scanner: make the invalid type message a bit easier to identify

proto/scanner.py

@@ -112,8 +112,9 @@ class Argument:
 
     @signature.validator  # type: ignore
     def _validate_signature(self, attribute, value):
-        types = "iufhnos"
-        assert value in types, f"Failed to parse signature {value}"
+        assert (
+            value is not None and value in "iufhnos"
+        ), f"Failed to parse signature {value}"
 
     @classmethod
     def create(
@@ -124,7 +125,13 @@ class Argument:
         enum: Optional["Enum"] = None,
         interface: Optional["Interface"] = None,
     ) -> "Argument":
-        return cls(name, signature, summary, enum, interface=interface)
+        return cls(
+            name=name,
+            signature=signature,
+            summary=summary,
+            enum=enum,
+            interface=interface,
+        )
 
 
 @attr.s
@@ -499,6 +506,12 @@ class Protocol(xml.sax.handler.ContentHandler):
                 )
             name = attrs["name"]
             sig = attrs["type"]
+            if proto_to_type(sig) is None:
+                raise XmlError(
+                    *self.location,
+                    f"Invalid type '{sig}' for '{self.current_interface.name}.{self.current_message.name}::{name}'",
+                )
+
             summary = attrs.get("summary", "")
             interface_name = attrs.get("interface", None)
             if interface_name is not None: