qapi: add 'if' to union members

Add 'if' key to union members:

{ 'union': 'TestIfUnion', 'data':
    'mem': { 'type': 'str', 'if': 'COND'} }

The generated code remains unconditional for now. Later patches
generate the conditionals.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20181213123724.4866-16-marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

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

@@ -210,7 +210,9 @@
   [ 'foo', { 'name' : 'bar', 'if': 'defined(TEST_IF_ENUM_BAR)' } ],
   'if': 'defined(TEST_IF_ENUM)' }
 
-{ 'union': 'TestIfUnion', 'data': { 'foo': 'TestStruct' },
+{ 'union': 'TestIfUnion', 'data':
+  { 'foo': 'TestStruct',
+    'union_bar': { 'type': 'str', 'if': 'defined(TEST_IF_UNION_BAR)'} },
   'if': 'defined(TEST_IF_UNION) && defined(TEST_IF_STRUCT)' }
 
 { 'command': 'TestIfUnionCmd', 'data': { 'union_cmd_arg': 'TestIfUnion' },

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

@@ -280,11 +280,15 @@ object q_obj_TestStruct-wrapper
     member data: TestStruct optional=False
 enum TestIfUnionKind
     member foo
+    member union_bar
+        if ['defined(TEST_IF_UNION_BAR)']
     if ['defined(TEST_IF_UNION) && defined(TEST_IF_STRUCT)']
 object TestIfUnion
     member type: TestIfUnionKind optional=False
     tag type
     case foo: q_obj_TestStruct-wrapper
+    case union_bar: q_obj_str-wrapper
+        if ['defined(TEST_IF_UNION_BAR)']
     if ['defined(TEST_IF_UNION) && defined(TEST_IF_STRUCT)']
 object q_obj_TestIfUnionCmd-arg
     member union_cmd_arg: TestIfUnion optional=False

tests/qapi-schema/test-qapi.py

@@ -68,6 +68,7 @@ class QAPISchemaTestVisitor(QAPISchemaVisitor):
             print('    tag %s' % variants.tag_member.name)
             for v in variants.variants:
                 print('    case %s: %s' % (v.name, v.type.name))
+                QAPISchemaTestVisitor._print_if(v.ifcond, indent=8)
 
     @staticmethod
     def _print_if(ifcond, indent=4):