bug#59256: Emacs-guix tab-completion returns gexp error

[Joshua Hecker via Bug reports for GNU Guix <bug-guix@gnu.org>]

Maxime Devos <maximedevos@telenet.be> writes:

Sorry for getting back to you so late, life got in the way, work and
setting up my POWER9 machine :). But I still hope you can provide some
wisdom.

> I've heard about something about Guile sockets and REPLs, so I've
> investigated a bit and I think I found a Guix bug instead of a Guile
> bug (and is unrelated to sockets or REPLs):

Im glad you found something different happening behind the scenes. I
only came to that conclusion because I loaded my own [default] geiser
repl with emacs-guix mode, and comparing that to the emacs-guix repl
that loads automatically.

> In the error message, there is a mention of "#~". Perhaps somehow, no
> hash extension (not sure about terminology) for G-exps installed?
> This is confirmed by:
>
> scheme@(emacs-guix) [2]> (fluid-ref* %read-hash-procedures 0)
> $24 = ((#\. . #<procedure 7fbac9e323d0 at ice-9/boot-9.scm:2251:18 (c
> port)>))
>
> It's also not a matter of some parametrisation:
>
> scheme@(emacs-guix) [2]> (fluid-ref* %read-hash-procedures 1)
> $25 = ()
> scheme@(emacs-guix) [2]> (fluid-ref* %read-hash-procedures 2)
> $26 = ()
>
> How does this happen? (after all, (guix scripts deploy) imports (guix gexp))
>
> Going by the backtrace I get:
>
> [...]
> In guix/ui.scm:
>    2263:7 17 (run-guix . _)
> In ice-9/boot-9.scm:
>   1747:15 16 (with-exception-handler #<procedure 7fbac4ead6c0 at
>   ice-9/boot-9.scm:1831:7 (exn)> _ #:unwind? _ #:unwind-for-type _)
> In guix/ui.scm:
>   2184:20 15 (show-guix-help)
> In srfi/srfi-1.scm:
>    691:23 14 (filter-map #<procedure source-file-command (file)> _ . _)
> In ice-9/ports.scm:
>    433:17 13 (call-with-input-file _ _ #:binary _ #:encoding _
>    #:guess-encoding _)
> In guix/ui.scm:
>   2109:16 12 (_ #<input:
>   /home/antipode/.config/guix/current/share/guile/site/3.0/guix/scripts/deploy.scm
>   22>)
> In ice-9/read.scm:
>    734:20 11 (%read #<input:
>    /home/antipode/.config/guix/current/share/guile/site/3.0/guix/scripts/deploy.scm
>    22> #<procedure 7fbac42c5280 at ice-9/read.scm:862:8 (line column
>   datum)> _)
>     210:5 10 (read-parenthesized #\))
> [...]
>
> That is, one of the earliest things that happen, is that (guix ui)
> reads the file "(guix scripts deploy)" -- it doesn't do the reflection
> equivalent of (use-module ...) which will run the imports before
> reading the rest of the code.
>
> As such, the hash extension isn't installed even though it is required
> to read the file and even though the required module (guix gexp) is
> listed in the imports!
>
> To fix this, I propose modifying 'source-file-command' in (guix ui),
> by adding a clause to
>
>         (match (read port)
>           (('define-command _ ('synopsis synopsis)
>              _ ...)
>            (command command-name synopsis 'main))
>           (('define-command _
>              ('category category) ('synopsis synopsis)
>              _ ...)
>            (command command-name synopsis category))
>           ((? eof-object?)
>            #f)
>           (_
>            (loop)))))))
>
> which recognises (define-module [...] #:use-module MODULE ...),
> and if MODULE is (guix gexp) or (srfi srfi-88), then does
> (resolve-module 'MODULE #:ensure #false) before continuing with
> (loop).
>
> (Untested!)

Very cool that you found this. I would love to test this out, is there
any formal way to apply this and have emacs point to the test guix?
Sorry for novice questions, any info to do the work would be much appreciated.

Stay safe,
-Joshua