qapi: Forbid base without discriminator in unions

None of the existing QMP or QGA interfaces uses a union with a
base type but no discriminator; it is easier to avoid this in the
generator to save room for other future extensions more likely to
be useful.  An earlier commit added a union-base-no-discriminator
test to ensure that we eventually give a decent error message;
likewise, removing UserDefUnion outright is okay, because we moved
all the tests we wish to keep into the tests of the simple union
UserDefNativeListUnion in the previous commit.  Now is the time to
actually forbid simple union with base, and remove the last
vestiges from the testsuite.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 5 insertions, 6 deletions

diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 41596bb95b..dbf0101cba 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -310,16 +310,15 @@ def generate_visit_union(expr):
         ret = ""
         disc_type = enum_define['enum_name']
     else:
-        # There will always be a discriminator in the C switch code, by default it
-        # is an enum type generated silently as "'%sKind' % (name)"
+        # There will always be a discriminator in the C switch code, by default
+        # it is an enum type generated silently as "'%sKind' % (name)"
         ret = generate_visit_enum('%sKind' % name, members.keys())
         disc_type = '%sKind' % (name)
 
     if base:
-        base_fields = find_struct(base)['data']
-        if discriminator:
-            base_fields = base_fields.copy()
-            del base_fields[discriminator]
+        assert discriminator
+        base_fields = find_struct(base)['data'].copy()
+        del base_fields[discriminator]
         ret += generate_visit_struct_fields(name, "", "", base_fields)
 
     if discriminator: