added a warning when n_trials budget is depleted but ask still return trials

docs/advanced_usage/5_ask_and_tell.md

@@ -15,6 +15,13 @@ and report the results of the trial.
     different budgets, they, obviously, can not be considered. However, all user-provided configurations will flow 
     into the intensification process.
 
+!!! warning 
+
+    In pure ask-and-tell usage, SMAC does not hard-stop `ask()` when `n_trials` is depleted. (This is true for any kind of budget exhaustion and not only `n_trials` eg. walltime, cputime. warning logs all the budget variables in the case of exhaustion).
+    This means `ask()` can still return additional trials after budget exhaustion.
+    SMAC now emits a runtime warning in this case and keeps this behaviour for backward compatibility.
+    If you want strict stopping in your loop, stop calling `ask()` when the optimizer reports no remaining budget (for example, `smac.optimizer.budget_exhausted` or `smac.optimizer.remaining_trials <= 0`)
+
 Notice: if you are exclusively using the ask-and-tell interface and do not use `smac.optimize()`, then smac no longer
 is responsible for the evaluation of the trials and therefore the Facade no longer will require a specified `target_algorithm` argument.
 

smac/main/smbo.py

@@ -79,6 +79,7 @@ def __init__(
         self._finished = False
         self._stop = False  # Gracefully stop SMAC
         self._callbacks: list[Callback] = []
+        self._warned_on_ask_after_budget_exhausted = False
 
         # Stats variables
         self._start_time: float | None = None
@@ -155,6 +156,16 @@ def ask(self) -> TrialInfo:
         """
         logger.debug("Calling ask...")
 
+        if self.budget_exhausted and not self._warned_on_ask_after_budget_exhausted:
+            logger.warning(
+                "ask() was called after the scenario budget was exhausted."
+                f"(remaining wallclock time: {self.remaining_walltime}, "
+                f"remaining cpu time: {self.remaining_cputime}, "
+                f"remaining trials: {self.remaining_trials}). "
+                "SMAC will continue returning trials for backward compatibility."
+            )
+            self._warned_on_ask_after_budget_exhausted = True
+
         for callback in self._callbacks:
             callback.on_ask_start(self)
 
@@ -371,6 +382,7 @@ def reset(self) -> None:
         self._used_target_function_walltime = 0
         self._used_target_function_cputime = 0
         self._finished = False
+        self._warned_on_ask_after_budget_exhausted = False
 
         # We also reset runhistory and intensifier here
         self._runhistory.reset()