Improve error message when no good config is found (#455)

Author: oulgen

helion/autotuner/base_search.py

@@ -386,6 +386,8 @@ def population_statistics(population: list[PopulationMember]) -> str:
     population = sorted(population, key=performance)
     if math.isinf(population[-1].perf):
         working = [x for x in population if not math.isinf(x.perf)]
+        if len(working) == 0:
+            raise exc.NoConfigFound
         return (
             f"failed={len(population) - len(working)} "
             f"min={working[0].perf:.4f} "

helion/exc.py

@@ -245,6 +245,10 @@ class NotEnoughConfigs(BaseError):
     message = "FiniteSearch requires at least two configs, but got {0}."
 
 
+class NoConfigFound(BaseError):
+    message = "No working config found from autotuning"
+
+
 class CantCombineTypesInControlFlow(BaseError):
     message = "Cannot combine types for {0!r} in control flow: {1} and {2}"