qapi: Drop simple unions

Simple unions predate flat unions.  Having both complicates the QAPI
schema language and the QAPI generator.  We haven't been using simple
unions in new code for a long time, because they are less flexible and
somewhat awkward on the wire.

The previous commits eliminated simple union from the tree.  Now drop
them from the QAPI schema language entirely, and update mentions of
"flat union" to just "union".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210917143134.412106-22-armbru@redhat.com>

1 files changed, 6 insertions, 15 deletions

diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
index 91959ee79a..819ea6ad97 100644
--- a/scripts/qapi/expr.py
+++ b/scripts/qapi/expr.py
@@ -513,27 +513,18 @@ def check_union(expr: _JSONObject, info: QAPISourceInfo) -> None:
     :return: None, ``expr`` is normalized in-place as needed.
     """
     name = cast(str, expr['union'])  # Checked in check_exprs
-    base = expr.get('base')
-    discriminator = expr.get('discriminator')
+    base = expr['base']
+    discriminator = expr['discriminator']
     members = expr['data']
 
-    if discriminator is None:   # simple union
-        if base is not None:
-            raise QAPISemError(info, "'base' requires 'discriminator'")
-    else:                       # flat union
-        check_type(base, info, "'base'", allow_dict=name)
-        if not base:
-            raise QAPISemError(info, "'discriminator' requires 'base'")
-        check_name_is_str(discriminator, info, "'discriminator'")
+    check_type(base, info, "'base'", allow_dict=name)
+    check_name_is_str(discriminator, info, "'discriminator'")
 
     if not isinstance(members, dict):
         raise QAPISemError(info, "'data' must be an object")
 
     for (key, value) in members.items():
         source = "'data' member '%s'" % key
-        if discriminator is None:
-            check_name_lower(key, info, source)
-        # else: name is in discriminator enum, which gets checked
         check_keys(value, info, source, ['type'], ['if'])
         check_if(value, info, source)
         check_type(value['type'], info, source, allow_array=not base)
@@ -664,8 +655,8 @@ def check_exprs(exprs: List[_JSONObject]) -> List[_JSONObject]:
             check_enum(expr, info)
         elif meta == 'union':
             check_keys(expr, info, meta,
-                       ['union', 'data'],
-                       ['base', 'discriminator', 'if', 'features'])
+                       ['union', 'base', 'discriminator', 'data'],
+                       ['if', 'features'])
             normalize_members(expr.get('base'))
             normalize_members(expr['data'])
             check_union(expr, info)