Fix argument links not working for target init_args in an optional li…

…st (#434)

CHANGELOG.rst

@@ -12,6 +12,15 @@ The semantic versioning only considers the public API as described in
 paths are considered internals and can change in minor and patch releases.
 
 
+v4.27.3 (2024-01-??)
+--------------------
+
+Fixed
+^^^^^
+- Argument links not working for target ``init_args`` in an optional list (`#433
+  <https://github.com/omni-us/jsonargparse/issues/433>`__).
+
+
 v4.27.2 (2024-01-18)
 --------------------
 

jsonargparse/_typehints.py

@@ -267,7 +267,8 @@ def is_subclass_typehint(typehint, all_subtypes=True, also_lists=False):
         if typehint_origin == Union or (also_lists and typehint_origin in sequence_origin_types):
             subtypes = [a for a in typehint.__args__ if a != NoneType]
             test = all if all_subtypes else any
-            return test(ActionTypeHint.is_subclass_typehint(s) for s in subtypes)
+            k = {"also_lists": also_lists}
+            return test(ActionTypeHint.is_subclass_typehint(s, **k) for s in subtypes)
         return (
             inspect.isclass(typehint)
             and typehint not in leaf_or_root_types

jsonargparse_tests/test_link_arguments.py

@@ -281,6 +281,28 @@ def test_on_parse_subclass_target_in_union_list(parser):
     assert all(x.init_args == Namespace(save_dir="logs") for x in cfg.trainer.logger)
 
 
+class TrainerLoggerOptionalList:
+    def __init__(
+        self,
+        save_dir: Optional[str] = None,
+        logger: Optional[List[Logger]] = None,
+    ):
+        pass
+
+
+def test_on_parse_subclass_target_in_optional_list(parser):
+    parser.add_class_arguments(TrainerLoggerOptionalList, "trainer")
+    parser.link_arguments("trainer.save_dir", "trainer.logger.init_args.save_dir")
+    cfg = parser.parse_args([])
+    assert cfg.trainer == Namespace(logger=None, save_dir=None)
+    cfg = parser.parse_args(["--trainer.save_dir=logs", "--trainer.logger+=Logger"])
+    assert cfg.trainer.save_dir == "logs"
+    assert cfg.trainer.logger[0].init_args == Namespace(save_dir="logs")
+    cfg = parser.parse_args(["--trainer.save_dir=logs", "--trainer.logger=[Logger, Logger]"])
+    assert len(cfg.trainer.logger) == 2
+    assert all(x.init_args == Namespace(save_dir="logs") for x in cfg.trainer.logger)
+
+
 class ClassF:
     def __init__(
         self,