Now values are first validated before giving them to the compute_fn o…

…f arguments links applied on parse.

CHANGELOG.rst

@@ -30,6 +30,8 @@ Fixed
 - Incorrect replacement of ``**kwargs`` when ``*args`` present in parameter resolver.
 - Override of ``class_path`` not discarding ``init_args`` when loading from
   config file.
+- Invalid values given to the ``compute_fn`` of a argument link applied on parse
+  without showing an understandable error message.
 
 Changed
 ^^^^^^^

jsonargparse/link_arguments.py

@@ -5,7 +5,7 @@
 from argparse import Action, SUPPRESS
 from collections import defaultdict
 from typing import Any, Callable, List, Optional, Tuple, Type, Union
-from .actions import _ActionConfigLoad, _ActionSubCommands, ActionConfigFile, filter_default_actions, _find_parent_action
+from .actions import _ActionConfigLoad, _ActionSubCommands, ActionConfigFile, filter_default_actions, _find_action, _find_parent_action
 from .namespace import Namespace, split_key_leaf
 from .type_checking import ArgumentParser, _ArgumentGroup
 
@@ -207,6 +207,7 @@ def apply_parsing_links(parser: 'ArgumentParser', cfg: Namespace) -> None:
                 for source_key, source_action in action.source:
                     if ActionTypeHint.is_subclass_typehint(source_action[0]) and source_key not in cfg:
                         parser.logger.debug(f'Link {action.option_strings[0]} ignored since source {source_action[0]._typehint} does not have that parameter.')
+                    parser._check_value_key(source_action[0], cfg[source_action[0].dest], source_action[0].dest, None)
                     args.append(cfg[source_key])
             except KeyError:
                 continue

jsonargparse_tests/test_link_arguments.py

@@ -37,6 +37,23 @@ def a_prod(a):
         self.assertEqual(dump, {'a': {'v1': 2, 'v2': -5}})
 
 
+    def test_link_arguments_on_parse_invalid_compute_fn_arg(self):
+        parser = ArgumentParser(error_handler=None)
+        parser.add_argument('--cal1', type=Calendar, default=lazy_instance(TextCalendar))
+        parser.add_argument('--cal2', type=Calendar, default=lazy_instance(Calendar))
+        parser.link_arguments(
+            'cal1',
+            'cal2.init_args.firstweekday',
+            compute_fn=lambda c: c.init_args.firstweekday+1,
+        )
+        cfg = parser.parse_args(['--cal1.init_args.firstweekday=2'])
+        self.assertEqual(cfg.cal1.init_args.firstweekday, 2)
+        self.assertEqual(cfg.cal2.init_args.firstweekday, 3)
+        with self.assertRaises(ParserError) as cm:
+            parser.parse_args(['--cal1.class_path.init_args.firstweekday=2'])
+        self.assertIn('Parser key "cal1"', str(cm.exception))
+
+
     def test_link_arguments_on_parse_add_class_arguments(self):
         class ClassA:
             def __init__(self, v1: int = 2, v2: int = 3):