bug#52451: 27.1; jka-compr-write-region produces wrong type argument error

["Braun Gábor" <braungb88@gmail.com>]

Hi,

Start Emacs via the command

 emacs -Q --batch -l jka-compr.el --eval '(let ((jka-compr-really-do-compress 
t) (debug-on-error t)) (jka-compr-write-region "foo" nil "/tmp/test.gz"))'        


This should run without any error.
Instead the following appears on the terminal:


uncompressing jka-compr.el.gz...
uncompressing jka-compr.el.gz...done
Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  -(nil "foo")
  (= (- end start) (buffer-size))
  (or (null start) (= (- end start) (buffer-size)))
  (and jka-compr-really-do-compress (or (null start) (= (- end start) (buffer-
size))))
  (if (and jka-compr-really-do-compress (or (null start) (= (- end start) 
(buffer-size)))) (setq magic nil))
  (let* ((filename (expand-file-name file)) (visit-file (if (stringp visit) 
(expand-file-name visit) filename)) (info (jka-compr-get-compression-info visit-
file)) (magic (and info (jka-compr-info-file-magic-bytes info)))) (if (and jka-
compr-really-do-compress (or (null start) (= (- end start) (buffer-size)))) 
(setq magic nil)) (if (and info (not (and magic (equal (if (stringp start) 
(substring start 0 ...) (let* ... ...)) magic)))) (let ((can-append (jka-
compr-info-can-append info)) (compress-program (jka-compr-info-compress-
program info)) (compress-message (jka-compr-info-compress-message info)) 
(compress-args (jka-compr-info-compress-args info)) (base-name (file-name-
nondirectory visit-file)) temp-file temp-buffer (coding-system-used last-coding-
system-used)) (or compress-program (error "No compression program defined")) 
(setq temp-buffer (get-buffer-create " *jka-compr-wr-temp*")) (save-current-
buffer (set-buffer temp-buffer) (widen) (erase-buffer)) (if (and append (not can-
append) (file-exists-p filename)) (let* ((local-copy (file-local-copy filename)) 
(local-file (or local-copy filename))) (setq temp-file local-file)) (setq temp-file 
(jka-compr-make-temp-name))) (and compress-message jka-compr-verbose (message 
"%s %s..." compress-message base-name)) (jka-compr-run-real-handler 'write-
region (list start end temp-file t 'dont)) (setq coding-system-used last-
coding-system-used) (let ((coding-system-for-read 'no-conversion)) (jka-compr-
call-process compress-program (concat compress-message " " base-name) temp-file 
temp-buffer nil compress-args)) (save-current-buffer (set-buffer temp-buffer) (let 
((coding-system-for-write 'no-conversion)) (jka-compr-run-real-handler 'write-
region (list (point-min) (point-max) filename (and append can-append) 'dont 
lockname mustbenew)) (erase-buffer))) (delete-file temp-file) (and compress-
message jka-compr-verbose (message "%s %s...done" compress-message base-
name)) (cond ((eq visit t) (setq buffer-file-name filename) (setq jka-compr-
really-do-compress t) (set-visited-file-modtime)) ((stringp visit) (setq buffer-
file-name visit) (let ((buffer-file-name filename)) (set-visited-file-modtime)))) 
(and (or (eq visit t) (eq visit nil) (stringp visit)) (message "Wrote %s" 
visit-file)) (setq last-coding-system-used coding-system-used) nil) (jka-compr-
run-real-handler 'write-region (list start end filename append visit lockname 
mustbenew))))
  jka-compr-write-region("foo" nil "/tmp/test.gz")
  (let ((jka-compr-really-do-compress t) (debug-on-error t)) (jka-compr-write-
region "foo" nil "/tmp/test.gz"))
  eval((let ((jka-compr-really-do-compress t) (debug-on-error t)) (jka-compr-
write-region "foo" nil "/tmp/test.gz")) t)
  command-line-1(("-l" "jka-compr.el" "--eval" "(let ((jka-compr-really-do-
compress t) (debug-on-e..."))
  command-line()
  normal-top-level()


My guess is that the debugger refers to the following snippet
in function `jka-commpr-write-region':

    ;; If we uncompressed this file when visiting it,
    ;; then recompress it when writing it
    ;; even if the contents look compressed already.
    (if (and jka-compr-really-do-compress
             (or (null start)
                 (= (- end start) (buffer-size))))
	(setq magic nil))

This seems to falsely assume that START is nil or a buffer position,
even though the docstring of `write-region' explicitly allows it to be a
string.

Best wishes,

     Gábor Braun


In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, cairo 
version 1.16.0)
 of 2021-03-28, modified by Debian built on x86-conova-01
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