GNU bug report logs - #78378
[PATCH 0/2] home: services: Build "files" union allowing dangling symlinks.

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Message #29 received at 78378 <at> debbugs.gnu.org (full text, mbox):

From: Sergey Trofimov <sarg <at> sarg.org.ru>
To: Ludovic Courtès <ludo <at> gnu.org>
Cc: Hilton Chain <hako <at> ultrarare.space>,
 Janneke Nieuwenhuizen <janneke <at> gnu.org>,
 Tanguy Le Carrour <tanguy <at> bioneland.org>, 78378 <at> debbugs.gnu.org,
 Andrew Tropin <andrew <at> trop.in>
Subject: Re: [bug#78378] [PATCH 2/2] home: services: Build "files" union
 allowing dangling symlinks.
Date: Mon, 19 May 2025 12:00:30 +0200

Hi Ludovic
Ludovic Courtès <ludo <at> gnu.org> writes:

> Hi Sergey,
>
> Sergey Trofimov <sarg <at> sarg.org.ru> writes:
>
>> * gnu/home/services.scm (files->files-directory): Build file union
>> without checking for existence of included items.
>>
>> * tests/guix-home.sh: Verify symlinking files out of store works.
>>
>> Change-Id: I94054003f4a6be944252ce7a397cf56f0b979554
>
> [...]
>
>> @@ -343,7 +343,21 @@ (define (files->files-directory files)
>>    ;; leading to a build failure of "files.drv".
>>    (assert-no-duplicates files)
>>  
>> -  (file-union "files" files))
>> +  ;; Compute the file-union allowing dangling symlinks
>> +  ;; This enables creating symlinks to locations out of store
>> +  (computed-file
>> +   "files"
>> +   (with-imported-modules '((guix build utils))
>> +     #~(begin
>> +         (use-modules (guix build utils)
>> +                      (ice-9 match))
>> +         (mkdir #$output)
>> +         (chdir #$output)
>> +         (for-each (match-lambda
>> +                     ((target source)
>> +                      (mkdir-p (dirname target))
>> +                      (symlink source target)))
>> +                   '#$files)))))
>
> Instead of more or less duplicating ‘file-union’, how about adding a
> #:dangling-symlinks? argument to ‘file-union’ that would default to #f?
>
> When set to #t, the ‘stat’ call would not be emitted.
>
> That would reduce code duplication and make the intent clearer IMO.
>
> Ludo’.

I've applied your suggestion in v1.

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