Fix handling recursive symlinks

When pytest was run on a directory containing a recursive symlink it failed
with ELOOP as the library was not able to determine the type of the
direntry:

src/_pytest/main.py:685: in collect
    if not direntry.is_file():
E   OSError: [Errno 40] Too many levels of symbolic links: '/home/florian/proj/pytest/tests/recursive'

This is fixed by handling ELOOP and other errors in the visit function in
pathlib.py, so the entries whose is_file() call raises an OSError with the
pre-defined list of error numbers will be exluded from the result.

The _ignore_errors function was copied from Lib/pathlib.py of cpython 3.9.

Fixes #7951

Author: csernazs

AUTHORS

@@ -314,3 +314,4 @@ Xuecong Liao
 Yoav Caspi
 Zac Hatfield-Dodds
 Zoltán Máté
+Zsolt Cserna

changelog/7951.bugfix.rst

@@ -0,0 +1 @@
+Fixed handling of recursive symlinks when collecting tests.

src/_pytest/pathlib.py

@@ -9,6 +9,10 @@
 import uuid
 import warnings
 from enum import Enum
+from errno import EBADF
+from errno import ELOOP
+from errno import ENOENT
+from errno import ENOTDIR
 from functools import partial
 from os.path import expanduser
 from os.path import expandvars
@@ -37,6 +41,24 @@
 
 _AnyPurePath = TypeVar("_AnyPurePath", bound=PurePath)
 
+# The following function, variables and comments were
+# copied from cpython 3.9 Lib/pathlib.py file.
+
+# EBADF - guard against macOS `stat` throwing EBADF
+_IGNORED_ERRORS = (ENOENT, ENOTDIR, EBADF, ELOOP)
+
+_IGNORED_WINERRORS = (
+    21,  # ERROR_NOT_READY - drive exists but is not accessible
+    1921,  # ERROR_CANT_RESOLVE_FILENAME - fix for broken symlink pointing to itself
+)
+
+
+def _ignore_error(exception):
+    return (
+        getattr(exception, "errno", None) in _IGNORED_ERRORS
+        or getattr(exception, "winerror", None) in _IGNORED_WINERRORS
+    )
+
 
 def get_lock_path(path: _AnyPurePath) -> _AnyPurePath:
     return path.joinpath(".lock")
@@ -555,8 +577,23 @@ def visit(
 
     Entries at each directory level are sorted.
     """
-    entries = sorted(os.scandir(path), key=lambda entry: entry.name)
+
+    # Skip entries with symlink loops and other brokenness, so the caller doesn't
+    # have to deal with it.
+    entries = []
+    for entry in os.scandir(path):
+        try:
+            entry.is_file()
+        except OSError as err:
+            if _ignore_error(err):
+                continue
+            raise
+        entries.append(entry)
+
+    entries.sort(key=lambda entry: entry.name)
+
     yield from entries
+
     for entry in entries:
         if entry.is_dir(follow_symlinks=False) and recurse(entry):
             yield from visit(entry.path, recurse)

testing/test_collection.py

@@ -1404,3 +1404,17 @@ def a(): return 4
     result = testdir.runpytest()
     # Not INTERNAL_ERROR
     assert result.ret == ExitCode.INTERRUPTED
+
+
+def test_does_not_crash_on_recursive_symlink(testdir: Testdir) -> None:
+    """Regression test for an issue around recursive symlinks (#7951)."""
+    symlink_or_skip("recursive", testdir.tmpdir.join("recursive"))
+    testdir.makepyfile(
+        """
+        def test_foo(): assert True
+        """
+    )
+    result = testdir.runpytest()
+
+    assert result.ret == ExitCode.OK
+    assert result.parseoutcomes() == {"passed": 1}

testing/test_pathlib.py

@@ -17,6 +17,8 @@
 from _pytest.pathlib import ImportPathMismatchError
 from _pytest.pathlib import maybe_delete_a_numbered_dir
 from _pytest.pathlib import resolve_package_path
+from _pytest.pathlib import symlink_or_skip
+from _pytest.pathlib import visit
 
 
 class TestFNMatcherPort:
@@ -401,3 +403,14 @@ def test_commonpath() -> None:
     assert commonpath(subpath, path) == path
     assert commonpath(Path(str(path) + "suffix"), path) == path.parent
     assert commonpath(path, path.parent.parent) == path.parent.parent
+
+
+def test_visit_ignores_errors(tmpdir) -> None:
+    symlink_or_skip("recursive", tmpdir.join("recursive"))
+    tmpdir.join("foo").write_binary(b"")
+    tmpdir.join("bar").write_binary(b"")
+
+    assert [entry.name for entry in visit(tmpdir, recurse=lambda entry: False)] == [
+        "bar",
+        "foo",
+    ]