GNU bug report logs - #26317
26.0.50; Small incompatibility in ibuffer.el (ibuffer-compile-format)

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: John Mastro <john.b.mastro <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.0.50; Small incompatibility in ibuffer.el (ibuffer-compile-format)
Date: Thu, 30 Mar 2017 16:07:59 -0700

In commit 7e2a8b1, ibuffer.el was change to use `string-width' in a couple
places where it previously used `length'. The result is that custom columns
which can return nil, which worked in Emacs 25, will now cause an error.

To reproduce, run `emacs -Q', yank the following into *scratch*, and evaluate
it:

    (require 'ibuffer)

    (define-ibuffer-column my-column
      (:name "X")
      (and (equal (buffer-name) "*scratch*") "Y"))

    (setq ibuffer-formats '((mark modified read-only
                                  " " (name 18 18 :left :elide)
                                  " " (my-column 5 5 :left)
                                  " " filename-and-process)))

    (ibuffer)

It works in Emacs 25, but in Emacs 26 an error is signaled:

    Debugger entered--Lisp error: (wrong-type-argument stringp nil)
      string-width(nil)

I came across this because I use the `ibuffer-vc' package, which defines a
column (`vc-status') whose implementation returns nil for some buffers (by
default, non-file-visiting buffers and buffers visiting remote files).

I will follow up with a patch in a separate email (so I can include the bug
number in the commit message).

        John

Message #8 received at 26317 <at> debbugs.gnu.org (full text, mbox):

From: John Mastro <john.b.mastro <at> gmail.com>
To: 26317 <at> debbugs.gnu.org
Subject: Re: bug#26317: 26.0.50;
 Small incompatibility in ibuffer.el (ibuffer-compile-format)
Date: Thu, 30 Mar 2017 16:15:16 -0700

[Message part 1 (text/plain, inline)]

John Mastro <john.b.mastro <at> gmail.com> wrote:
> In commit 7e2a8b1, ibuffer.el was change to use `string-width' in a couple
> places where it previously used `length'. The result is that custom columns
> which can return nil, which worked in Emacs 25, will now cause an error.

I've attached a patch that fixes this. Rather than touching the calls to
`string-width' directly, it translates nil to the empty string. Either
way restores compatibility with Emacs 25, but translating nil to the
empty string seems preferable in that it saves later code from caring.

Even though it's a tiny change, I'm not a regular contributor or
particularly familiar with ibuffer's implementation, so any review is
appreciated. My copyright assignment is on file.

        John

[0001-Fix-a-small-incompatibility-in-ibuffer.patch (application/octet-stream, attachment)]

Message #13 received at 26317-done <at> debbugs.gnu.org (full text, mbox):

From: Mark Oteiza <mvoteiza <at> udel.edu>
To: John Mastro <john.b.mastro <at> gmail.com>
Cc: 26317-done <at> debbugs.gnu.org
Subject: Re: bug#26317: 26.0.50;
 Small incompatibility in ibuffer.el (ibuffer-compile-format)
Date: Thu, 30 Mar 2017 20:25:06 -0400

John Mastro <john.b.mastro <at> gmail.com> writes:

> John Mastro <john.b.mastro <at> gmail.com> wrote:
>> In commit 7e2a8b1, ibuffer.el was change to use `string-width' in a couple
>> places where it previously used `length'. The result is that custom columns
>> which can return nil, which worked in Emacs 25, will now cause an error.
>
> I've attached a patch that fixes this. Rather than touching the calls to
> `string-width' directly, it translates nil to the empty string. Either
> way restores compatibility with Emacs 25, but translating nil to the
> empty string seems preferable in that it saves later code from caring.
>
> Even though it's a tiny change, I'm not a regular contributor or
> particularly familiar with ibuffer's implementation, so any review is
> appreciated. My copyright assignment is on file.

LGTM.  Sorry for breaking it, and thanks for the fix!

Applied as eeaa707.

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