Rely on weight_windows_file implying weight windows are enabled

With the auto-enable behavior cherry-picked from develop (#4007),
convert_to_multigroup and the bootstrap test no longer need to set
weight_windows_on explicitly alongside the file.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

openmc/model/model.py

@@ -2701,8 +2701,8 @@ class Model:
             (fission treated as capture). If the resolved settings include a
             ``weight_windows_file`` (e.g., ``"weight_windows.h5"``), the
             ``"material_wise"`` method loads and applies those weight
-            windows during the continuous energy generation simulation
-            (``weight_windows_on`` is enabled automatically). Applying
+            windows during the continuous energy generation simulation.
+            Applying
             weight windows allows the simulation to obtain tallies -- and
             thus nonzero cross sections -- for materials located far from
             the source, for example behind a thick shield, which an analog
@@ -2792,24 +2792,23 @@ class Model:
             settings.run_mode = 'fixed source'
 
         # A weight windows file on the generation settings is loaded and
-        # applied during the "material_wise" method's continuous energy
-        # simulation of the original geometry, allowing materials far from
-        # the source -- which an analog simulation may struggle to reach --
-        # to still be tallied, and thus obtain nonzero cross sections. The
+        # applied (specifying a file turns weight windows on) during the
+        # "material_wise" method's continuous energy simulation of the
+        # original geometry, allowing materials far from the source --
+        # which an analog simulation may struggle to reach -- to still be
+        # tallied, and thus obtain nonzero cross sections. The
         # "stochastic_slab" and "infinite_medium" methods use simplified
         # surrogate geometries for which weight windows defined over the
         # original geometry are neither applicable nor needed.
-        if settings.weight_windows_file is not None:
-            if method == "material_wise":
-                settings.weight_windows_on = True
-            else:
-                warnings.warn(
-                    'The weight windows file set on the generation settings '
-                    'is only applicable to the "material_wise" MGXS '
-                    f'generation method and will be ignored for the '
-                    f'"{method}" method.'
-                )
-                settings.weight_windows_file = None
+        if settings.weight_windows_file is not None and \
+                method != "material_wise":
+            warnings.warn(
+                'The weight windows file set on the generation settings '
+                'is only applicable to the "material_wise" MGXS '
+                f'generation method and will be ignored for the '
+                f'"{method}" method.'
+            )
+            settings.weight_windows_file = None
 
         # Do all work (including MGXS generation) in a temporary directory
         # to avoid polluting the working directory with residual XML files

tests/regression_tests/random_ray_auto_convert_bootstrap/inputs_true.dat

@@ -61,7 +61,6 @@
         <domain_ids>1</domain_ids>
       </constraints>
     </source>
-    <weight_windows_on>true</weight_windows_on>
     <weight_windows_file>weight_windows.h5</weight_windows_file>
     <weight_window_checkpoints>
       <collision>true</collision>

tests/regression_tests/random_ray_auto_convert_bootstrap/test.py

@@ -91,7 +91,6 @@ def test_random_ray_auto_convert_bootstrap():
     # Run the continuous energy model with the improved weight windows,
     # tallying the flux in every region
     model.settings.weight_windows_file = 'weight_windows.h5'
-    model.settings.weight_windows_on = True
     model.settings.particles = 20
     model.settings.batches = 10
     tally = openmc.Tally(name='flux')

tests/unit_tests/test_model.py

@@ -1169,13 +1169,12 @@ def test_convert_to_multigroup_settings_weight_windows(run_in_tmpdir, monkeypatc
     gen = _capture_generation_settings(
         monkeypatch, model, method='material_wise', settings=user)
 
-    # A weight windows file on the generation settings is applied to the
-    # "material_wise" generation run with weight windows turned on
+    # A weight windows file on the generation settings is passed through to
+    # the "material_wise" generation run (specifying a file turns weight
+    # windows on at run time)
     assert gen.weight_windows_file == ww_path
-    assert gen.weight_windows_on is True
     # The caller's object is never mutated
     assert user.weight_windows_file == ww_path
-    assert user.weight_windows_on is None
 
     # The surrogate-geometry methods ignore the file with a warning
     with pytest.warns(UserWarning, match='material_wise'):