[tune] strict metric checking (#10972)

python/ray/tune/suggest/search.py

@@ -17,6 +17,12 @@ class SearchAlgorithm:
     """
     _finished = False
 
+    _metric = None
+
+    @property
+    def metric(self):
+        return self._metric
+
     def set_search_properties(self, metric: Optional[str], mode: Optional[str],
                               config: Dict) -> bool:
         """Pass search properties to search algorithm.
@@ -33,6 +39,10 @@ class SearchAlgorithm:
             mode (str): One of ["min", "max"]. Direction to optimize.
             config (dict): Tune config dict.
         """
+        if self._metric and metric:
+            return False
+        if metric:
+            self._metric = metric
         return True
 
     @property

python/ray/tune/suggest/search_generator.py

@@ -70,6 +70,10 @@ class SearchGenerator(SearchAlgorithm):
         self._total_samples = 0  # int: total samples to evaluate.
         self._finished = False
 
+    @property
+    def metric(self):
+        return self.searcher.metric
+
     def set_search_properties(self, metric: Optional[str], mode: Optional[str],
                               config: Dict) -> bool:
         return self.searcher.set_search_properties(metric, mode, config)