Make MetadataMetricTask flexible in its quantum size.

The same class (and any subclasses) can now be used for metadata from
any source task, provided they only need to process one metadata
object at a time.

python/lsst/verify/tasks/metadataMetricTask.py

@@ -24,6 +24,8 @@
 
 import abc
 
+import lsst.pex.config
+
 from lsst.pipe.base import Struct, connectionTypes
 from lsst.verify.tasks import MetricTask, MetricConfig, MetricConnections, \
     MetricComputationError
@@ -60,19 +62,43 @@ class SingleMetadataMetricConnections(
         multiple=False,
     )
 
+    def __init__(self, *, config=None):
+        """Customize the connections for a specific MetricTask instance.
+
+        Parameters
+        ----------
+        config : `MetadataMetricConfig`
+            A config for `MetadataMetricTask` or one of its subclasses.
+        """
+        super().__init__(config=config)
+        if config and config.metadataDimensions != self.metadata.dimensions:
+            # Hack, but only way to get a connection without fixed dimensions
+            newMetadata = connectionTypes.Input(
+                name=self.metadata.name,
+                doc=self.metadata.doc,
+                storageClass=self.metadata.storageClass,
+                dimensions=config.metadataDimensions,
+                multiple=self.metadata.multiple,
+            )
+            self.metadata = newMetadata
+            # Registry must match actual connections
+            self.allConnections['metadata'] = self.metadata
+            # Task requires that quantum dimensions match input dimensions
+            self.dimensions = config.metadataDimensions
+
 
 class MetadataMetricConfig(
         MetricConfig,
         pipelineConnections=SingleMetadataMetricConnections):
     """A base class for metadata metric task configs.
-
-    Notes
-    -----
-    `MetadataMetricTask` classes that have CCD-level granularity can use
-    this class as-is. Support for metrics of a different granularity
-    may be added later.
     """
-    pass
+    metadataDimensions = lsst.pex.config.ListField(
+        default=SingleMetadataMetricConnections.dimensions,
+        dtype=str,
+        doc="Override for the dimensions of the 'metadata' input, when "
+            "instrumenting Tasks that don't produce one metadata object "
+            "per visit.",
+    )
 
 
 class _AbstractMetadataMetricTask(MetricTask):

python/lsst/verify/tasks/testUtils.py

@@ -158,6 +158,19 @@ def testPassThroughRun(self):
                 else:
                     self.task.run([None])
 
+    def testDimensionsOverride(self):
+        config = self.task.config
+        expectedDimensions = {"instrument", "visit"}
+        config.metadataDimensions = expectedDimensions
+
+        connections = config.connections.ConnectionsClass(config=config)
+        self.assertSetEqual(set(connections.dimensions),
+                            expectedDimensions)
+        self.assertIn(connections.metadata,
+                      connections.allConnections.values())
+        self.assertSetEqual(set(connections.metadata.dimensions),
+                            expectedDimensions)
+
 
 class ApdbMetricTestCase(gen2Utils.MetricTaskTestCase, MetricTaskTestCase):
     """Unit test base class for tests of `ApdbMetricTask`.