tests/qapi-schema: Cover empty union base

The new test case shows off qapi.py choking on an empty union base.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1489582656-31133-9-git-send-email-armbru@redhat.com>

tests/Makefile.include

@@ -476,6 +476,7 @@ qapi-schema += unclosed-list.json
 qapi-schema += unclosed-object.json
 qapi-schema += unclosed-string.json
 qapi-schema += unicode-str.json
+qapi-schema += union-base-empty.json
 qapi-schema += union-base-no-discriminator.json
 qapi-schema += union-branch-case.json
 qapi-schema += union-clash-branches.json

tests/qapi-schema/union-base-empty.err

@@ -0,0 +1,10 @@
+Traceback (most recent call last):
+  File "tests/qapi-schema/test-qapi.py", line 56, in <module>
+    schema = QAPISchema(sys.argv[1])
+  File "scripts/qapi.py", line 1487, in __init__
+    self.exprs = check_exprs(parser.exprs)
+  File "scripts/qapi.py", line 921, in check_exprs
+    check_union(expr, info)
+  File "scripts/qapi.py", line 738, in check_union
+    assert base_members
+AssertionError

tests/qapi-schema/union-base-empty.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/union-base-empty.json

@@ -0,0 +1,9 @@
+# Flat union with empty base and therefore without discriminator
+
+{ 'struct': 'Empty', 'data': { } }
+
+{ 'union': 'TestUnion',
+  'base': 'Empty',
+  'discriminator': 'type',
+  'data': { 'value1': 'int',
+            'value2': 'str' } }