Fixups from review

python/lsst/pipe/base/tests/simpleQGraph.py

@@ -199,6 +199,114 @@ def makeTask(
         return task
 
 
+class SubTaskConnections(
+    PipelineTaskConnections,
+    dimensions=("instrument", "detector"),
+    defaultTemplates={"in_tmpl": "_in", "out_tmpl": "_out"},
+):
+    """Connections for SubTask, has one input and two outputs,
+    plus one init output.
+    """
+
+    input = cT.Input(
+        name="add_dataset{in_tmpl}",
+        dimensions=["instrument", "detector"],
+        storageClass="NumpyArray",
+        doc="Input dataset type for this task",
+    )
+    output = cT.Output(
+        name="add_dataset{out_tmpl}",
+        dimensions=["instrument", "detector"],
+        storageClass="NumpyArray",
+        doc="Output dataset type for this task",
+    )
+    output2 = cT.Output(
+        name="add2_dataset{out_tmpl}",
+        dimensions=["instrument", "detector"],
+        storageClass="NumpyArray",
+        doc="Output dataset type for this task",
+    )
+    initout = cT.InitOutput(
+        name="add_init_output{out_tmpl}",
+        storageClass="NumpyArray",
+        doc="Init Output dataset type for this task",
+    )
+
+
+class SubTaskConfig(PipelineTaskConfig, pipelineConnections=SubTaskConnections):
+    """Config for SubTask."""
+
+    subtract = pexConfig.Field[int](doc="amount to subtract", default=3)
+
+
+class SubTask(PipelineTask):
+    """Trivial PipelineTask for testing, has some extras useful for specific
+    unit tests.
+    """
+
+    ConfigClass = SubTaskConfig
+    _DefaultName = "sub_task"
+
+    initout = numpy.array([999])
+    """InitOutputs for this task"""
+
+    taskFactory: SubTaskFactoryMock | None = None
+    """Factory that makes instances"""
+
+    def run(self, input: int) -> Struct:
+        if self.taskFactory:
+            # do some bookkeeping
+            if self.taskFactory.stopAt == self.taskFactory.countExec:
+                raise RuntimeError("pretend something bad happened")
+            self.taskFactory.countExec -= 1
+
+        self.config = cast(SubTaskConfig, self.config)
+        self.metadata.add("sub", self.config.subtract)
+        output = input - self.config.subtract
+        output2 = output + self.config.subtract
+        _LOG.info("input = %s, output = %s, output2 = %s", input, output, output2)
+        return Struct(output=output, output2=output2)
+
+
+class SubTaskFactoryMock(TaskFactory):
+    """Special task factory that instantiates AddTask.
+
+    It also defines some bookkeeping variables used by SubTask to report
+    progress to unit tests.
+
+    Parameters
+    ----------
+    stopAt : `int`, optional
+        Number of times to call `run` before stopping.
+    """
+
+    def __init__(self, stopAt: int = -1):
+        self.countExec = 100  # reduced by SubTask
+        self.stopAt = stopAt  # AddTask raises exception at this call to run()
+
+    def makeTask(
+        self,
+        task_node: TaskDef | TaskNode,
+        /,
+        butler: LimitedButler,
+        initInputRefs: Iterable[DatasetRef] | None,
+    ) -> PipelineTask:
+        if isinstance(task_node, TaskDef):
+            # TODO: remove support on DM-40443.
+            warnings.warn(
+                "Passing TaskDef to TaskFactory is deprecated and will not be supported after v27.",
+                FutureWarning,
+                find_outside_stacklevel("lsst.pipe.base"),
+            )
+            task_class = task_node.taskClass
+            assert task_class is not None
+        else:
+            task_class = task_node.task_class
+        task = task_class(config=task_node.config, initInputs=None, name=task_node.label)
+        task.taskFactory = self  # type: ignore
+        return task
+
+
 def registerDatasetTypes(registry: Registry, pipeline: Pipeline | Iterable[TaskDef] | PipelineGraph) -> None:
     """Register all dataset types used by tasks in a registry.
 

tests/test_pipeline.py

@@ -35,7 +35,7 @@
 import lsst.utils.tests
 from lsst.pipe.base import LabelSpecifier, Pipeline, TaskDef
 from lsst.pipe.base.pipelineIR import LabeledSubset
-from lsst.pipe.base.tests.simpleQGraph import AddTask, makeSimplePipeline
+from lsst.pipe.base.tests.simpleQGraph import AddTask, SubTask, makeSimplePipeline
 
 
 class PipelineTestCase(unittest.TestCase):
@@ -131,6 +131,48 @@ def testMergingPipelines(self):
         pipeline1.mergePipeline(pipeline2)
         self.assertEqual(pipeline1._pipelineIR.tasks.keys(), {"task0", "task1", "task2", "task3"})
 
+        # Test merging pipelines with ambiguous tasks
+        pipeline1 = makeSimplePipeline(2)
+        pipeline2 = makeSimplePipeline(2)
+        pipeline2.addTask(SubTask, "task1")
+        pipeline2.mergePipeline(pipeline1)
+
+        # Now merge in another pipeline with a config applied.
+        pipeline3 = makeSimplePipeline(2)
+        pipeline3.addTask(SubTask, "task1")
+        pipeline3.addConfigOverride("task1", "subtract", 10)
+        pipeline3.mergePipeline(pipeline2)
+        graph = pipeline3.to_graph()
+        # assert equality from the graph to trigger ambiquity resolution
+        self.assertEqual(graph.tasks["task1"].config.subtract, 10)
+
+        # Now change the order of the merging
+        pipeline1 = makeSimplePipeline(2)
+        pipeline2 = makeSimplePipeline(2)
+        pipeline2.addTask(SubTask, "task1")
+        pipeline3 = makeSimplePipeline(2)
+        pipeline3.mergePipeline(pipeline2)
+        pipeline3.mergePipeline(pipeline1)
+        graph = pipeline3.to_graph()
+        # assert equality from the graph to trigger ambiquity resolution
+        self.assertEqual(graph.tasks["task1"].config.addend, 3)
+
+        # Now do two ambiguous chains
+        pipeline1 = makeSimplePipeline(2)
+        pipeline2 = makeSimplePipeline(2)
+        pipeline2.addTask(SubTask, "task1")
+        pipeline2.addConfigOverride("task1", "subtract", 10)
+        pipeline2.mergePipeline(pipeline1)
+
+        pipeline3 = makeSimplePipeline(2)
+        pipeline4 = makeSimplePipeline(2)
+        pipeline4.addTask(SubTask, "task1")
+        pipeline4.addConfigOverride("task1", "subtract", 7)
+        pipeline4.mergePipeline(pipeline3)
+        graph = pipeline4.to_graph()
+        # assert equality from the graph to trigger ambiquity resolution
+        self.assertEqual(graph.tasks["task1"].config.subtract, 7)
+
     def testFindingSubset(self):
         pipeline = makeSimplePipeline(2)
         pipeline._pipelineIR.labeled_subsets["test1"] = LabeledSubset("test1", set(), None)