bug#63101: closed (30.0.50; nconc compiler optimization breaks user packages)

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Your message dated Thu, 27 Apr 2023 14:28:58 +0200
with message-id <E90776F9-3E5E-474A-B642-2F1043EFE1E0@acm.org>
and subject line Re: bug#63103: 30.0.50; nconc compiler optimization breaks 
user packages
has caused the debbugs.gnu.org bug report #63103,
regarding 30.0.50; nconc compiler optimization breaks user packages
to be marked as done.

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-- 
63103: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63103
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> --- Begin Message ---
>
>
>
> Subject: 
>
> 30.0.50; nconc compiler optimization breaks user packages
>
>
>
>
> Date: 
>
> Wed, 26 Apr 2023 18:57:29 +0300
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>
>
>
> 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. 
>
>
>
> --- End Message ---
> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#63103: 30.0.50; nconc compiler optimization breaks user packages
>
>
>
>
> Date: 
>
> Thu, 27 Apr 2023 14:28:58 +0200
>
>
>
>
> 27 apr. 2023 kl. 12.42 skrev Daniel Mendler <mail@daniel-mendler.de>:
>
> > I think it is
> > kind of nice that `nconc' can be used as a tool to turn a proper list
> > into an improper list and vice versa.
>
> It's a bit obscure, though --
>
>   (setcdr (last X) nil)
>
> is a lot clearer than
>
>   (nconc X nil)
>
> and when the latter is preferred for performance, a comment might be polite to 
> the reader.
>
> Anyway, a fix has been pushed to master, and the manual entry for `nconc` got 
> an extra example.
>
>
>
> --- End Message ---