Merge "Improve `Rewriter` implementation" into main

diff --cc alembic/autogenerate/rewriter.py
index 02ff431c2a64041d8127be4517122529f0714b08,3efb499b366cf111f2d0cf4ded5a7c8726214744..8994dcf823cb3e40ddbab287cd7b80b166ae885b
--- 1/alembic/autogenerate/rewriter.py
--- 2/alembic/autogenerate/rewriter.py
+++ b/alembic/autogenerate/rewriter.py
@@@ -21,10 -20,13 +21,14 @@@ if TYPE_CHECKING
      from ..operations.ops import MigrationScript
      from ..operations.ops import ModifyTableOps
      from ..operations.ops import OpContainer
 -    from ..runtime.environment import _GetRevArg
 +    from ..operations.ops import UpgradeOps
      from ..runtime.migration import MigrationContext
 +    from ..script.revision import _GetRevArg
  
+ ProcessRevisionDirectiveFn = Callable[
+     ["MigrationContext", "_GetRevArg", List["MigrationScript"]], None
+ ]
+ 
  
  class Rewriter:
      """A helper object that allows easy 'rewriting' of ops streams.