7119: data loss with mistyped --basetemp

AUTHORS

@@ -221,6 +221,7 @@ Pedro Algarvio
 Philipp Loose
 Pieter Mulder
 Piotr Banaszkiewicz
+Prashant Anand
 Pulkit Goyal
 Punyashloka Biswal
 Quentin Pradet

changelog/7119.improvement.rst

@@ -0,0 +1,2 @@
+Exit with an error if the ``--basetemp`` argument is empty, the current working directory or parent directory of it.
+This is done to protect against accidental data loss, as any directory passed to this argument is cleared.

src/_pytest/main.py

@@ -1,4 +1,5 @@
 """ core implementation of testing process: init, session, runtest loop. """
+import argparse
 import fnmatch
 import functools
 import importlib
@@ -26,6 +27,7 @@
 from _pytest.config import UsageError
 from _pytest.fixtures import FixtureManager
 from _pytest.outcomes import exit
+from _pytest.pathlib import Path
 from _pytest.reports import CollectReport
 from _pytest.runner import collect_one_node
 from _pytest.runner import SetupState
@@ -167,6 +169,7 @@ def pytest_addoption(parser):
         "--basetemp",
         dest="basetemp",
         default=None,
+        type=validate_basetemp,
         metavar="dir",
         help=(
             "base temporary directory for this test run."
@@ -175,6 +178,34 @@ def pytest_addoption(parser):
     )
 
 
+def validate_basetemp(path: str) -> str:
+    # GH 7119
+    msg = "basetemp must not be empty, the current working directory or any parent directory of it"
+
+    # empty path
+    if not path:
+        raise argparse.ArgumentTypeError(msg)
+
+    def is_ancestor(base: Path, query: Path) -> bool:
+        """ return True if query is an ancestor of base, else False."""
+        if base == query:
+            return True
+        for parent in base.parents:
+            if parent == query:
+                return True
+        return False
+
+    # check if path is an ancestor of cwd
+    if is_ancestor(Path.cwd(), Path(path).absolute()):
+        raise argparse.ArgumentTypeError(msg)
+
+    # check symlinks for ancestors
+    if is_ancestor(Path.cwd().resolve(), Path(path).resolve()):
+        raise argparse.ArgumentTypeError(msg)
+
+    return path
+
+
 def wrap_session(
     config: Config, doit: Callable[[Config, "Session"], Optional[Union[int, ExitCode]]]
 ) -> Union[int, ExitCode]:

testing/test_main.py

@@ -1,7 +1,9 @@
+import argparse
 from typing import Optional
 
 import pytest
 from _pytest.config import ExitCode
+from _pytest.main import validate_basetemp
 from _pytest.pytester import Testdir
 
 
@@ -75,3 +77,24 @@ def pytest_sessionfinish():
         assert result.ret == ExitCode.NO_TESTS_COLLECTED
     assert result.stdout.lines[-1] == "collected 0 items"
     assert result.stderr.lines == ["Exit: exit_pytest_sessionfinish"]
+
+
+@pytest.mark.parametrize("basetemp", ["foo", "foo/bar"])
+def test_validate_basetemp_ok(tmp_path, basetemp, monkeypatch):
+    monkeypatch.chdir(str(tmp_path))
+    validate_basetemp(tmp_path / basetemp)
+
+
+@pytest.mark.parametrize("basetemp", ["", ".", ".."])
+def test_validate_basetemp_fails(tmp_path, basetemp, monkeypatch):
+    monkeypatch.chdir(str(tmp_path))
+    msg = "basetemp must not be empty, the current working directory or any parent directory of it"
+    with pytest.raises(argparse.ArgumentTypeError, match=msg):
+        if basetemp:
+            basetemp = tmp_path / basetemp
+        validate_basetemp(basetemp)
+
+
+def test_validate_basetemp_integration(testdir):
+    result = testdir.runpytest("--basetemp=.")
+    result.stderr.fnmatch_lines("*basetemp must not be*")