bug#30265: Fish shell has wrong path variables

[Ricardo Wurmus <rekado@elephly.net>]

Hi Meiyo,

thanks for the report.

> I am using GuixSD 0.14. After upgrading fish shell to latest version(v2.7.1) and
> running `guix gc`, fish shell does not work well.
[…]
> Fish shell is installed in:
> #+BEGIN_EXAMPLE
>   /gnu/store/ajbbi9cgj9j0my7v5habp0lcysaf2a51-fish-2.7.1/
> #+END_EXAMPLE
>
> But the environment variable $fish_function_path does not exist. And these
> environment variables point to non-existent paths:
> #+BEGIN_EXAMPLE
>   __fish_bin_dir /gnu/store/4jkxcz8kpy621ycmqn3rvs0fv6c98h6p-fish-2.7.1/bin
>   __fish_datadir /gnu/store/4jkxcz8kpy621ycmqn3rvs0fv6c98h6p-fish-2.7.1/share/fish
> #+END_EXAMPLE

Where are these environment variables defined?

> In conclusion, I think some path related variables are not set
> correctly when fish is compiled from source code and that caused the
> bug I met.

Some other packages record exact store references in cache files in the
user’s home directory.  As packages get upgraded and removed after
garbage collection, these references become invalid.

The question is whether these old store references are kept in files
outside of the store (and thus are not directly under our control), or
if the packages that Guix builds include incorrect references.  I guess
that it’s the former.

As is the case for these other programmes that record paths in cache
files, we would need to patch fish to record only the stable names of
links to those files (e.g. ~/.guix-profile/foo/bar) rather than the
actual file names in the store, which may disappear upon “guix gc”.

--
Ricardo

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