Add error check for filtering out all of the metrics in a workflow

This isn't a valid use case so just raise for it.

langkit/core/workflow.py

@@ -206,6 +206,11 @@ def run(self, data: Union[pd.DataFrame, Row, Dict[str, str]], options: Optional[
         if options and options.metric_filter and options.metric_filter.by_required_inputs:
             by_required_inputs_set = frozenset([frozenset(x) for x in options.metric_filter.by_required_inputs])
             metrics_to_run = [metric for metric in self.metrics_config.metrics if frozenset(metric.input_names) in by_required_inputs_set]
+            if not metrics_to_run:
+                raise ValueError(
+                    f"No metrics to run. Filters {options.metric_filter.by_required_inputs} did "
+                    f"not match any metrics {self.get_metric_names()}"
+                )
         else:
             metrics_to_run = self.metrics_config.metrics
 

tests/langkit/metrics/test_workflow.py

@@ -1,5 +1,7 @@
 from typing import List
 
+import pytest
+
 from langkit.core.workflow import MetricFilterOptions, RunOptions, Workflow
 from langkit.metrics.library import lib
 from langkit.validators.library import lib as validator_lib
@@ -129,6 +131,14 @@ def test_metric_filter_both_prompt_and_response():
     ]
 
 
+def test_metric_filter_no_metrics_left():
+    wf = Workflow(metrics=[lib.presets.recommended(), lib.response.similarity.prompt()])
+    options = RunOptions(metric_filter=MetricFilterOptions(by_required_inputs=[["doesnt exist"]]))
+
+    with pytest.raises(ValueError):
+        wf.run({"prompt": "hi", "response": "hello"}, options)
+
+
 def test_metric_filter_include_everything():
     wf = Workflow(metrics=[lib.presets.recommended(), lib.response.similarity.prompt()])
     options = RunOptions(metric_filter=MetricFilterOptions(by_required_inputs=[["prompt", "response"], ["prompt"], ["response"]]))