bug#57932: Mes has overly-generic MES_PREFIX search path (was: `environment_variables` in build containers are set wrong)

[Maxime Devos <maximedevos@telenet.be>]

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retitle 57392 Mes has overly-generic MES_PREFIX search path
thanks

On 19-09-2022 13:17, Ekaitz Zarraga wrote:
> Hi,
> 
> I have a package that depends on `mes`.
> 
> When I build it with `guix build $package -K` and I jump to the resulting build directory, the `environment_variables` file looks like this:
> 
> ```
> [...]
> export MES_PREFIX="/gnu/store/hy6abswwv4d89zp464fw52z65fkzr7h5-perl-5.34.0/"
> ```
> 
> The `MES_PREFIX` is set to Perl's installation directory, which is also the first element in `LIBRARY_PATH`.
> 
> If I change the order of the package inputs the order of the `LIBRARY_PATH` changes, which is not important, but the first element of `LIBRARY_PATH` is always the one in the `MES_PREFIX`. This doesn't look like the proper behavior: it should always be /gnu/store/*-mes-*

Looking at the search paths of 'mes', it has

            (search-path-specification
             (variable "MES_PREFIX")
             (separator #f)
             (files '("")))))

so it 'accept's _all_ the store items.  As such, I've renamed the issue 
(if you think the new name is inappropriate, feel free to rename it back.)

How about, instead of having a $MES_PREFIX environment variable and 
search path, substitute* uses of MES_PREFIX to #$output in a phase?

Greetings,
Maxime.

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