDefB',
-            'value3' : 'UserDefA' } }
+            'value2' : 'UserDefB' } }
 
 { 'alternate': 'UserDefAlternate',
   'data': { 'uda': 'UserDefA', 's': 'str', 'i': 'int' } }

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

@@ -121,11 +121,10 @@ object UserDefFlatUnion
     case value2: UserDefB
     case value3: UserDefB
 object UserDefFlatUnion2
-    base UserDefUnionBase
+    base UserDefUnionBase2
     tag enum1
     case value1: UserDefC
     case value2: UserDefB
-    case value3: UserDefA
 object UserDefNativeListUnion
     member type: UserDefNativeListUnionKind optional=False
     case integer: :obj-intList-wrapper
@@ -167,6 +166,10 @@ object UserDefUnionBase
     base UserDefZero
     member string: str optional=False
     member enum1: EnumOne optional=False
+object UserDefUnionBase2
+    base UserDefZero
+    member string: str optional=False
+    member enum1: QEnumTwo optional=False
 object UserDefZero
     member integer: int optional=False
 event __ORG.QEMU_X-EVENT __org.qemu_x-Struct