fix: don't reset context.scratch between files

libcst/codemod/_cli.py

@@ -14,6 +14,7 @@
 import sys
 import time
 import traceback
+from copy import deepcopy
 from dataclasses import dataclass, replace
 from multiprocessing import cpu_count, Pool
 from pathlib import Path
@@ -214,6 +215,7 @@ def _execute_transform(  # noqa: C901
     transformer: Codemod,
     filename: str,
     config: ExecutionConfig,
+    scratch: Dict[str, object],
 ) -> ExecutionResult:
     for pattern in config.blacklist_patterns:
         if re.fullmatch(pattern, filename):
@@ -251,7 +253,7 @@ def _execute_transform(  # noqa: C901
         transformer.context = replace(
             transformer.context,
             filename=filename,
-            scratch={},
+            scratch=deepcopy(scratch),
         )
 
         # determine the module and package name for this file
@@ -634,6 +636,7 @@ def parallel_exec_transform_with_prettyprint(  # noqa: C901
                 "transformer": transform,
                 "filename": filename,
                 "config": config,
+                "scratch": transform.context.scratch,
             }
             for filename in files
         ]

libcst/tests/test_e2e.py

@@ -2,7 +2,7 @@
 import os
 from pathlib import Path
 from tempfile import TemporaryDirectory
-from typing import Generator
+from typing import Dict, Generator
 from unittest import TestCase
 
 from libcst import BaseExpression, Call, matchers as m, Name
@@ -16,7 +16,14 @@
 
 
 class PrintToPPrintCommand(VisitorBasedCodemodCommand):
+    def __init__(self, context: CodemodContext, **kwargs: Dict[str, object]) -> None:
+        super().__init__(context, **kwargs)
+        self.context.scratch["PPRINT_WAS_HERE"] = True
+
     def leave_Call(self, original_node: Call, updated_node: Call) -> BaseExpression:
+        if not self.context.scratch["PPRINT_WAS_HERE"]:
+            raise AssertionError("Scratch space lost")
+
         if m.matches(updated_node, m.Call(func=m.Name("print"))):
             AddImportsVisitor.add_needed_import(
                 self.context,