bug#64821: 30.0.50; write-region errs when overwriting an already open file

["Mattias Engdegård" <mattias.engdegard@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 131 bytes --]

The change on master (8955853368) causes filelock-tests to fail; see attached log.
This is on macOS with an out-of-tree build.


[-- Attachment #2: filelock-tests.log --]
[-- Type: application/octet-stream, Size: 2747 bytes --]

  GEN      src/filelock-tests.log
Running 6 tests (2023-07-27 17:03:57+0200, selector `(not (or (tag :unstable) (tag :nativecomp)))')
(Shell command succeeded with no output)
Test filelock-tests-detect-external-change backtrace:
  userlock--check-content-unchanged("/private/var/folders/qy/zstv16390
  userlock--ask-user-about-supersession-threat("/private/var/folders/q
  insert("bar")
  (let ((create-lockfiles cl)) (write-region "foo" nil (buffer-file-na
  (save-current-buffer (let ((create-lockfiles cl)) (write-region "foo
  (unwind-protect (save-current-buffer (let ((create-lockfiles cl)) (w
  (progn (progn (setq buffer-file-name name) (setq buffer-file-truenam
  (unwind-protect (progn (progn (setq buffer-file-name name) (setq buf
  (save-current-buffer (set-buffer temp-buffer) (unwind-protect (progn
  (let ((temp-buffer (generate-new-buffer " *temp*" t))) (save-current
  (let ((name (concat (file-name-as-directory temp-dir) "userfile")) (
  (progn (let ((name (concat (file-name-as-directory temp-dir) "userfi
  (unwind-protect (progn (let ((name (concat (file-name-as-directory t
  (let* ((coding-system-for-write nil) (temp-file (file-name-as-direct
  (let ((cl (car tail))) (let* ((coding-system-for-write nil) (temp-fi
  (while tail (let ((cl (car tail))) (let* ((coding-system-for-write n
  (let ((tail '(t nil))) (while tail (let ((cl (car tail))) (let* ((co
  (closure (t) nil (let* ((fn-101 #'not) (args-102 (condition-case err
  ert--run-test-internal(#s(ert--test-execution-info :test #s(ert-test
  ert-run-test(#s(ert-test :name filelock-tests-detect-external-change
  ert-run-or-rerun-test(#s(ert--stats :selector (not ...) :tests [... 
  ert-run-tests((not (or (tag :unstable) (tag :nativecomp))) #f(compil
  ert-run-tests-batch((not (or (tag :unstable) (tag :nativecomp))))
  ert-run-tests-batch-and-exit((not (or (tag :unstable) (tag :nativeco
  eval((ert-run-tests-batch-and-exit '(not (or (tag :unstable) (tag :n
  command-line-1(("-L" ":../../emacs/test" "-l" "ert" "-l" "src/filelo
  command-line()
  normal-top-level()
Test filelock-tests-detect-external-change condition:
    (wrong-type-argument stringp nil)
   FAILED  1/6  filelock-tests-detect-external-change (0.024295 sec) at ../../emacs/test/src/filelock-tests.el:173
   passed  2/6  filelock-tests-file-locked-p-spoiled (0.001322 sec)
   passed  3/6  filelock-tests-kill-buffer-spoiled (0.000714 sec)
   passed  4/6  filelock-tests-lock-spoiled (0.000609 sec)
   passed  5/6  filelock-tests-lock-unlock-no-errors (0.001055 sec)
   passed  6/6  filelock-tests-unlock-spoiled (0.000917 sec)

Ran 6 tests, 5 results as expected, 1 unexpected (2023-07-27 17:03:58+0200, 0.274700 sec)

1 unexpected results:
   FAILED  filelock-tests-detect-external-change

[-- Attachment #3: Type: text/plain, Size: 2 bytes --]