Skip baking task when parbake task didn't find any required recipes

src/CSET/cset_workflow/app/parbake_recipes/bin/parbake.py

@@ -17,23 +17,29 @@
 
 import json
 import os
+import subprocess
 from base64 import b64decode
 from pathlib import Path
 
 from CSET.recipes import load_recipes
 
 
-def parbake_all(variables: dict, rose_datac: Path, share_dir: Path, aggregation: bool):
+def parbake_all(
+    variables: dict, rose_datac: Path, share_dir: Path, aggregation: bool
+) -> int:
     """Generate and parbake recipes from configuration."""
     # Gather all recipes into a big list.
     recipes = list(load_recipes(variables))
     # Check we have some recipes enabled.
     if not recipes:
         raise ValueError("At least one recipe should be enabled.")
     # Parbake all recipes remaining after filtering aggregation recipes.
+    recipe_count = 0
     for recipe in filter(lambda r: r.aggregation == aggregation, recipes):
         print(f"Parbaking {recipe}", flush=True)
         recipe.parbake(rose_datac, share_dir)
+        recipe_count += 1
+    return recipe_count
 
 
 def main():
@@ -44,7 +50,23 @@ def main():
     share_dir = Path(os.environ["CYLC_WORKFLOW_SHARE_DIR"])
     aggregation = bool(os.getenv("DO_CASE_AGGREGATION"))
     # Parbake recipes for cycle.
-    parbake_all(variables, rose_datac, share_dir, aggregation)
+    recipe_count = parbake_all(variables, rose_datac, share_dir, aggregation)
+
+    # If running under cylc, notify cylc of task completion.
+    cylc_workflow_id = os.getenv("CYLC_WORKFLOW_ID")
+    cylc_task_job = os.getenv("CYLC_TASK_JOB")
+    if cylc_workflow_id and cylc_task_job:
+        message_command = [
+            "cylc",
+            "message",
+            "--",
+            cylc_workflow_id,
+            cylc_task_job,
+        ]
+        if recipe_count:
+            subprocess.run(message_command + ["start baking"], check=True)
+        else:
+            subprocess.run(message_command + ["skip baking"], check=True)
 
 
 if __name__ == "__main__":  # pragma: no cover

src/CSET/cset_workflow/flow.cylc

@@ -40,23 +40,29 @@ final cycle point = {{CSET_TRIAL_END_DATE}}
             R1/{{date}} = """
             setup_complete[^] => parbake_recipes
             setup_complete[^] => FETCH_DATA:succeed-all => fetch_complete
-            fetch_complete & parbake_recipes => bake_recipes => cycle_complete
+            fetch_complete & parbake_recipes:start_baking? => bake_recipes
+            parbake_recipes:skip_baking? => ! bake_recipes
+            parbake_recipes:skip_baking? | bake_recipes => cycle_complete
             """
         {% endfor %}
     {% elif CSET_CYCLING_MODE == "trial" %}
         # Analysis from each forecast.
         {{CSET_TRIAL_CYCLE_PERIOD}} = """
         setup_complete[^] => parbake_recipes
         setup_complete[^] => FETCH_DATA:succeed-all => fetch_complete
-        fetch_complete & parbake_recipes => bake_recipes => cycle_complete
+        fetch_complete & parbake_recipes:start_baking? => bake_recipes
+        parbake_recipes:skip_baking? => ! bake_recipes
+        parbake_recipes:skip_baking? | bake_recipes => cycle_complete
         """
     {% endif %}
 
     # Only runs on the final cycle.
     R1/$ = """
     # Run aggregation recipes.
     setup_complete[^] => parbake_aggregation_recipes
-    fetch_complete & parbake_aggregation_recipes => bake_aggregation_recipes => cycle_complete
+    fetch_complete & parbake_aggregation_recipes:start_baking? => bake_aggregation_recipes
+    parbake_aggregation_recipes:skip_baking? => ! bake_aggregation_recipes
+    parbake_aggregation_recipes:skip_baking? | bake_aggregation_recipes => cycle_complete
     # Finalise website and cleanup.
     cycle_complete => finish_website => send_email
     cycle_complete => housekeeping
@@ -102,8 +108,12 @@ final cycle point = {{CSET_TRIAL_END_DATE}}
     [[PARBAKE]]
         script = rose task-run -v --app-key=parbake_recipes
         execution time limit = PT5M
+        completion = succeeded and (start_baking or skip_baking)
         [[[environment]]]
             ENCODED_ROSE_SUITE_VARIABLES = {{b64json(ROSE_SUITE_VARIABLES)}}
+        [[[outputs]]]
+            start_baking='start baking'
+            skip_baking='skip baking'
 
     [[METPLUS]]
         [[[environment]]]

tests/workflow_utils/test_parbake_recipes.py

@@ -14,6 +14,7 @@
 
 """Tests for parbake_recipe workflow utility."""
 
+import subprocess
 from pathlib import Path
 
 import pytest
@@ -25,14 +26,28 @@
 def test_main(monkeypatch):
     """Check parbake.main() invokes parbake_all correctly."""
     function_ran = False
+    recipes_parbaked = 0
+    cylc_message_ran = False
+    cylc_message = ""
 
     def mock_parbake_all(variables, rose_datac, share_dir, aggregation):
         nonlocal function_ran
+        nonlocal recipes_parbaked
         function_ran = True
         assert variables == {"variable": "value"}
         assert rose_datac == Path("/share/cycle/20000101T0000Z")
         assert share_dir == Path("/share")
         assert isinstance(aggregation, bool)
+        return recipes_parbaked
+
+    def mock_run(cmd, **kwargs):
+        nonlocal cylc_message
+        nonlocal cylc_message_ran
+        cylc_message_ran = True
+        assert cmd[0:3] == ["cylc", "message", "--"]
+        assert cmd[3] == "test-workflow"
+        assert cmd[4] == "test-job"
+        assert cmd[5] == cylc_message
 
     monkeypatch.setattr(parbake, "parbake_all", mock_parbake_all)
 
@@ -51,6 +66,25 @@ def mock_parbake_all(variables, rose_datac, share_dir, aggregation):
     parbake.main()
     assert function_ran, "Function did not run!"
 
+    # Retry with cylc environment variables set.
+    monkeypatch.setattr(subprocess, "run", mock_run)
+    monkeypatch.setenv("CYLC_WORKFLOW_ID", "test-workflow")
+    monkeypatch.setenv("CYLC_TASK_JOB", "test-job")
+
+    # No recipes parbaked.
+    function_ran = False
+    recipes_parbaked = 0
+    cylc_message = "skip baking"
+    parbake.main()
+    assert cylc_message_ran, "Cylc message function did not run!"
+
+    # Some recipes parbaked.
+    function_ran = False
+    recipes_parbaked = 3
+    cylc_message = "start baking"
+    parbake.main()
+    assert cylc_message_ran, "Cylc message function did not run!"
+
 
 def test_parbake_all_none_enabled(tmp_working_dir, monkeypatch):
     """Error when no recipes are enabled."""