qapi/expr.py: Check type of union and alternate 'data' member

Prior to this commit, specifying a non-object value here causes the QAPI
parser to crash in expr.py with a stack trace with (likely) an
AttributeError when we attempt to call that value's items() method.

This member needs to be an object (Dict), and not anything else. Add a
check for this with a nicer error message, and formalize that check with
new test cases that exercise that error.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210421182032.3521476-8-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/expr.py

@@ -283,6 +283,9 @@ def check_union(expr, info):
             raise QAPISemError(info, "'discriminator' requires 'base'")
         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:
@@ -298,6 +301,10 @@ def check_alternate(expr, info):
 
     if not members:
         raise QAPISemError(info, "'data' must not be empty")
+
+    if not isinstance(members, dict):
+        raise QAPISemError(info, "'data' must be an object")
+
     for (key, value) in members.items():
         source = "'data' member '%s'" % key
         check_name_lower(key, info, source)

tests/qapi-schema/alternate-data-invalid.err

@@ -0,0 +1,2 @@
+alternate-data-invalid.json: In alternate 'Alt':
+alternate-data-invalid.json:2: 'data' must be an object

tests/qapi-schema/alternate-data-invalid.json

@@ -0,0 +1,4 @@
+# Alternate type requires an object for 'data'
+{ 'alternate': 'Alt',
+  'data': ['rubbish', 'nonsense']
+}

tests/qapi-schema/meson.build

@@ -14,6 +14,7 @@ schemas = [
   'alternate-conflict-string.json',
   'alternate-conflict-bool-string.json',
   'alternate-conflict-num-string.json',
+  'alternate-data-invalid.json',
   'alternate-empty.json',
   'alternate-invalid-dict.json',
   'alternate-nested.json',
@@ -192,6 +193,7 @@ schemas = [
   'union-clash-branches.json',
   'union-empty.json',
   'union-invalid-base.json',
+  'union-invalid-data.json',
   'union-optional-branch.json',
   'union-unknown.json',
   'unknown-escape.json',

tests/qapi-schema/union-invalid-data.err

@@ -0,0 +1,2 @@
+union-invalid-data.json: In union 'TestUnion':
+union-invalid-data.json:2: 'data' must be an object

tests/qapi-schema/union-invalid-data.json

@@ -0,0 +1,6 @@
+# the union data type must be an object.
+{ 'union': 'TestUnion',
+  'base': 'int',
+  'discriminator': 'int',
+  'data': ['rubbish', 'nonsense']
+}