GNU bug report logs - #30219
ert explainer for `equal' fails for equal-but-for-multibyte-ness strings

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

From: Philipp <p.stephani2 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.0.50; (should (equal ...)) bug for string equality
Date: Mon, 22 Jan 2018 23:55:13 +0100

Define the following ERT test:

(ert-deftest foo ()
  (should (equal "a\xFF" "a\u00FF")))

Then run M-x ert.  The test triggers an assertion.  This is because ERT
incorrectly assumes that two arrays are equal if their lengths and
elements are equal, but that's not the case when comparing unibyte and
multibyte strings.


In GNU Emacs 27.0.50 (build 10, x86_64-apple-darwin17.3.0, NS appkit-1561.20 Version 10.13.2 (Build 17C205))
 of 2018-01-22 built on p
Repository revision: 3558d96b60393893a346f4382b813ca0738f9d9b
Windowing system distributor 'Apple', version 10.3.1561
System Description:  Mac OS X 10.13.2

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --without-threads --with-modules --without-pop
 --with-mailutils --enable-gcc-warnings=yes --enable-checking
 --enable-check-lisp-object-type 'CFLAGS=-ggdb3 -O0''

Configured features:
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  locale-coding-system: utf-8-unix

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Message #14 received at 30219 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Philipp <p.stephani2 <at> gmail.com>
Cc: 30219 <at> debbugs.gnu.org
Subject: Re: bug#30219: 27.0.50; (should (equal ...)) bug for string equality
Date: Wed, 09 Oct 2019 23:29:15 +0200

Philipp <p.stephani2 <at> gmail.com> writes:

> Define the following ERT test:
>
> (ert-deftest foo ()
>   (should (equal "a\xFF" "a\u00FF")))
>
> Then run M-x ert.  The test triggers an assertion.  This is because ERT
> incorrectly assumes that two arrays are equal if their lengths and
> elements are equal, but that's not the case when comparing unibyte and
> multibyte strings.

I tried putting

(ert-deftest foo ()
  (should (equal "a\xFF" "a\u00FF")))

into one of the test files and I got

1 unexpected results:
   FAILED  foo

So I'm not able to reproduce this bug.  But the code in question hasn't
changed since this was reported, so I'm not sure why I can't reproduce
it.

Does anybody else see this?

      ((pred arrayp)
       (if (/= (length a) (length b))
           `(arrays-of-different-length ,(length a) ,(length b)
                                        ,a ,b
                                        ,@(unless (char-table-p a)
                                            `(first-mismatch-at
                                              ,(cl-mismatch a b :test 'equal))))
         (cl-loop for i from 0
                  for ai across a
                  for bi across b
                  for xi = (ert--explain-equal-rec ai bi)
                  do (when xi (cl-return `(array-elt ,i ,xi)))
                  finally (cl-assert (equal a b) t))))



-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #17 received at 30219 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: 30219 <at> debbugs.gnu.org
Cc: Lars Ingebrigtsen <larsi <at> gnus.org>, Philipp <p.stephani2 <at> gmail.com>
Subject: Re: bug#30219: 27.0.50; (should (equal ...)) bug for string equality
Date: Thu, 10 Oct 2019 16:34:03 +0200

The bug is directly reproducible, and not very surprising given the subtleties in mixed uni/multibyte string comparisons. ERT treats strings as arrays to be compared element-wise via `aref', which isn't how `equal' works.

There are several solutions, none perfect. I'll be back with a patch later today or tomorrow.

Message #20 received at 30219 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: 30219 <at> debbugs.gnu.org
Cc: Lars Ingebrigtsen <larsi <at> gnus.org>, Philipp <p.stephani2 <at> gmail.com>
Subject: Re: bug#30219: 27.0.50; (should (equal ...)) bug for string equality
Date: Thu, 10 Oct 2019 21:29:01 +0200

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

> There are several solutions, none perfect. I'll be back with a patch later today or tomorrow.

Please try this patch.

[0001-Correctly-explain-test-failures-with-mixed-uni-multi.patch (application/octet-stream, attachment)]

Message #23 received at 30219 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: 30219 <at> debbugs.gnu.org, Philipp <p.stephani2 <at> gmail.com>
Subject: Re: bug#30219: 27.0.50; (should (equal ...)) bug for string equality
Date: Fri, 11 Oct 2019 07:43:18 +0200

Mattias Engdegård <mattiase <at> acm.org> writes:

>        ((pred arrayp)
> +       ;; For mixed unibyte/multibyte string comparisons, make both multibyte.
> +       (when (and (stringp a)
> +                  (xor (multibyte-string-p a) (multibyte-string-p b)))
> +         (setq a (string-to-multibyte a))
> +         (setq b (string-to-multibyte b)))

I guess that makes sense.  We (possibly) lose text properties here, but
we don't care about those anyway in this context, I think?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #26 received at 30219 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 30219 <at> debbugs.gnu.org, Philipp <p.stephani2 <at> gmail.com>
Subject: Re: bug#30219: 27.0.50; (should (equal ...)) bug for string equality
Date: Fri, 11 Oct 2019 11:21:33 +0200

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

11 okt. 2019 kl. 07.43 skrev Lars Ingebrigtsen <larsi <at> gnus.org>:
> 
> I guess that makes sense.  We (possibly) lose text properties here, but
> we don't care about those anyway in this context, I think?

Oops, that wasn't intended. Second try.

[0001-Correctly-explain-test-failures-with-mixed-uni-multi.patch (application/octet-stream, attachment)]

Message #31 received at 30219 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: 30219 <at> debbugs.gnu.org, Philipp <p.stephani2 <at> gmail.com>
Subject: Re: bug#30219: 27.0.50; (should (equal ...)) bug for string equality
Date: Sun, 13 Oct 2019 20:10:11 +0200

Mattias Engdegård <mattiase <at> acm.org> writes:

>        ((pred arrayp)
> +       ;; For mixed unibyte/multibyte string comparisons, make both multibyte.
> +       (when (and (stringp a)
> +                  (xor (multibyte-string-p a) (multibyte-string-p b)))
> +         (setq a (string-to-multibyte a))
> +         (setq b (string-to-multibyte b)))

Looks good to me, I think.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #36 received at 30219-done <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 30219-done <at> debbugs.gnu.org, Philipp <p.stephani2 <at> gmail.com>
Subject: Re: bug#30219: 27.0.50; (should (equal ...)) bug for string equality
Date: Sun, 13 Oct 2019 20:30:52 +0200

13 okt. 2019 kl. 20.10 skrev Lars Ingebrigtsen <larsi <at> gnus.org>:
> 
> Looks good to me, I think.

Thank you, pushed to master and bug closed.

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