feat: A warning is now emitted when no streams are selected

singer_sdk/streams/core.py

@@ -5,6 +5,7 @@
 import abc
 import copy
 import datetime
+import enum
 import json
 import typing as t
 import warnings
@@ -67,6 +68,11 @@
 REPLICATION_LOG_BASED = "LOG_BASED"
 
 
+class StreamSyncOutcome(enum.Flag):
+    SYNCED = 0
+    SKIPPED = enum.auto()
+
+
 class Stream(metaclass=abc.ABCMeta):  # noqa: PLR0904
     """Abstract base class for tap streams.
 
@@ -1116,6 +1122,7 @@ def _sync_records(  # noqa: C901
         # Initialize metrics
         record_counter = metrics.record_counter(self.name)
         timer = metrics.sync_timer(self.name)
+        outcome = StreamSyncOutcome.SKIPPED
 
         record_index = 0
         context_element: types.Context | None
@@ -1165,6 +1172,7 @@ def _sync_records(  # noqa: C901
                         raise
 
                     if selected:
+                        outcome = StreamSyncOutcome.SYNCED
                         if write_messages:
                             self._write_record_message(record)
 
@@ -1192,6 +1200,8 @@ def _sync_records(  # noqa: C901
             # Write final state message if we haven't already
             self._write_state_message()
 
+        return StreamSyncOutcome
+
     def _sync_batches(
         self,
         batch_config: BatchConfig,

singer_sdk/tap_base.py

@@ -4,10 +4,10 @@
 
 import abc
 import contextlib
+import enum
 import pathlib
 import typing as t
 import warnings
-from enum import Enum
 
 import click
 
@@ -42,7 +42,7 @@
 STREAM_MAPS_CONFIG = "stream_maps"
 
 
-class CliTestOptionValue(Enum):
+class CliTestOptionValue(enum.Enum):
     """Values for CLI option --test."""
 
     All = "all"
@@ -463,6 +463,7 @@ def sync_all(self) -> None:
         self.write_message(StateMessage(value=self.state))
 
         stream: Stream
+        synced_count = 0
         for stream in self.streams.values():
             if not stream.selected and not stream.has_selected_descendents:
                 self.logger.info("Skipping deselected stream '%s'.", stream.name)
@@ -486,6 +487,9 @@ def sync_all(self) -> None:
         for stream in self.streams.values():
             stream.log_sync_costs()
 
+        if not synced_count:
+            self.logger.warning("No streams selected for sync")
+
     # Command Line Execution
 
     @classmethod

tests/samples/test_tap_countries.py

@@ -5,6 +5,7 @@
 import copy
 import io
 import json
+import logging
 import typing as t
 from contextlib import redirect_stdout
 
@@ -52,13 +53,19 @@ def test_countries_primary_key():
     )
 
 
-def test_with_catalog_mismatch():
+def test_with_catalog_mismatch(caplog: pytest.LogCaptureFixture):
     """Test catalog apply with no matching stream catalog entries."""
     tap = SampleTapCountries(config=None, catalog={"streams": []})
     for stream in tap.streams.values():
         # All streams should be deselected:
         assert not stream.selected
 
+    with caplog.at_level(logging.WARNING):
+        tap.sync_all()
+
+    assert len(caplog.records) == 1
+    assert caplog.records[0].message == "N"
+
 
 def test_with_catalog_entry():
     """Test catalog apply with a matching stream catalog entry for one stream."""

tests/samples/test_tap_sqlite.py

@@ -2,6 +2,7 @@
 
 import datetime
 import json
+import logging
 import typing as t
 
 import pytest
@@ -131,6 +132,17 @@ def test_sync_sqlite_to_csv(sqlite_sample_tap: SQLTap, tmp_path: Path):
     )
 
 
+def test_sync_without_catalog(
+    sqlite_sample_db_config: dict, caplog: pytest.LogCaptureFixture
+):
+    tap = SQLiteTap(config=sqlite_sample_db_config)
+    with caplog.at_level(logging.WARNING):
+        tap.sync_all()
+
+    assert len(caplog.records) == 1
+    assert caplog.records[0].message == "No streams selected for sync"
+
+
 @pytest.fixture
 @time_machine.travel(
     datetime.datetime(2022, 1, 1, tzinfo=datetime.timezone.utc),