[bug#53676] [PATCH 4/5] services: pulseaudio: Add an extra-script-files configuration field.

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Hi Maxim,

Am Sonntag, dem 06.02.2022 um 02:25 -0500 schrieb Maxim Cournoyer:
> Hi Liliana,
> 
> [...]
> 
> > > 'strip-store-file-name' would be able to get the name from the
> > > store
> > > item (built derivation), but file-union takes a "two-element list
> > > where the first element is the file name to use in the new
> > > directory,
> > > and the second element is a gexp denoting the target file", e.g.,
> > > before the file-like object is built.  I don't see an easy way to
> > > make it work.
> > For the record, I do think we'd like to use file-like objects here,
> > not
> > raw gexps.  If that fails, why not expose the name to gexp mapping
> > completely?  I don't know why you'd want to take away that control.
> 
> If we limit ourselves to file-like objects, we can do something like
> this:
> 
> --8<---------------cut here---------------start------------->8---
> 1 file changed, 20 insertions(+), 4 deletions(-)
> gnu/services/sound.scm | 24 ++++++++++++++++++++----
> 
> modified   gnu/services/sound.scm
> @@ -26,10 +26,12 @@ (define-module (gnu services sound)
>    #:use-module (gnu services)
>    #:use-module (gnu system pam)
>    #:use-module (gnu system shadow)
> +  #:use-module (guix diagnostics)
>    #:use-module (guix gexp)
>    #:use-module (guix packages)
>    #:use-module (guix records)
>    #:use-module (guix store)
> +  #:use-module (guix ui)
>    #:use-module (gnu packages audio)
>    #:use-module (gnu packages linux)
>    #:use-module (gnu packages pulseaudio)
> @@ -149,10 +151,24 @@ (define pulseaudio-environment
>         ("PULSE_CLIENTCONFIG" . "/etc/pulse/client.conf")))))
>  
>  (define (extra-script-files->file-union extra-script-files)
> -  "Return a G-exp obtained by processing EXTRA-SCRIPT-FILES with FILE-
> UNION.
> -Each file is named \"snippet-n.pa\", where N is their 1-offset index."
> -  (let ((labels (map (lambda (n) (format #f "snippet-~a.pa" n))
> -                     (iota (length extra-script-files) 1))))
> +  "Return a G-exp obtained by processing EXTRA-SCRIPT-FILES with FILE-
> UNION."
> +
> +  (define (file-like->name file)
> +    (let ((name (match file
> +                  ((? local-file?)
> +                   (local-file-name file))
> +                  ((? plain-file?)
> +                   (plain-file-name file))
> +                  ((? computed-file?)
> +                   (computed-file-name file))
> +                  (_ (leave (G_ "~a is not a local-file, plain-file or
> \
> +computed-file object~%") file)))))
> +      (unless (string-suffix? name ".pa")
> +        (leave (G_ "`~a' lacks the required '.pa' file name
> extension~%")
> +               name))
> +      name))
> +
> +  (let ((labels (map file-like->name extra-script-files)))
>      (file-union "default.pa.d" (zip labels extra-script-files))))
>  
>  (define pulseaudio-etc
> --8<---------------cut here---------------end--------------->8---
> 
> It works; and I agree it's nice to have control over the file name.
Note that file-like->name serves multiple duties here.  In my opinion
it'd be better to

--8<---------------cut here---------------start------------->8---
(define (file-like-name file)
  ((match file
     ((? local-file?) local-file-name)
     ((? plain-file?) plain-file-name)
     ((? computed-file?) computed-file-name)
     [...]
     (_ (const #f))) ; alternatively raise an error
   file))
--8<---------------cut here---------------end--------------->8---
That at least decouples it from the burden of having to check whether
it is a valid pulseaudio script file name, which makes it reusable
elsewhere.  As a note regarding correctness, perhaps we should write an
implementation in (guix gexp) that works for everything that has a
gexp-compiler, but that's out of scope for now.

On the pulseaudio side, you'd compose that with an
--8<---------------cut here---------------start------------->8---
(define (assert-pulseaudio-script-file-name name)
  (unless name (raise ...))
  (unless (string-suffix? name ".pa") (leave ...))
  name)
--8<---------------cut here---------------end--------------->8---

Cheers