Add a look back constraint on spiral errors

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## 41.5.0 [#1205](https://github.com/openfisca/openfisca-core/pull/1205)
+
+#### New feature
+
+- Add a look back constraint on spiral errors
+
 ### 41.4.2 [#1203](https://github.com/openfisca/openfisca-core/pull/1203)
 
 #### Technical changes

openfisca_core/simulations/simulation.py

@@ -48,6 +48,8 @@ def __init__(
 
         # controls the spirals detection; check for performance impact if > 1
         self.max_spiral_loops: int = 1
+        self.max_spiral_lookback_months: int = 0
+
         self.memory_config = None
         self._data_storage_dir = None
 
@@ -400,8 +402,10 @@ def _check_for_cycle(self, variable: str, period):
             raise errors.CycleError(
                 "Circular definition detected on formula {}@{}".format(variable, period)
             )
-        spiral = len(previous_periods) >= self.max_spiral_loops
-        if spiral:
+
+        too_many_spirals = len(previous_periods) >= self.max_spiral_loops
+        too_backward = (previous_periods[0].date - period.date).in_months() > self.max_spiral_lookback_months if previous_periods and self.max_spiral_lookback_months > 0 else False
+        if too_many_spirals or too_backward:
             self.invalidate_spiral_variables(variable)
             message = "Quasicircular definition detected on formula {}@{} involving {}".format(
                 variable, period, self.tracer.stack
@@ -412,17 +416,9 @@ def invalidate_cache_entry(self, variable: str, period):
         self.invalidated_caches.add(Cache(variable, period))
 
     def invalidate_spiral_variables(self, variable: str):
-        # Visit the stack, from the bottom (most recent) up; we know that we'll find
-        # the variable implicated in the spiral (max_spiral_loops+1) times; we keep the
-        # intermediate values computed (to avoid impacting performance) but we mark them
-        # for deletion from the cache once the calculation ends.
-        count = 0
-        for frame in reversed(self.tracer.stack):
+        first_variable_occurrence = next(index for (index, frame) in enumerate(self.tracer.stack) if frame["name"] == variable)
+        for frame in self.tracer.stack[first_variable_occurrence:]:
             self.invalidate_cache_entry(str(frame["name"]), frame["period"])
-            if frame["name"] == variable:
-                count += 1
-                if count > self.max_spiral_loops:
-                    break
 
     # ----- Methods to access stored values ----- #
 

setup.py

@@ -67,7 +67,7 @@
 
 setup(
     name="OpenFisca-Core",
-    version="41.4.2",
+    version="41.5.0",
     author="OpenFisca Team",
     author_email="[email protected]",
     classifiers=[

tests/core/test_tracers.py

@@ -10,6 +10,7 @@
 from openfisca_country_template.variables.housing import HousingOccupancyStatus
 
 from openfisca_core.simulations import CycleError, Simulation, SpiralError
+from openfisca_core.periods import period
 from openfisca_core.tracers import (
     FullTracer,
     SimpleTracer,
@@ -28,13 +29,15 @@ class StubSimulation(Simulation):
     def __init__(self):
         self.exception = None
         self.max_spiral_loops = 1
+        self.max_spiral_lookback_months = 0
+        self.invalidated_cache_items = []
 
     def _calculate(self, variable, period):
         if self.exception:
             raise self.exception
 
     def invalidate_cache_entry(self, variable, period):
-        pass
+        self.invalidated_cache_items.append((variable, period))
 
     def purge_cache_of_invalid_values(self):
         pass
@@ -120,12 +123,15 @@ def test_cycle_error(tracer):
 def test_spiral_error(tracer):
     simulation = StubSimulation()
     simulation.tracer = tracer
-    tracer.record_calculation_start("a", 2017)
-    tracer.record_calculation_start("a", 2016)
-    tracer.record_calculation_start("a", 2015)
+    tracer.record_calculation_start("a", period(2017))
+    tracer.record_calculation_start("b", period(2016))
+    tracer.record_calculation_start("a", period(2016))
 
     with raises(SpiralError):
-        simulation._check_for_cycle("a", 2015)
+        simulation._check_for_cycle("a", period(2016))
+
+    assert len(simulation.invalidated_cache_items) == 3
+    assert len(tracer.stack) == 3
 
 
 def test_full_tracer_one_calculation(tracer):