fix: recover cached venvs from dangling package symlinks

python/private/python_bootstrap_template.txt

@@ -437,7 +437,14 @@ print(site.getsitepackages(["{venv_src}"])[-1])
     for venv_rel_path, link_to_rf_path in RUNTIME_VENV_SYMLINKS.items():
         venv_abs_path = join(venv, venv_rel_path)
         link_to = normpath(join(runfiles_root, link_to_rf_path))
-        os.makedirs(dirname(venv_abs_path), exist_ok=True)
+        venv_parent = dirname(venv_abs_path)
+        # A cached venv can leave this parent as a dangling link to an old EXTRACT_ROOT.
+        if os.path.islink(venv_parent):
+            try:
+                os.stat(venv_parent)
+            except FileNotFoundError:
+                os.unlink(venv_parent)
+        os.makedirs(venv_parent, exist_ok=True)
         _symlink_exist_ok(from_=venv_abs_path, to=link_to)
 
     # Do this last to handle non-relative symlinks artifacts

tests/bootstrap_impls/BUILD.bazel

@@ -140,6 +140,14 @@ pytest_test(
     ],
 )
 
+py_test(
+    name = "cached_venv_replaces_dangling_package_symlink_test",
+    srcs = ["cached_venv_dangling_symlink_test.py"],
+    data = ["//python/private:python_bootstrap_template.txt"],
+    main = "cached_venv_dangling_symlink_test.py",
+    deps = ["//python/runfiles"],
+)
+
 py_reconfig_test(
     name = "sys_path_order_bootstrap_system_python_test",
     srcs = ["sys_path_order_test.py"],

tests/bootstrap_impls/cached_venv_dangling_symlink_test.py

@@ -0,0 +1,85 @@
+"""Regression test for dangling runtime package links in persistent venvs."""
+
+from __future__ import annotations
+
+import os
+import pathlib
+import sys
+import tempfile
+import unittest
+
+from python.runfiles import runfiles
+
+
+def _load_bootstrap() -> dict:
+    r = runfiles.Create()
+    if r:
+        template_path = r.Rlocation(
+            "rules_python/python/private/python_bootstrap_template.txt"
+        )
+        assert template_path is not None
+        template = pathlib.Path(template_path)
+    else:
+        template = (
+            pathlib.Path(__file__).resolve().parents[2]
+            / "python/private/python_bootstrap_template.txt"
+        )
+    source = template.read_text(encoding="utf-8")
+    for placeholder, value in [
+        ("%shebang%", "#!/usr/bin/env python3"),
+        ("%stage2_bootstrap%", "unused.py"),
+        ("%runtime_venv_symlinks%", ""),
+    ]:
+        source = source.replace(placeholder, value)
+
+    bootstrap = {"__name__": "bootstrap_test"}
+    saved_path = sys.path[:]
+    try:
+        exec(compile(source, str(template), "exec"), bootstrap)
+    finally:
+        sys.path[:] = saved_path
+    return bootstrap
+
+
+class CachedVenvDanglingSymlinkTest(unittest.TestCase):
+    def test_replaces_dangling_package_link_before_creating_child_link(self) -> None:
+        bootstrap = _load_bootstrap()
+        with tempfile.TemporaryDirectory() as temp:
+            root = pathlib.Path(temp)
+            runfiles = root / "runfiles"
+            old_package = runfiles / "old/annotated_types"
+            old_package.mkdir(parents=True)
+            (old_package / "__init__.py").touch()
+            bootstrap.update(
+                EXTRACT_ROOT=str(root / "cache"),
+                PYTHON_BINARY="_main/_process.venv/Scripts/python.exe",
+                PYTHON_BINARY_ACTUAL=sys.executable,
+                RESOLVE_PYTHON_BINARY_AT_RUNTIME=False,
+                RUNTIME_VENV_SYMLINKS={
+                    "Lib/site-packages/annotated_types": "old/annotated_types",
+                },
+            )
+
+            bootstrap["_create_venv"](str(runfiles), [])
+            old_package.rename(root / "retired-package")
+
+            new_package = runfiles / "new/annotated_types"
+            new_package.mkdir(parents=True)
+            (new_package / "__init__.py").touch()
+            bootstrap["RUNTIME_VENV_SYMLINKS"] = {
+                "Lib/site-packages/annotated_types/__init__.py":
+                    "new/annotated_types/__init__.py",
+            }
+
+            bootstrap["_create_venv"](str(runfiles), [])
+
+            package = root / "cache/_main/_process.venv/Lib/site-packages/annotated_types"
+            package_init = package / "__init__.py"
+            self.assertTrue(package.is_dir())
+            self.assertFalse(package.is_symlink())
+            self.assertTrue(package_init.is_symlink())
+            self.assertTrue(os.path.samefile(package_init, new_package / "__init__.py"))
+
+
+if __name__ == "__main__":
+    unittest.main()