bug#30265: Fish shell has wrong path variables

[Meiyo Peng <meiyo.peng@gmail.com>]

Hi,

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.
#+BEGIN_EXAMPLE
  meiyo@guix ~$ fish
  fish:
  echo $_ " "; __fish_pwd
               ^
  in command substitution
          called on standard input

  fish:
  __fish_pwd
  ^
  in command substitution
          called on standard input

  in command substitution
          called on standard input

  fish:
  echo $_ " "; __fish_pwd
               ^
  in command substitution
          called on standard input
#+END_EXAMPLE

__fish_pwd is a fish function. It's defined in
`share/fish/functions/__fish_pwd.fish`.  The error message shows that fish
cannot load __fish_pwd's function definition from disk. After doing some
research, I found out that the error was caused by wrong environment variables.

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

Setting $fish_function_path to the correct path reduces the error message.
#+BEGIN_EXAMPLE
  set fish_function_path /gnu/store/ajbbi9cgj9j0my7v5habp0lcysaf2a51-fish-2.7.1/share/fish/functions
#+END_EXAMPLE

`share/fish/config.fish` states $__fish_datadir is set by fish.cpp,
and $fish_function_path is derived from $__fish_datadir.
#+BEGIN_SRC fish
  # __fish_datadir, __fish_sysconfdir, __fish_help_dir, __fish_bin_dir
  # are expected to have been set up by read_init from fish.cpp


  # Set up function and completion paths. Make sure that the fish
  # default functions/completions are included in the respective path.

  if not set -q fish_function_path
      set fish_function_path $configdir/fish/functions $__fish_sysconfdir/functions $__extra_functionsdir $__fish_datadir/functions
  end

  if not contains -- $__fish_datadir/functions $fish_function_path
      set fish_function_path $fish_function_path $__fish_datadir/functions
  end
#+END_SRC

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. But since I'm
not good at C++ programming, I will not dive deeper.

I hope that the information provided above is helpful.


Meiyo Peng