Store DimensionConfig in the DimensionUniverse

This makes it easier to send a server universe to a client without
needing to re-read from the database. Memory impact is minimal since
DimensionUniverse is already cached by version number.

python/lsst/daf/butler/core/dimensions/_config.py

@@ -256,7 +256,7 @@ def makeBuilder(self) -> DimensionConstructionBuilder:
             configuration.  The `~DimensionConstructionBuilder.finish` method
             will not have been called.
         """
-        builder = DimensionConstructionBuilder(self["version"], self["skypix", "common"])
+        builder = DimensionConstructionBuilder(self["version"], self["skypix", "common"], self)
         builder.update(self._extractSkyPixVisitors())
         builder.update(self._extractElementVisitors())
         builder.update(self._extractTopologyVisitors())

python/lsst/daf/butler/core/dimensions/_universe.py

@@ -131,6 +131,7 @@ def __new__(
         self._elements = builder.elements
         self._topology = builder.topology
         self._packers = builder.packers
+        self.dimensionConfig = builder.config
         commonSkyPix = self._dimensions[builder.commonSkyPixName]
         assert isinstance(commonSkyPix, SkyPixDimension)
         self.commonSkyPix = commonSkyPix
@@ -448,6 +449,9 @@ def __deepcopy__(self, memo: dict) -> DimensionUniverse:
     dimensions in the `Registry` database (`SkyPixDimension`).
     """
 
+    dimensionConfig: DimensionConfig
+    """The configuration used to create this Universe (`DimensionConfig`)."""
+
     _cache: Dict[FrozenSet[str], DimensionGraph]
 
     _dimensions: NamedValueAbstractSet[Dimension]

python/lsst/daf/butler/core/dimensions/construction.py

@@ -35,6 +35,7 @@
 if TYPE_CHECKING:
     from ._elements import Dimension, DimensionElement
     from ._packer import DimensionPackerFactory
+    from ._config import DimensionConfig
 
 
 class DimensionConstructionVisitor(ABC):
@@ -121,14 +122,16 @@ class DimensionConstructionBuilder:
     def __init__(
         self,
         version: int,
-        commonSkyPixName: str, *,
+        commonSkyPixName: str,
+        config: DimensionConfig, *,
         visitors: Iterable[DimensionConstructionVisitor] = ()
     ) -> None:
         self.dimensions = NamedValueSet()
         self.elements = NamedValueSet()
         self.topology = {space: NamedValueSet() for space in TopologicalSpace.__members__.values()}
         self.packers = {}
         self.version = version
+        self.config = config
         self.commonSkyPixName = commonSkyPixName
         self._todo: Dict[str, DimensionConstructionVisitor] = {v.name: v for v in visitors}
 

tests/test_dimensions.py

@@ -33,6 +33,7 @@
     DataCoordinateSequence,
     DataCoordinateSet,
     Dimension,
+    DimensionConfig,
     DimensionGraph,
     DimensionUniverse,
     NamedKeyDict,
@@ -117,6 +118,10 @@ def checkGraphInvariants(self, graph):
                     self.assertTrue(any(element in s.implied for s in seen))
         self.assertCountEqual(seen, graph.elements)
 
+    def testConfigPresent(self):
+        config = self.universe.dimensionConfig
+        self.assertIsInstance(config, DimensionConfig)
+
     def testConfigRead(self):
         self.assertEqual(self.universe.getStaticDimensions().names,
                          {"instrument", "visit", "visit_system", "exposure", "detector",