qapi: Report invalid '*' prefix like any other invalid name

The special "does not allow optional name" error is well meant, but
confusing in practice.  Drop it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190927134639.4284-12-armbru@redhat.com>

scripts/qapi/common.py

@@ -724,11 +724,8 @@ def check_name_str(name, info, source,
     global valid_name
     membername = name
 
-    if name.startswith('*'):
+    if allow_optional and name.startswith('*'):
         membername = name[1:]
-        if not allow_optional:
-            raise QAPISemError(info, "%s does not allow optional name '%s'"
-                               % (source, name))
     # Enum members can start with a digit, because the generated C
     # code always prefixes it with the enum name
     if enum_member and membername[0].isdigit():
@@ -741,6 +738,7 @@ def check_name_str(name, info, source,
     if not permit_upper and name.lower() != name:
         raise QAPISemError(
             info, "%s uses uppercase in name '%s'" % (source, name))
+    assert not membername.startswith('*')
 
 
 def add_name(name, info, meta):

tests/qapi-schema/bad-ident.err

@@ -1,2 +1,2 @@
 tests/qapi-schema/bad-ident.json: In struct '*oops':
-tests/qapi-schema/bad-ident.json:2: 'struct' does not allow optional name '*oops'
+tests/qapi-schema/bad-ident.json:2: 'struct' uses invalid name '*oops'

tests/qapi-schema/flat-union-discriminator-bad-name.err

@@ -1,2 +1,2 @@
 tests/qapi-schema/flat-union-discriminator-bad-name.json: In union 'MyUnion':
-tests/qapi-schema/flat-union-discriminator-bad-name.json:7: discriminator of flat union 'MyUnion' does not allow optional name '*switch'
+tests/qapi-schema/flat-union-discriminator-bad-name.json:7: discriminator of flat union 'MyUnion' uses invalid name '*switch'

tests/qapi-schema/flat-union-discriminator-bad-name.json

@@ -1,5 +1,5 @@
 # discriminator '*switch' isn't a member of base, 'switch' is
-# reports "does not allow optional name", which is good enough
+# reports "uses invalid name", which is good enough
 { 'enum': 'Enum', 'data': [ 'one', 'two' ] }
 { 'struct': 'Base',
   'data': { '*switch': 'Enum' } }

tests/qapi-schema/union-optional-branch.err

@@ -1,2 +1,2 @@
 tests/qapi-schema/union-optional-branch.json: In union 'Union':
-tests/qapi-schema/union-optional-branch.json:2: member of union 'Union' does not allow optional name '*a'
+tests/qapi-schema/union-optional-branch.json:2: member of union 'Union' uses invalid name '*a'