Fix crashing under squashfuse_ll read-only mounts (#12301)

Fixes #12300

AUTHORS

@@ -441,6 +441,7 @@ Yao Xiao
 Yoav Caspi
 Yuliang Shao
 Yusuke Kadowaki
+Yutian Li
 Yuval Shimon
 Zac Hatfield-Dodds
 Zachary Kneupper

changelog/12300.bugfix.rst

@@ -0,0 +1 @@
+Fixed handling of 'Function not implemented' error under squashfuse_ll, which is a different way to say that the mountpoint is read-only.

src/_pytest/assertion/rewrite.py

@@ -1171,7 +1171,10 @@ def try_makedirs(cache_dir: Path) -> bool:
         return False
     except OSError as e:
         # as of now, EROFS doesn't have an equivalent OSError-subclass
-        if e.errno == errno.EROFS:
+        #
+        # squashfuse_ll returns ENOSYS "OSError: [Errno 38] Function not
+        # implemented" for a read-only error
+        if e.errno in {errno.EROFS, errno.ENOSYS}:
             return False
         raise
     return True

testing/test_assertrewrite.py

@@ -1972,6 +1972,11 @@ def fake_mkdir(p, exist_ok=False, *, exc):
     monkeypatch.setattr(os, "makedirs", partial(fake_mkdir, exc=err))
     assert not try_makedirs(p)
 
+    err = OSError()
+    err.errno = errno.ENOSYS
+    monkeypatch.setattr(os, "makedirs", partial(fake_mkdir, exc=err))
+    assert not try_makedirs(p)
+
     # unhandled OSError should raise
     err = OSError()
     err.errno = errno.ECHILD