bug#70339: Constructing hg-fetch fixed-output derivation requires Mercurial

[Ludovic Courtès]

Hello!

Simon Tournier <zimon.toutoune@gmail.com> skribis:

> $ guix build -S -d hg-commitsigs
> substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
> 3,7 MB will be downloaded:
>   /gnu/store/6fya762sz5hjdj04vdn5g3v6zii6f11d-mercurial-6.2.2
> substituting /gnu/store/6fya762sz5hjdj04vdn5g3v6zii6f11d-mercurial-6.2.2...
> downloading from 
> https://ci.guix.gnu.org/nar/lzip/6fya762sz5hjdj04vdn5g3v6zii6f11d-mercurial-6.2.2
>  ...
>  mercurial-6.2.2  3.5MiB                                                   
> 529KiB/s 00:07 ▕██████████████████▏ 100.0%
>
> /gnu/store/pkb6zd9xfmxx6rsh4p7w3glh7xqg5sqy-hg-commitsigs-0.1.0-0.b53eb68-checkout.drv
>
>
> and it is unexpected.

That running ‘hg clone’ requires Mercurial isn’t totally unexpected to
me.  :-)

> I think it comes from this part:
>
>                      (hg-fetch '#$(hg-reference-url ref)
>                                '#$(hg-reference-changeset ref)
>                                #$output
>                                #:hg-command (string-append #+hg "/bin/hg")))
>
> from ’hg-fetch’ in (guix hg-download).  Here the #+hg is not required
> because just before there is:
>
>             (set-path-environment-variable "PATH" '("bin")
>                                            (match '#+inputs
>                                              (((names dirs outputs ...) ...)
>                                               dirs)))

Maybe, but one way or another, Mercurial is necessary.

Now, the ‘guix recover’ tool (or whatever you call it) you’re working on
could create a different fixed-output derivation producing the same
result but without using Mercurial; typically, the builder of that
derivation would download from SWH.

Does that make sense?

HTH,
Ludo’.