faster target phase

hypothesis-python/RELEASE.rst

@@ -8,3 +8,6 @@ as well continue running the test!
 
 Because we now finish running a few more examples for affected tests, this
 might be a slight slowdown - but correspondingly more likely to find a bug.
+
+We've also applied similar tricks to the :ref:`target phase <phases>`, where
+they are a pure performance improvement for affected tests.

hypothesis-python/src/hypothesis/core.py

@@ -1056,7 +1056,7 @@ def _execute_once_for_engine(self, data: ConjectureData) -> None:
                     phase = "shrink"
                 elif runner := getattr(self, "_runner", None):
                     phase = runner._current_phase
-                else:
+                else:  # pragma: no cover  # in case of messing with internals
                     phase = "unknown"
                 tc = make_testcase(
                     start_timestamp=self._start_timestamp,

hypothesis-python/src/hypothesis/internal/conjecture/engine.py

@@ -129,6 +129,7 @@ def __init__(
 
         # Global dict of per-phase statistics, and a list of per-call stats
         # which transfer to the global dict at the end of each phase.
+        self._current_phase = "(not a phase)"
         self.statistics = {}
         self.stats_per_test_case = []
 
@@ -887,7 +888,8 @@ def optimise_targets(self):
             if any_improvements:
                 continue
 
-            self.pareto_optimise()
+            if self.best_observed_targets:
+                self.pareto_optimise()
 
             if prev_calls == self.call_count:
                 break
@@ -1015,6 +1017,7 @@ def new_shrinker(self, example, predicate=None, allow_transition=None):
             predicate,
             allow_transition=allow_transition,
             explain=Phase.explain in self.settings.phases,
+            in_target_phase=self._current_phase == "target",
         )
 
     def cached_test_function(self, buffer, *, error_on_discard=False, extend=0):

hypothesis-python/src/hypothesis/internal/conjecture/pareto.py

@@ -317,7 +317,7 @@ def allow_transition(source, destination):
                     # If ``destination`` dominates ``source`` then ``source``
                     # must be dominated in the front - either ``destination`` is in
                     # the front, or it was not added to it because it was
-                    # dominated by something in it.,
+                    # dominated by something in it.
                     try:
                         self.front.front.remove(source)
                     except ValueError:

hypothesis-python/src/hypothesis/internal/conjecture/shrinker.py

@@ -271,6 +271,7 @@ def __init__(
         *,
         allow_transition: bool,
         explain: bool,
+        in_target_phase: bool = False,
     ):
         """Create a shrinker for a particular engine, with a given starting
         point and predicate. When shrink() is called it will attempt to find an
@@ -309,6 +310,14 @@ def __init__(
         # testing and learning purposes.
         self.extra_dfas: Dict[str, ConcreteDFA] = {}
 
+        # Because the shrinker is also used to `pareto_optimise` in the target phase,
+        # we sometimes want to allow extending buffers instead of aborting at the end.
+        if in_target_phase:
+            from hypothesis.internal.conjecture.engine import BUFFER_SIZE
+
+            self.__extend = BUFFER_SIZE
+        else:
+            self.__extend = 0
         self.should_explain = explain
 
     @derived_value  # type: ignore
@@ -417,7 +426,7 @@ def cached_test_function(self, buffer):
         with status >= INVALID that would result from running this buffer."""
 
         buffer = bytes(buffer)
-        result = self.engine.cached_test_function(buffer)
+        result = self.engine.cached_test_function(buffer, extend=self.__extend)
         self.incorporate_test_data(result)
         if self.calls - self.calls_at_last_shrink >= self.max_stall:
             raise StopShrinking