fix: Keep requested keys alive in the naive scheduler

src/sciline/scheduler.py

@@ -61,11 +61,12 @@ def get(
             raise CycleError from e
 
         dependents = _count_dependents(dependencies)
+        requested = set(keys)
         results: dict[Hashable, Any] = {}
         with reporter.run_computation(graph.values()):
             for t in tasks:
                 results[t] = reporter.call_provider_with_reporting(graph[t], results)
-                _consume_arguments(graph[t], dependents, results)
+                _consume_arguments(graph[t], dependents, results, requested)
 
         return tuple(results[key] for key in keys)
 
@@ -81,11 +82,19 @@ def _count_dependents(dependencies: dict[type, tuple[type, ...]]) -> Counter[typ
 
 
 def _consume_arguments(
-    provider: Provider, counts: Counter[type], results: dict[Hashable, object]
+    provider: Provider,
+    counts: Counter[type],
+    results: dict[Hashable, object],
+    requested: set[Hashable],
 ) -> None:
+    """Discard results that no remaining provider needs.
+
+    Requested keys are kept: they are returned to the caller, so their consumer
+    count reaching zero does not mean they are no longer needed.
+    """
     for arg in provider.arg_spec.keys():
         counts[arg] -= 1
-        if counts[arg] == 0:
+        if counts[arg] == 0 and arg not in requested:
             del results[arg]
 
 

tests/pipeline_test.py

@@ -879,6 +879,20 @@ def test_compute_with_NaiveScheduler() -> None:
     assert res == 1.5
 
 
+def test_compute_returns_requested_key_that_another_requested_key_depends_on(
+    scheduler: sl.scheduler.Scheduler,
+) -> None:
+    def make_int_local() -> int:
+        return 3
+
+    def int_to_float_local(x: int) -> float:
+        return 0.5 * x
+
+    pipeline = sl.Pipeline([int_to_float_local, make_int_local])
+    # int is both a requested key and an argument of the provider of float.
+    assert pipeline.compute((int, float), scheduler=scheduler) == {int: 3, float: 1.5}
+
+
 def test_bind_and_call_no_function() -> None:
     pipeline = sl.Pipeline([make_int])
     assert pipeline.bind_and_call(()) == ()