Add support for deprecating connection templates.

This intentionally just deprecates the corresponding config entry,
keeping those config fields from being written.  The expectation is
that deprecated templates may be used in also-deprecated connections
without emitting another warning, and then both can be removed
together.

python/lsst/pipe/base/config.py

@@ -146,7 +146,10 @@ def __new__(
                 docString = "Template parameter used to format corresponding field template parameter"
                 for templateName, default in connectionsClass.defaultTemplates.items():
                     configConnectionsNamespace[templateName] = TemplateField(
-                        dtype=str, doc=docString, default=default
+                        dtype=str,
+                        doc=docString,
+                        default=default,
+                        deprecated=connectionsClass.deprecatedTemplates.get(templateName),
                     )
             # add a reference to the connection class used to create this sub
             # config

python/lsst/pipe/base/connections.py

@@ -225,14 +225,20 @@ def __new__(cls, name, bases, dct, **kwargs):
             # look up any template from base classes and merge them all
             # together
             mergeDict = {}
+            mergeDeprecationsDict = {}
             for base in bases[::-1]:
                 if hasattr(base, "defaultTemplates"):
                     mergeDict.update(base.defaultTemplates)
+                if hasattr(base, "deprecatedTemplates"):
+                    mergeDeprecationsDict.update(base.deprecatedTemplates)
             if "defaultTemplates" in kwargs:
                 mergeDict.update(kwargs["defaultTemplates"])
-
+            if "deprecatedTemplates" in kwargs:
+                mergeDeprecationsDict.update(kwargs["deprecatedTemplates"])
             if len(mergeDict) > 0:
                 kwargs["defaultTemplates"] = mergeDict
+            if len(mergeDeprecationsDict) > 0:
+                kwargs["deprecatedTemplates"] = mergeDeprecationsDict
 
             # Verify that if templated strings were used, defaults were
             # supplied as an argument in the declaration of the connection
@@ -259,6 +265,7 @@ def __new__(cls, name, bases, dct, **kwargs):
                         f" (conflicts are {nameTemplateIntersection})."
                     )
             dct["defaultTemplates"] = kwargs.get("defaultTemplates", {})
+            dct["deprecatedTemplates"] = kwargs.get("deprecatedTemplates", {})
 
         # Convert all the connection containers into frozensets so they cannot
         # be modified at the class scope

tests/test_connections.py

@@ -188,10 +188,15 @@ class TestConnectionsWithBrokenDimensionsIter(pipeBase.PipelineTask, dimensions=
     def test_deprecation(self) -> None:
         """Test support for deprecating connections."""
 
-        class TestConnections(pipeBase.PipelineTaskConnections, dimensions=self.test_dims):
+        class TestConnections(
+            pipeBase.PipelineTaskConnections,
+            dimensions=self.test_dims,
+            defaultTemplates={"t1": "dataset_type_1"},
+            deprecatedTemplates={"t1": "Deprecated in v600, will be removed after v601."},
+        ):
             input1 = pipeBase.connectionTypes.Input(
                 doc="Docs for input1",
-                name="input1_dataset_type",
+                name="input1_{t1}",
                 storageClass="StructuredDataDict",
                 deprecated="Deprecated in v50000, will be removed after v50001.",
             )
@@ -205,7 +210,9 @@ class TestConfig(pipeBase.PipelineTaskConfig, pipelineConnections=TestConnection
 
         config = TestConfig()
         with self.assertWarns(FutureWarning):
-            config.connections.input1 = "some_other_dataset_type"
+            config.connections.input1 = "dataset_type_2"
+        with self.assertWarns(FutureWarning):
+            config.connections.t1 = "dataset_type_3"
 
         with self.assertWarns(FutureWarning):
             TestConnections(config=config)