Trap case where end time of exposure is before begin time

This happens with bad FITS headers. Force the time to be the begin
time instead.

python/lsst/obs/base/_instrument.py

@@ -641,12 +641,25 @@ def makeExposureRecordFromObsInfo(
     else:
         raise RuntimeError(f"Unable to determine where to put group metadata in exposure record: {supported}")
 
+    # In some bad observations, the end time is before the begin time. We
+    # can not let that be ingested as-is because it becomes an unbounded
+    # timespan that will not work correctly with calibration lookups. Instead
+    # force the end time to be the begin time.
+    datetime_end = obsInfo.datetime_end
+    if datetime_end < obsInfo.datetime_begin:
+        datetime_end = obsInfo.datetime_begin
+        _LOG.warning(
+            "Exposure %s:%s has end time before begin time. Forcing it to use the begin time.",
+            obsInfo.instrument,
+            obsInfo.observation_id,
+        )
+
     return dimension.RecordClass(
         instrument=obsInfo.instrument,
         id=obsInfo.exposure_id,
         obs_id=obsInfo.observation_id,
         datetime_begin=obsInfo.datetime_begin,
-        datetime_end=obsInfo.datetime_end,
+        datetime_end=datetime_end,
         exposure_time=obsInfo.exposure_time.to_value("s"),
         # we are not mandating that dark_time be calculable
         dark_time=obsInfo.dark_time.to_value("s") if obsInfo.dark_time is not None else None,

tests/data/ingest/sidecar_data/dataset_3.json

@@ -0,0 +1 @@
+{"telescope": "Pretend", "instrument": "DummyCam", "location": [-5464492.282102363, -2493000.626631501, 2150943.6513960036], "exposure_id": 300, "visit_id": 300, "physical_filter": "dummy_g", "datetime_begin": [2456462.0, 0.06193332175925925], "datetime_end": [2456461.0, 0.6230896990740742], "exposure_time": 30.0, "dark_time": 30.0, "boresight_airmass": 1.072389930512202, "boresight_rotation_angle": 270.0, "boresight_rotation_coord": "sky", "detector_num": 1, "detector_name": "RXX_S01", "detector_unique_name": "0_26", "detector_serial": "076", "detector_group": "0", "detector_exposure_id": 180666823, "object": "STRIPE82L", "temperature": 273.75, "pressure": 621.3000000000001, "relative_humidity": 72.5, "tracking_radec": [320.2499333333333, 1.9444444444444445e-05], "altaz_begin": [157.95888945, 68.80710558], "science_program": "o13015", "observation_type": "science", "observation_id": "DummyDataset_3", "observation_reason": "science", "exposure_group": "3", "observing_day": 20130617, "observation_counter": 3, "__CONTENT__": "translated"}

tests/data/ingest/sidecar_data/dataset_3.yaml

@@ -0,0 +1,2 @@
+value: 3
+name: "dataset_3"

tests/test_ingest.py

@@ -134,6 +134,24 @@ def testSimpleIngest(self):
         datasets = list(self.butler.registry.queryDatasets("raw_dict", collections=self.outputRun))
         self.assertEqual(len(datasets), 2)
 
+        # Now ingest dataset_3, which should generate a warning because of
+        # the end time being before the begin time.
+        files = [os.path.join(INGESTDIR, "sidecar_data", "dataset_3.yaml")]
+        with self.assertLogs("lsst.obs.base._instrument", level="WARNING") as cm:
+            self.task.run(files, run=self.outputRun)
+
+        self.assertIn("has end time before begin time", cm.output[0])
+        records = list(
+            self.butler.registry.queryDimensionRecords(
+                "exposure",
+                where="exposure = exp AND instrument = inst",
+                bind={"exp": 300, "inst": "DummyCam"},
+            )
+        )
+        record = records[0]
+        timespan = record.timespan
+        self.assertEqual(timespan.begin.isot, timespan.end.isot)
+
     def testExplicitIndex(self):
         files = [os.path.join(INGESTDIR, "indexed_data", "_index.json")]
         self.task.run(files, run=self.outputRun)