New method to get link targets

CHANGELOG.rst

@@ -27,6 +27,8 @@ Added
   (`#698 <https://github.com/omni-us/jsonargparse/pull/698>`__).
 - Option to enable validation of default values (`#711
   <https://github.com/omni-us/jsonargparse/pull/711>`__).
+- New method to get a list of link targets (`#715
+  <https://github.com/omni-us/jsonargparse/pull/715>`__).
 
 Changed
 ^^^^^^^

jsonargparse/_link_arguments.py

@@ -515,3 +515,7 @@ def link_arguments(
             ValueError: If an invalid parameter is given.
         """
         ActionLink(self, source, target, compute_fn, apply_on)
+
+    def get_link_targets(self, apply_on: str) -> List[str]:
+        """Get all keys that are targets of links."""
+        return [a.target[0] for a in get_link_actions(self, apply_on)]  # type: ignore[arg-type]

jsonargparse_tests/test_link_arguments.py

@@ -35,6 +35,7 @@ def test_on_parse_shallow_print_config(parser):
     parser.link_arguments("a", "b")
     out = get_parse_args_stdout(parser, ["--print_config"])
     assert json_or_yaml_load(out) == {"a": 0}
+    assert parser.get_link_targets("parse") == ["b"]
 
 
 def test_on_parse_subcommand_failing_compute_fn(parser, subparser, subtests):
@@ -107,6 +108,9 @@ def test_on_parse_compute_fn_subclass_spec(parser, subtests):
         assert cfg.cal1.init_args.firstweekday == 2
         assert cfg.cal2.init_args.firstweekday == 3
 
+    with subtests.test("get_link_targets"):
+        assert parser.get_link_targets("parse") == ["cal2.init_args.firstweekday"]
+
     with subtests.test("invalid init parameter"):
         parser.set_defaults(cal1=None)
         with pytest.raises(ArgumentError) as ctx:
@@ -164,6 +168,9 @@ def test_on_parse_add_class_arguments(subtests):
         dump = json_or_yaml_load(parser.dump(cfg, skip_link_targets=False))
         assert dump == {"a": {"v1": 11, "v2": 7}, "b": {"v3": 2, "v1": 7, "v2": 18}}
 
+    with subtests.test("get_link_targets"):
+        assert parser.get_link_targets("parse") == ["b.v1", "b.v2"]
+
     with subtests.test("argument error"):
         pytest.raises(ArgumentError, lambda: parser.parse_args(["--b.v1=5"]))
 
@@ -209,6 +216,9 @@ def add(v1, v2):
         dump = json_or_yaml_load(parser.dump(cfg, skip_link_targets=False))
         assert dump["s2"] == {"class_path": f"{__name__}.ClassS2", "init_args": {"v3": 4}}
 
+    with subtests.test("get_link_targets"):
+        assert parser.get_link_targets("parse") == ["s2.init_args.v3"]
+
     with subtests.test("compute_fn invalid result type"):
         s1_value["init_args"] = {"v1": "a", "v2": "b"}
         with pytest.raises(ArgumentError):
@@ -237,6 +247,7 @@ def test_on_parse_subclass_target_in_union(parser):
     cfg = parser.parse_args(["--trainer.save_dir=logs", "--trainer.logger=Logger"])
     assert cfg.trainer.save_dir == "logs"
     assert cfg.trainer.logger.init_args == Namespace(save_dir="logs")
+    assert parser.get_link_targets("parse") == ["trainer.logger.init_args.save_dir"]
 
 
 class TrainerLoggerList:
@@ -530,6 +541,7 @@ def test_on_instantiate_link_instance_attribute():
     init = parser.instantiate_classes(cfg)
     assert init.x.x1 == 6
     assert init.y.y3 == '"8"'
+    assert parser.get_link_targets("instantiate") == ["x.x1", "y.y1", "y.y3"]
 
 
 def test_on_instantiate_link_all_group_arguments():
@@ -542,6 +554,7 @@ def test_on_instantiate_link_all_group_arguments():
     assert init["x"].x2 == 7
     help_str = get_parser_help(parser)
     assert "Group 'x': All arguments are derived from links" in help_str
+    assert parser.get_link_targets("instantiate") == ["x.x1", "y.y1", "x.x2"]
 
 
 class FailingComputeFn1:
@@ -600,6 +613,7 @@ def test_on_parse_and_instantiate_link_entire_instance(parser):
     assert isinstance(init.n, Namespace)
     assert isinstance(init.c, Calendar)
     assert init.c is init.n.calendar
+    assert parser.get_link_targets("instantiate") == ["n.calendar"]
 
 
 class ClassM:
@@ -645,6 +659,7 @@ def test_on_instantiate_link_object_in_attribute(parser):
     init = parser.instantiate_classes(cfg)
     assert init.p.calendar is init.q.calendar
     assert init.q.calendar.firstweekday == 2
+    assert parser.get_link_targets("instantiate") == ["q.calendar"]
 
 
 def test_on_parse_link_entire_subclass(parser):
@@ -656,6 +671,7 @@ def test_on_parse_link_entire_subclass(parser):
     cfg = parser.parse_args([f"--n.calendar={json.dumps(cal)}", "--q.q2=7"])
     assert cfg.n.calendar == cfg.q.calendar
     assert cfg.q.q2 == 7
+    assert parser.get_link_targets("parse") == ["q.calendar"]
 
 
 class ClassV:
@@ -789,6 +805,7 @@ def test_on_instantiate_within_deep_subclass(parser, caplog):
     assert isinstance(init.model.decoder, WithinDeepTarget)
     assert init.model.decoder.input_channels == 16
     assert "Applied link 'encoder.output_channels --> decoder.init_args.input_channels'" in caplog.text
+    assert parser.get_link_targets("instantiate") == ["model.init_args.decoder.init_args.input_channels"]
 
 
 class WithinDeeperSystem:
@@ -824,6 +841,9 @@ def test_on_instantiate_within_deeper_subclass(parser, caplog):
     assert isinstance(init.system.model.decoder, WithinDeepTarget)
     assert init.system.model.decoder.input_channels == 16
     assert "Applied link 'encoder.output_channels --> decoder.init_args.input_channels'" in caplog.text
+    assert parser.get_link_targets("instantiate") == [
+        "system.init_args.model.init_args.decoder.init_args.input_channels"
+    ]
 
 
 class SourceA: