Previously in a0505f52d9
the profile script was modified to preserve XDG_DATA_DIRS.
This had the side-effect of making the script not idempotent,
adding duplicate entries for every installation every time it's sourced.
On my current system that results in this value:
/home/mkhl/.local/share/flatpak/exports/share /var/lib/flatpak/exports/share /home/mkhl/.local/share/flatpak/exports/share /var/lib/flatpak/exports/share /usr/local/share /usr/share
which in turn has the side-effect of the GNOME search settings showing two entries
for every application installed via flatpak.
This change makes the script check that an entry is new before adding it.
It also uses `set -p` (short for `--prepend`) to add them.
N.B.
`set -p VAR val` is equivalent to `set VAR val $VAR`
`$var[-1..1]` reverses the order of elements
so after iterating the first element of `$installations`
becomes the first element of `$XDG_DATA_DIRS`
The profile script previously nuked `XDG_DATA_DIRS` and then
“helpfully” re-populated it with FHS paths. This was especially
bad for systems like NixOS, which do not have `/usr`
and rely on `XDG_DATA_DIRS` heavily.
Quoting from https://fishshell.com/docs/current/cmds/set.html
> If a variable is set to zero elements, it will become a list with zero elements.
And indeed, that is what the `set -x --path XDG_DATA_DIRS` command does.
We need to list the value explicitly, if we want to preserve it
while setting variable options.
Technically, Fish users can already make this work using
https://github.com/edc/bass, but it's also nice to have this working on
an out-of-the-box Flatpak installation.
Fixes#3109.
Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>
