Improved error messages when fail_untyped=True #137.

Author: ioangatop

CHANGELOG.rst

@@ -19,6 +19,8 @@ Added
 ^^^^^
 - ``CLI`` support for callable class instances `#238
   <https://github.com/omni-us/jsonargparse/issues/238>`__.
+- ``add_dataclass_arguments`` now supports the ``fail_untyped`` parameter `#241
+  <https://github.com/omni-us/jsonargparse/issues/241>`__.
 
 Fixed
 ^^^^^
@@ -27,8 +29,10 @@ Fixed
 
 Changed
 ^^^^^^^
-- When parsing fails now ``argparse.ArgumentError`` is raised instead of
+- When parsing fails, now ``argparse.ArgumentError`` is raised instead of
   ``ParserError``.
+- Improved error messages when ``fail_untyped=True`` `#137
+  <https://github.com/omni-us/jsonargparse/issues/137>`__.
 
 Deprecated
 ^^^^^^^^^^

jsonargparse/signatures.py

@@ -362,7 +362,12 @@ def _add_signature_parameter(
                 action.sub_add_kwargs['skip'] = subclass_skip
             added_args.append(dest)
         elif is_required and fail_untyped:
-            raise ValueError(f'Required parameter without a type for "{src}" parameter "{name}".')
+            msg = f'With fail_untyped=True, all mandatory parameters must have a supported type. Parameter "{name}" from "{src}" '
+            if isinstance(annotation, str):
+                msg += 'specifies the type as a string. Types as a string and `from __future__ import annotations` is currently not supported.'
+            else:
+                msg += 'does not specify a type.'
+            raise ValueError(msg)
 
 
     def add_dataclass_arguments(

jsonargparse_tests/test_signatures.py

@@ -955,6 +955,25 @@ def func(a1: Optional[int] = None):
         self.assertIsNone(parser.parse_args(['--a1=null']).a1)
 
 
+    def test_fail_untyped_true(self):
+        def func1(a1):
+            return a1
+
+        parser = ArgumentParser(exit_on_error=False)
+        with self.assertRaises(ValueError) as ctx:
+            parser.add_function_arguments(func1, fail_untyped=True)
+        self.assertIn('Parameter "a1" from', str(ctx.exception))
+        self.assertIn('does not specify a type', str(ctx.exception))
+
+        def func2(a2: 'int'):
+            return a2
+
+        with self.assertRaises(ValueError) as ctx:
+            parser.add_function_arguments(func2, fail_untyped=True)
+        self.assertIn('Parameter "a2" from', str(ctx.exception))
+        self.assertIn('specifies the type as a string', str(ctx.exception))
+
+
     def test_fail_untyped_false(self):
 
         def func(a1, a2=None):