[bug#36021] [PATCH] search-paths: 'environment-variable-definition' output for fish

[Meiyo Peng]

Hi Dan,

Dan Frumin writes:

> Some background on this patch:
> Right now whenever I do any Guix operation that requires me to modify
> environment variables (e.g. installing a Guile library requires me to update
> $GUILE_LOAD_PATH afterwards), Guix helpful tells me what commands I have to 
> run
> to update the variables.
>
> However, those commands are currently in bash/POSIX(?) format `export
> VAR=VALUE`. I've modified the `environment-variable-definition` function to
> support the syntax for Fish shell as well. I don't know if this method of
> looking at the $SHELL variable is sound, but it works  on my machine.
>
> Documentation for the `set' function in Fish: 
> https://fishshell.com/docs/current/commands.html#set
>
> PS: this is my first non-package patch for Guix so I apologize if there is 
> something wrong with the patch

I think this patch will cause more trouble than good.  Does this patch
replaces etc/profile with fish syntax script?  etc/profile is supposed
to be in POSIX shell syntax.  Fish shell has it's own configuration
files in /etc/fish/config.fish and /etc/fish/conf.d/*.fish.  If you
really want to generate fish syntax scripts, please put them in
/etc/fish/config.fish or /etc/fish/conf.d/*.fish.

See:
1. https://lists.gnu.org/archive/html/guix-devel/2019-01/msg00071.html
2. https://lists.gnu.org/archive/html/guix-devel/2019-01/msg00333.html
3. https://issues.guix.gnu.org/issue/34153

Have you tried the fish-foreign-env package?  You can source bash
scripts in fish via `fenv source ~/.guix-profile/etc/profile`.  That's how
the fish shell in Guix set up environment variables upon login.

Perhaps we can handle this better.  Do you have any suggestions?  My
idea:

1. The fish-foreign-env package is very useful but it's not installed by
default in order to avoid polluting user's profiles according to the
Guix convention.  In this case I think it's a useful utility rather than
pollution.  Do you want it to be installed together with the fish
package by default?

2. etc/profile is supposed to be sourced by a login shell.  And we
should avoid sourcing it from a non-login shell.  That's why I made the
fish package in Guix only sources it upon login.  That means starting a
new fish shell won't source it automatically.  So please source it
manually if you need the new environment variables (fenv source
~/.guix-profile/etc/profile).

3. We can write better documentations explaining how to deal with fish
shell in Guix.  There's an old discussion about having a Guix wiki or
a Guix book.


--
Meiyo Peng
https://www.pengmeiyu.com/