Removed in_between from Operation.reduce()'s signature.

It isn't used since FieldOperation.references_model() takes into
account models referenced by the field it's operating on.

django/db/migrations/operations/base.py

@@ -113,7 +113,7 @@ class Operation:
 
         return router.allow_migrate_model(connection_alias, model)
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         """
         Return either a list of operations the actual operation should be
         replaced with or a boolean that indicates whether or not the specified

django/db/migrations/operations/fields.py

@@ -60,9 +60,9 @@ class FieldOperation(Operation):
                     return True
         return False
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         return (
-            super().reduce(operation, in_between, app_label=app_label) or
+            super().reduce(operation, app_label=app_label) or
             not operation.references_field(self.model_name, self.name, app_label)
         )
 
@@ -122,7 +122,7 @@ class AddField(FieldOperation):
     def describe(self):
         return "Add field %s to %s" % (self.name, self.model_name)
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if isinstance(operation, FieldOperation) and self.is_same_field_operation(operation):
             if isinstance(operation, AlterField):
                 return [
@@ -142,7 +142,7 @@ class AddField(FieldOperation):
                         field=self.field,
                     ),
                 ]
-        return super().reduce(operation, in_between, app_label=app_label)
+        return super().reduce(operation, app_label=app_label)
 
 
 class RemoveField(FieldOperation):
@@ -186,11 +186,11 @@ class RemoveField(FieldOperation):
     def describe(self):
         return "Remove field %s from %s" % (self.name, self.model_name)
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         from .models import DeleteModel
         if isinstance(operation, DeleteModel) and operation.name_lower == self.model_name_lower:
             return [operation]
-        return super().reduce(operation, in_between, app_label=app_label)
+        return super().reduce(operation, app_label=app_label)
 
 
 class AlterField(FieldOperation):
@@ -256,7 +256,7 @@ class AlterField(FieldOperation):
     def describe(self):
         return "Alter field %s on %s" % (self.name, self.model_name)
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if isinstance(operation, RemoveField) and self.is_same_field_operation(operation):
             return [operation]
         elif isinstance(operation, RenameField) and self.is_same_field_operation(operation):
@@ -268,7 +268,7 @@ class AlterField(FieldOperation):
                     field=self.field,
                 ),
             ]
-        return super().reduce(operation, in_between, app_label=app_label)
+        return super().reduce(operation, app_label=app_label)
 
 
 class RenameField(FieldOperation):
@@ -383,7 +383,7 @@ class RenameField(FieldOperation):
             name.lower() == self.new_name_lower
         )
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if (isinstance(operation, RenameField) and
                 self.is_same_model_operation(operation) and
                 self.new_name_lower == operation.old_name_lower):
@@ -397,6 +397,6 @@ class RenameField(FieldOperation):
         # Skip `FieldOperation.reduce` as we want to run `references_field`
         # against self.new_name.
         return (
-            super(FieldOperation, self).reduce(operation, in_between, app_label=app_label) or
+            super(FieldOperation, self).reduce(operation, app_label=app_label) or
             not operation.references_field(self.model_name, self.new_name, app_label)
         )

django/db/migrations/operations/models.py

@@ -31,9 +31,9 @@ class ModelOperation(Operation):
     def references_model(self, name, app_label=None):
         return name.lower() == self.name_lower
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         return (
-            super().reduce(operation, in_between, app_label=app_label) or
+            super().reduce(operation, app_label=app_label) or
             not operation.references_model(self.name, app_label)
         )
 
@@ -117,7 +117,7 @@ class CreateModel(ModelOperation):
                 return True
         return False
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if (isinstance(operation, DeleteModel) and
                 self.name_lower == operation.name_lower and
                 not self.options.get("proxy", False)):
@@ -193,7 +193,7 @@ class CreateModel(ModelOperation):
                         managers=self.managers,
                     ),
                 ]
-        return super().reduce(operation, in_between, app_label=app_label)
+        return super().reduce(operation, app_label=app_label)
 
 
 class DeleteModel(ModelOperation):
@@ -368,7 +368,7 @@ class RenameModel(ModelOperation):
     def describe(self):
         return "Rename model %s to %s" % (self.old_name, self.new_name)
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if (isinstance(operation, RenameModel) and
                 self.new_name_lower == operation.old_name_lower):
             return [
@@ -380,7 +380,7 @@ class RenameModel(ModelOperation):
         # Skip `ModelOperation.reduce` as we want to run `references_model`
         # against self.new_name.
         return (
-            super(ModelOperation, self).reduce(operation, in_between, app_label=app_label) or
+            super(ModelOperation, self).reduce(operation, app_label=app_label) or
             not operation.references_model(self.new_name, app_label)
         )
 
@@ -434,26 +434,26 @@ class AlterModelTable(ModelOperation):
             self.table if self.table is not None else "(default)"
         )
 
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if isinstance(operation, (AlterModelTable, DeleteModel)) and self.name_lower == operation.name_lower:
             return [operation]
-        return super().reduce(operation, in_between, app_label=app_label)
+        return super().reduce(operation, app_label=app_label)
 
 
 class ModelOptionOperation(ModelOperation):
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if isinstance(operation, (self.__class__, DeleteModel)) and self.name_lower == operation.name_lower:
             return [operation]
-        return super().reduce(operation, in_between, app_label=app_label)
+        return super().reduce(operation, app_label=app_label)
 
 
 class FieldRelatedOptionOperation(ModelOptionOperation):
-    def reduce(self, operation, in_between, app_label=None):
+    def reduce(self, operation, app_label=None):
         if (isinstance(operation, FieldOperation) and
                 self.name_lower == operation.model_name_lower and
                 not self.references_field(operation.model_name, operation.name)):
             return [operation, self]
-        return super().reduce(operation, in_between, app_label=app_label)
+        return super().reduce(operation, app_label=app_label)
 
 
 class AlterUniqueTogether(FieldRelatedOptionOperation):

django/db/migrations/optimizer.py

@@ -46,12 +46,12 @@ class MigrationOptimizer:
             # Compare it to each operation after it
             for j, other in enumerate(operations[i + 1:]):
                 in_between = operations[i + 1:i + j + 1]
-                result = operation.reduce(other, in_between, app_label)
+                result = operation.reduce(other, app_label)
                 if isinstance(result, list):
                     if right:
                         new_operations.extend(in_between)
                         new_operations.extend(result)
-                    elif all(op.reduce(other, [], app_label) is True for op in in_between):
+                    elif all(op.reduce(other, app_label) is True for op in in_between):
                         # Perform a left reduction if all of the in-between
                         # operations can optimize through other.
                         new_operations.extend(result)