qapi: Fix to reject 'data': 'mumble' in struct

A struct's 'data' must be a JSON object defining the struct's members.
The QAPI code generator incorrectly accepts a JSON string instead, and
then crashes in QAPISchema._make_members() called from
._def_struct_type().

Fix to reject it: factor check_type_implicit() out of
check_type_name_or_implicit(), and switch check_struct() to use it
instead.  Also add a test case.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230316071325.492471-9-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[More detailed commit message]

1 files changed, 15 insertions, 9 deletions

diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
index 9bae500..cae0a08 100644
--- a/scripts/qapi/expr.py
+++ b/scripts/qapi/expr.py
@@ -354,14 +354,14 @@ def check_type_name_or_array(value: Optional[object],
                            source)
 
 
-def check_type_name_or_implicit(value: Optional[object],
-                                info: QAPISourceInfo, source: str,
-                                parent_name: Optional[str]) -> None:
+def check_type_implicit(value: Optional[object],
+                        info: QAPISourceInfo, source: str,
+                        parent_name: Optional[str]) -> None:
     """
     Normalize and validate an optional implicit struct type.
 
-    Accept ``None``, ``str``, or a ``dict`` defining an implicit
-    struct type.  The latter is normalized in place.
+    Accept ``None`` or a ``dict`` defining an implicit struct type.
+    The latter is normalized in place.
 
     :param value: The value to check.
     :param info: QAPI schema source file information.
@@ -377,9 +377,6 @@ def check_type_name_or_implicit(value: Optional[object],
     if value is None:
         return
 
-    if isinstance(value, str):
-        return
-
     if not isinstance(value, dict):
         raise QAPISemError(info,
                            "%s should be an object or type name" % source)
@@ -401,6 +398,15 @@ def check_type_name_or_implicit(value: Optional[object],
         check_type_name_or_array(arg['type'], info, key_source)
 
 
+def check_type_name_or_implicit(value: Optional[object],
+                                info: QAPISourceInfo, source: str,
+                                parent_name: Optional[str]) -> None:
+    if value is None or isinstance(value, str):
+        return
+
+    check_type_implicit(value, info, source, parent_name)
+
+
 def check_features(features: Optional[object],
                    info: QAPISourceInfo) -> None:
     """
@@ -486,7 +492,7 @@ def check_struct(expr: QAPIExpression) -> None:
     name = cast(str, expr['struct'])  # Checked in check_exprs
     members = expr['data']
 
-    check_type_name_or_implicit(members, expr.info, "'data'", name)
+    check_type_implicit(members, expr.info, "'data'", name)
     check_type_name(expr.get('base'), expr.info, "'base'")