Coalesce data ID query explanation into a single log.

Logging a single statement as multiple logs causes problems with Loki,
because each line may be rearranged or independently filtered. Logging
a single multiline message fixes this problem, without changing
behavior for console users.

Constructing the multiline message makes it impossible to defer string
evaluation, but for an error-level log this is unlikely to come up
in practice.

doc/changes/DM-45722.bugfix.md

@@ -0,0 +1 @@
+Explanatory logs for "initial data ID query returned no rows" now appear as a single log message instead of one entry per line. This improves display in log aggregators, but there is no change to console behavior.

python/lsst/pipe/base/all_dimensions_quantum_graph_builder.py

@@ -36,6 +36,7 @@
 import dataclasses
 from collections.abc import Iterator, Mapping
 from contextlib import contextmanager
+from io import StringIO
 from typing import TYPE_CHECKING, Any, final
 
 from lsst.daf.butler.registry import MissingDatasetTypeError
@@ -507,31 +508,39 @@ def from_builder(
                 yield result
 
     def log_failure(self, log: LsstLogAdapter) -> None:
-        """Emit a series of ERROR-level log message that attempts to explain
+        """Emit an ERROR-level log message that attempts to explain
         why the initial data ID query returned no rows.
 
         Parameters
         ----------
         log : `logging.Logger`
             The logger to use to emit log messages.
         """
-        log.error("Initial data ID query returned no rows, so QuantumGraph will be empty.")
-        for message in self.common_data_ids.explain_no_results():
-            log.error(message)
-        log.error(
-            "To reproduce this query for debugging purposes, run "
-            "Registry.queryDataIds with these arguments:"
-        )
-        # We could just repr() the queryArgs dict to get something
-        # the user could make sense of, but it's friendlier to
-        # put these args in an easier-to-reconstruct equivalent form
-        # so they can read it more easily and copy and paste into
-        # a Python terminal.
-        log.error("  dimensions=%s,", list(self.query_args["dimensions"].names))
-        log.error("  dataId=%s,", dict(self.query_args["dataId"].required))
-        if self.query_args["where"]:
-            log.error("  where=%s,", repr(self.query_args["where"]))
-        if "datasets" in self.query_args:
-            log.error("  datasets=%s,", list(self.query_args["datasets"]))
-        if "collections" in self.query_args:
-            log.error("  collections=%s,", list(self.query_args["collections"]))
+        # A single multiline log plays better with log aggregators like Loki.
+        buffer = StringIO()
+        try:
+            buffer.write("Initial data ID query returned no rows, so QuantumGraph will be empty.\n")
+            for message in self.common_data_ids.explain_no_results():
+                buffer.write(message)
+                buffer.write("\n")
+            buffer.write(
+                "To reproduce this query for debugging purposes, run "
+                "Registry.queryDataIds with these arguments:\n"
+            )
+            # We could just repr() the queryArgs dict to get something
+            # the user could make sense of, but it's friendlier to
+            # put these args in an easier-to-reconstruct equivalent form
+            # so they can read it more easily and copy and paste into
+            # a Python terminal.
+            buffer.write(f"  dimensions={list(self.query_args['dimensions'].names)},")
+            buffer.write(f"  dataId={dict(self.query_args['dataId'].required)},")
+            if self.query_args["where"]:
+                buffer.write(f"  where={repr(self.query_args['where'])},")
+            if "datasets" in self.query_args:
+                buffer.write(f"  datasets={list(self.query_args['datasets'])},")
+            if "collections" in self.query_args:
+                buffer.write(f"  collections={list(self.query_args['collections'])},")
+        finally:
+            # If an exception was raised, write a partial.
+            log.error(buffer.getvalue())
+            buffer.close()