Fix sweep model termination logic (#894)

* Fix logic in GlobalFixation and FocalDemeFixation
for cases where the mutation key has changed.

Fixes #893

* update change log

doc/misc/changelog.md

@@ -3,7 +3,17 @@
 Major changes are listed below.  Each release likely contains fiddling with back-end code,
 updates to latest `fwdpp` version, etc.
 
-## Next release
+## 0.17.1
+
+Bug fixes
+
+* Fix bug in fixation checking in `fwdpy11.conditional_models`.
+  Previous results were not incorrect.
+  Rather, they took too long to be obtained because some simulations did not terminate early enough.
+  Issue {issue}`893`
+  PR {pr}`894`
+
+  Miscellaneous
 
 - Improved exception message for invalid migrations during a simulation.
   PR {pr}`892`

fwdpy11/conditional_models/__init__.py

@@ -215,6 +215,7 @@ class SimulationStatus:
 
     For examples, see implementations of :class:`GlobalFixation` and :class:`FocalDemeFixation`.
     """
+
     should_terminate: bool = attr.ib(validator=attr.validators.instance_of(bool))
     condition_met: bool = attr.ib(validator=attr.validators.instance_of(bool))
 
@@ -241,7 +242,15 @@ def __call__(
         self, pop: fwdpy11.DiploidPopulation, index: int, key: tuple
     ) -> SimulationStatus:
         if pop.mutations[index].key != key:
-            return SimulationStatus(False, False)
+            # The key has changed, meaning the mutation is
+            # flagged for recycling.
+            # First, check if it is in the fixations list
+            for m in pop.fixations:
+                if m.key == key:
+                    # It is fixed, so we are done
+                    return SimulationStatus(True, False)
+            # The mutation is gone from the simulation
+            return SimulationStatus(True, False)
         if pop.mcounts[index] == 0:
             return SimulationStatus(True, False)
         if pop.mcounts[index] == 2 * pop.N:
@@ -262,7 +271,12 @@ class FocalDemeFixation:
     def __call__(self, pop: fwdpy11.DiploidPopulation, index, key) -> SimulationStatus:
         deme_sizes = pop.deme_sizes(as_dict=True)
         if pop.mutations[index].key != key:
-            return SimulationStatus(False, False)
+            # check for a global fixation
+            for m in pop.fixations:
+                if m.key == key:
+                    return SimulationStatus(True, False)
+            # The mutation is gone from the simulation
+            return SimulationStatus(True, False)
         if self.deme not in deme_sizes:
             return SimulationStatus(False, False)
         count = 0