Improve exception messages when receiving unexpected ast type

dlint/namespace.py

@@ -22,7 +22,7 @@ def from_module_node(cls, module_node):
         # hole of looking at things like function and class-scope imports and
         # conditional imports in 'if' or 'try' statements
         if not isinstance(module_node, ast.Module):
-            raise TypeError("only module-level imports are supported")
+            raise TypeError('expected type ast.Module, received {}'.format(type(module_node)))
 
         imports = []
         from_imports = []

dlint/tree.py

@@ -25,7 +25,7 @@ def decorator_name(decorator):
             # E.g. @decorator(argument)
             return decorator.func.id
     else:
-        raise TypeError(type(decorator))
+        raise TypeError('expected type ast.Attribute, ast.Name, or ast.Call, received {}'.format(type(decorator)))
 
 
 def call_name(call):
@@ -36,7 +36,7 @@ def call_name(call):
         # E.g. func_call(argument)
         return call.func.id
     else:
-        raise TypeError(type(call.func))
+        raise TypeError('expected type ast.Attribute or ast.Name, received {}'.format(type(call.func)))
 
 
 def function_has_inlinecallbacks_decorator(function):

tests/test_namespace.py

@@ -9,6 +9,8 @@
 
 import unittest
 
+import pytest
+
 import dlint
 
 
@@ -101,6 +103,12 @@ def test_as_from_import_mismatch(self):
 
         assert result == expected
 
+    def test_from_module_node_unknown_type(self):
+        unknown_type = None
+
+        with pytest.raises(TypeError):
+            dlint.namespace.Namespace.from_module_node(unknown_type)
+
 
 if __name__ == "__main__":
     unittest.main()