bug#46397: 27.1; Cannot delete buffer pointing to a file in a path that includes a file

[Matt Armstrong]

Matt Armstrong <matt@rfc20.org> writes:

> "Peter" <craven@gmx.net> writes:
>
>> The following steps reproduce this:
>> - Make sure /tmp/tmp does not exist
>> - Open a buffer /tmp/tmp/foo.txt
>> - Make some changes to the buffer.
>> - Do *not* save the buffer or create the directory /tmp/tmp/
>> - Create /tmp/tmp as a *file* (not a directory)
>> - Try to kill the buffer.
>>
>> You will see the following error message:
>>
>> Unlocking file: Not a directory, /tmp/tmp/foo.txt
>>
>> I just want to kill the buffer, I don't want to save it.

[...]

> The backtrace is unsurprising:
>
> Debugger entered--Lisp error: (file-error "Unlocking file" "Not a directory" 
> "/private/tmp/tmp/test.txt")
>   kill-buffer("test.txt")
>   funcall-interactively(kill-buffer "test.txt")
>   call-interactively(kill-buffer nil nil)
>   command-execute(kill-buffer)

I found that this behavior was introduced by Paul Egger's commit
9dc306b1db0, discussed in Bug#37389.  I've cc'd Paul.

Paul's commit changed unlock_file() (from src/filelock.cc) to report
errors from unlink(), excempting only ENOENT. This bug demonstrates a
way to induce an ENOTDIR error. I've attached a patch that ignores
ENOTDIR as well, which is the most conservative fix I can think of. It
also seems in-line with Paul's original intent, since he was saying that
both ENOENT and ENOTDIR are usually "tame."

>From fc0b7f2595bd8680952f062d2dd5261f94394e1c Mon Sep 17 00:00:00 2001
From: Matt Armstrong <matt@rfc20.org>
Date: Tue, 9 Feb 2021 16:14:28 -0800
Subject: [PATCH] Ignore ENOTDIR errors from unlink().

* src/filelock.c (unlock_file): Ignore ENOTDIR errors from unlink().
---
 src/filelock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/filelock.c b/src/filelock.c
index 35baa0c666..af5683f365 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -731,7 +731,8 @@ unlock_file (Lisp_Object fn)
   MAKE_LOCK_NAME (lfname, fn);
 
   int err = current_lock_owner (0, lfname);
-  if (err == -2 && unlink (lfname) != 0 && errno != ENOENT)
+  if (err == -2 && unlink (lfname) != 0
+      && (errno != ENOENT && errno != ENOTDIR))
     err = errno;
   if (0 < err)
     report_file_errno ("Unlocking file", filename, err);
-- 
2.30.0