bug#71270: 30.0.50; Execute dired-do-shell-command will encounter 'wrong-type-argument stringp nil' error

bug#71270: 30.0.50; Execute dired-do-shell-command will encounter 'wrong-type-argument stringp nil' error

[Yuwei Tian]

After commit 74f15ad72d937b309dafecba872bccd1a880181e, it will
encounter 'wrong-type-argument string nil' error when executing
dired-do-shell-command.

Here is the backtrace:

  string-match("/" nil 0)
  split-string(nil "/")
  xdg-mime-apps(nil)
  shell-command-guess-xdg(nil ("xxxxxxx"))

The shell-command-guess-xdg is being called in the chain of
shell-command-guess-functions. Here is the definition of
shell-command-guess-xdg function:

(defun shell-command-guess-xdg (commands files)
  "Populate COMMANDS by XDG configuration for FILES."
  (require 'xdg)
  (let* ((xdg-mime (when (executable-find "xdg-mime")
                     (string-trim-right
                      (shell-command-to-string
                       (concat "xdg-mime query filetype "
                               (shell-quote-argument (car files)))))))
         (xdg-mime-apps (unless (string-empty-p xdg-mime)
                          (xdg-mime-apps xdg-mime)))
         (xdg-commands
          (mapcar (lambda (desktop)
                    (setq desktop (xdg-desktop-read-file desktop))
                    (propertize
                     (replace-regexp-in-string
                      " .*" "" (gethash "Exec" desktop))
                     'name (gethash "Name" desktop)))
                  xdg-mime-apps)))
    (append xdg-commands commands)))

xdg-mime will be nil if xdg-mime not found, string-empty-p returns
nil and xdg-mime-apps will be called with nil.


In GNU Emacs 30.0.50 (build 1, x86_64-apple-darwin23.5.0, NS
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fishtai0-mac.local
Windowing system distributor 'Apple', version 10.3.2487
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bug#71270: 30.0.50; Execute dired-do-shell-command will encounter 'wrong-type-argument stringp nil' error

[Juri Linkov]

close 71270 30.0.50
thanks

> After commit 74f15ad72d937b309dafecba872bccd1a880181e, it will
> encounter 'wrong-type-argument string nil' error when executing
> dired-do-shell-command.
>
> Here is the backtrace:
>
>   string-match("/" nil 0)
>   split-string(nil "/")
>   xdg-mime-apps(nil)
>   shell-command-guess-xdg(nil ("xxxxxxx"))
>
> The shell-command-guess-xdg is being called in the chain of
> shell-command-guess-functions. Here is the definition of
> shell-command-guess-xdg function:

Thanks for the detailed analysis.

> xdg-mime will be nil if xdg-mime not found, string-empty-p returns
> nil and xdg-mime-apps will be called with nil.

I didn't expect that string-empty-p returns nil for nil
(maybe because I'm accustomed to programming languages
where "" and nil both are empty):

  (string-empty-p "")  => t
  (string-empty-p nil) => nil

So now I added the explicit check for the nil value, and pushed the fix.

bug#71270: 30.0.50; Execute dired-do-shell-command will encounter 'wrong-type-argument stringp nil' error

[Eli Zaretskii]

> From: Yuwei Tian <fishtai0@gmail.com>
> Date: Thu, 30 May 2024 14:24:35 +0800
> 
> After commit 74f15ad72d937b309dafecba872bccd1a880181e, it will
> encounter 'wrong-type-argument string nil' error when executing
> dired-do-shell-command.
> 
> Here is the backtrace:
> 
>   string-match("/" nil 0)
>   split-string(nil "/")
>   xdg-mime-apps(nil)
>   shell-command-guess-xdg(nil ("xxxxxxx"))
> 
> The shell-command-guess-xdg is being called in the chain of
> shell-command-guess-functions. Here is the definition of
> shell-command-guess-xdg function:
> 
> (defun shell-command-guess-xdg (commands files)
>   "Populate COMMANDS by XDG configuration for FILES."
>   (require 'xdg)
>   (let* ((xdg-mime (when (executable-find "xdg-mime")
>                      (string-trim-right
>                       (shell-command-to-string
>                        (concat "xdg-mime query filetype "
>                                (shell-quote-argument (car files)))))))
>          (xdg-mime-apps (unless (string-empty-p xdg-mime)
>                           (xdg-mime-apps xdg-mime)))
>          (xdg-commands
>           (mapcar (lambda (desktop)
>                     (setq desktop (xdg-desktop-read-file desktop))
>                     (propertize
>                      (replace-regexp-in-string
>                       " .*" "" (gethash "Exec" desktop))
>                      'name (gethash "Name" desktop)))
>                   xdg-mime-apps)))
>     (append xdg-commands commands)))
> 
> xdg-mime will be nil if xdg-mime not found, string-empty-p returns
> nil and xdg-mime-apps will be called with nil.

Thanks, I'm adding Juri to this discussion.