Prevent --update-functional-output from deleting or overwriting fallback versioned output files for other Python versions.

pylint/testutils/functional/lint_module_output_update.py

@@ -31,6 +31,8 @@ def _check_output_text(
         actual_output: list[OutputLine],
     ) -> None:
         """Overwrite or remove the expected output file based on actual output."""
+        if self._test_file.expected_output_is_fallback:
+            return
         # Remove the expected file if no output is actually emitted and a file exists
         if not actual_output:
             if os.path.exists(self._test_file.expected_output):

pylint/testutils/functional/test_file.py

@@ -103,6 +103,15 @@ def module(self) -> str:
 
     @property
     def expected_output(self) -> str:
+        output, _ = self._resolve_expected_output()
+        return output
+
+    @property
+    def expected_output_is_fallback(self) -> bool:
+        _, is_fallback = self._resolve_expected_output()
+        return is_fallback
+
+    def _resolve_expected_output(self) -> tuple[str, bool]:
         files = [
             p.stem
             for p in Path(self._directory).glob(f"{split(self.base)[-1]}.[0-9]*.txt")
@@ -115,8 +124,11 @@ def expected_output(self) -> str:
         for opt in sorted(output_options, reverse=True):
             if _CURRENT_VERSION >= opt:
                 str_opt = "".join([str(s) for s in opt])
-                return join(self._directory, f"{self.base}.{str_opt}.txt")
-        return join(self._directory, self.base + ".txt")
+                return (
+                    join(self._directory, f"{self.base}.{str_opt}.txt"),
+                    _CURRENT_VERSION != opt,
+                )
+        return join(self._directory, self.base + ".txt"), False
 
     @property
     def source(self) -> str:

tests/testutils/test_lint_module_output_update.py

@@ -9,6 +9,7 @@
 import shutil
 from collections.abc import Callable
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
 
@@ -71,6 +72,48 @@ def test_lint_module_output_update_remove_useless_txt(
     assert not expected_output_file.exists()
 
 
+def test_lint_module_output_update_does_not_remove_fallback_versioned_output(
+    lint_module_fixture: Callable[[str], tuple[Path, Path, LintModuleOutputUpdate]],
+) -> None:
+    """Fallback versioned expected output should not be deleted on update."""
+    filename, expected_output_file, lmou = lint_module_fixture("fine_name")
+    expected_output_file.write_text("", encoding="utf8")
+    filename.write_text("", encoding="utf8")
+    fallback_output_file = filename.with_suffix(".313.txt")
+    fallback_output_file.write_text("old output\n", encoding="utf8")
+
+    with patch(
+        "pylint.testutils.functional.test_file._CURRENT_VERSION",
+        new=(3, 14),
+    ):
+        assert Path(lmou._test_file.expected_output) == fallback_output_file
+        lmou.runTest()
+    assert expected_output_file.exists()
+    assert fallback_output_file.exists()
+
+
+def test_lint_module_output_update_does_not_overwrite_fallback_versioned_output(
+    lint_module_fixture: Callable[[str], tuple[Path, Path, LintModuleOutputUpdate]],
+) -> None:
+    """Fallback versioned expected output should not be overwritten on update."""
+    filename, expected_output_file, lmou = lint_module_fixture("foo")
+    expected_output_file.write_text("", encoding="utf8")
+    filename.write_text("# [disallowed-name]\n", encoding="utf8")
+    fallback_output_file = filename.with_suffix(".313.txt")
+    fallback_output_file.write_text("old output\n", encoding="utf8")
+
+    with patch(
+        "pylint.testutils.functional.test_file._CURRENT_VERSION",
+        new=(3, 14),
+    ):
+        assert Path(lmou._test_file.expected_output) == fallback_output_file
+        lmou.runTest()
+
+    assert expected_output_file.exists()
+    assert fallback_output_file.exists()
+    assert fallback_output_file.read_text(encoding="utf8") == "old output\n"
+
+
 @pytest.mark.parametrize(
     "directory_path", DIRECTORIES, ids=[str(p) for p in DIRECTORIES]
 )