Add connection methods to resolve dimensions.

This copies the "skypix" dimension placeholder from the
TaskDatasetTypes/PipelineDatasetTypes logic for now.  I'll delete or
at least deprecate the original shortly after the new graph class to
replace them is ready.

python/lsst/pipe/base/connectionTypes.py

@@ -30,7 +30,16 @@
 from collections.abc import Callable, Iterable, Sequence
 from typing import Optional, Union
 
-from lsst.daf.butler import DataCoordinate, DatasetRef, DatasetType, DimensionUniverse, Registry, StorageClass
+from lsst.daf.butler import (
+    DataCoordinate,
+    DatasetRef,
+    DatasetType,
+    DimensionGraph,
+    DimensionUniverse,
+    Registry,
+    SkyPixDimension,
+    StorageClass,
+)
 
 
 @dataclasses.dataclass(frozen=True)
@@ -57,6 +66,7 @@ class BaseConnection:
     storageClass: str
     doc: str = ""
     multiple: bool = False
+    isCalibration: bool = False
 
     def __get__(self, inst, klass):
         """Descriptor method
@@ -113,6 +123,34 @@ def makeDatasetType(
             self.name, universe.empty, self.storageClass, parentStorageClass=parentStorageClass
         )
 
+    def resolve_dimensions(
+        self, universe: DimensionUniverse, expected: DimensionGraph | None, task_label: str
+    ) -> DimensionGraph:
+        """Resolve the dimensions of dataset type associated with this
+        connnection.
+
+        Parameters
+        ----------
+        universe : `DimensionUniverse`
+            Set of all known dimensions to be used to normalize the dimension
+            names specified in config.
+        expected : `DimensionGraph` or `None`
+            The dimensions this dataset type is expected to have, from either
+            the data repository or an output connection in the same pipeline.
+            Implementations may use this to fill in wildcards, but do not in
+            general use it to check for consistency (as this is better handled
+            by more general code elsewhere)
+        task_label : `str`
+            Task label associated with this connection.  Should be included in
+            any error messages.
+
+        Returns
+        -------
+        dimensions : `lsst.daf.butler.DimensionGraph`
+            Fully expanded and resolved dimensions.
+        """
+        return universe.empty
+
 
 @dataclasses.dataclass(frozen=True)
 class DimensionedConnection(BaseConnection):
@@ -143,7 +181,6 @@ class DimensionedConnection(BaseConnection):
     """
 
     dimensions: typing.Iterable[str] = ()
-    isCalibration: bool = False
 
     def __post_init__(self):
         if isinstance(self.dimensions, str):
@@ -179,6 +216,12 @@ def makeDatasetType(
             parentStorageClass=parentStorageClass,
         )
 
+    def resolve_dimensions(
+        self, universe: DimensionUniverse, expected: DimensionGraph | None, task_label: str
+    ) -> DimensionGraph:
+        # Docstring inherited.
+        return universe.extract(self.dimensions)
+
 
 @dataclasses.dataclass(frozen=True)
 class BaseInput(DimensionedConnection):
@@ -315,6 +358,29 @@ class PrerequisiteInput(BaseInput):
         Callable[[DatasetType, Registry, DataCoordinate, Sequence[str]], Iterable[DatasetRef]]
     ] = None
 
+    def resolve_dimensions(
+        self, universe: DimensionUniverse, expected: DimensionGraph | None, task_label: str
+    ) -> DimensionGraph:
+        # Docstring inherited.
+        if "skypix" in self.dimensions:
+            if expected is None:
+                raise LookupError(
+                    f"DatasetType '{self.name}' referenced by "
+                    f"{task_label!r} uses 'skypix' as a dimension "
+                    f"placeholder, but does not already exist in the registry.  "
+                    f"Note that reference catalog names are now used as the dataset "
+                    f"type name instead of 'ref_cat'."
+                )
+            rest1 = set(universe.extract(set(self.dimensions) - set(["skypix"])).names)
+            rest2 = set(dim.name for dim in expected.dimensions if not isinstance(dim, SkyPixDimension))
+            if rest1 != rest2:
+                raise ValueError(
+                    f"Non-skypix dimensions for dataset type {self.name} declared in "
+                    f"connections ({rest1}) are inconsistent with those in "
+                    f"registry's version of this dataset ({rest2})."
+                )
+        return universe.extract(self.dimensions)
+
 
 @dataclasses.dataclass(frozen=True)
 class Output(DimensionedConnection):