GNU bug report logs - #63101
30.0.50; nconc compiler optimization breaks user packages

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Package: emacs;

Reported by: Maks <mvproton <at> gmail.com>

Date: Thu, 27 Apr 2023 04:17:03 UTC

Severity: normal

Merged with 63100, 63103

Found in version 30.0.50

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

Bug is archived. No further changes may be made.

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Report forwarded to bug-gnu-emacs <at> gnu.org:
bug#63101; Package emacs. (Thu, 27 Apr 2023 04:17:03 GMT) Full text and rfc822 format available.
Acknowledgement sent to Maks <mvproton <at> gmail.com>:
New bug report received and forwarded. Copy sent to bug-gnu-emacs <at> gnu.org. (Thu, 27 Apr 2023 04:17:03 GMT) Full text and rfc822 format available.

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

From: Maks <mvproton <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.0.50; nconc compiler optimization breaks user packages
Date: Wed, 26 Apr 2023 18:57:29 +0300

Hello,

after long debugging time I figured out that commit
e6ca5834a6eab91023e9f968b65683d0a74db1e7 ('Improved nconc and append
compiler optimisations') breaks package vertico.el. I'm not completely
understanding how it works but try to describe the problem.

If I set breakpoint before breaking commit I get the following stacktrace:

```
Debugger entered--entering a function:
* vertico--affixate((#("report-emacs-bug" 0 1 (face (completions-first-difference))) #("cd" 0 1 (face (completions-first-difference))) #("5x5" 0 1 (face (completions-first-difference))) #("arp" 0 1 (face (completions-first-difference))) #("dbx" 0 1 (face (completions-first-difference))) #("dig" 0 1 (face (completions-first-difference))) #("erc" 0 1 (face (completions-first-difference))) #("ert" 0 1 (face (completions-first-difference))) #("eww" 0 1 (face (completions-first-difference))) #("ftp" 0 1 (face (completions-first-difference)))))
  vertico--arrange-candidates()
  vertico--exhibit()
```
, but after breaking commit I get slightly different stacktrace:

```
Debugger entered--entering a function:
* vertico--affixate((#("report-emacs-bug" 0 1 (face (completions-first-difference))) #("cd" 0 1 (face (completions-first-difference))) #("5x5" 0 1 (face (completions-first-difference))) #("arp" 0 1 (face (completions-first-difference))) #("dbx" 0 1 (face (completions-first-difference))) #("dig" 0 1 (face (completions-first-difference))) #("erc" 0 1 (face (completions-first-difference))) #("ert" 0 1 (face (completions-first-difference))) #("eww" 0 1 (face (completions-first-difference))) #("ftp" 0 1 (face (completions-first-difference))) . 0))
  vertico--arrange-candidates()
  vertico--exhibit()
```

As you can see, the difference is in the tail of the input list. This
list comes from completion-hilit-commonality function from
minibuffer.el and it has nconc call. But testing
completion-hilit-commonality in REPL separetely from vertico.el package
give the same result (with 0 at the end of list).

Before sending this report I have tried a lot of versions of the
vertico.el package and have the same result. So I tend to think that problem is not directly
related to package.
Merged 63100 63101 63103. Request was from Eli Zaretskii <eliz <at> gnu.org> to control <at> debbugs.gnu.org. (Thu, 27 Apr 2023 05:48:02 GMT) Full text and rfc822 format available.
bug archived. Request was from Debbugs Internal Request <help-debbugs <at> gnu.org> to internal_control <at> debbugs.gnu.org. (Fri, 26 May 2023 11:24:05 GMT) Full text and rfc822 format available.
This bug report was last modified 2 years and 86 days ago.

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