This was intended to stop showing the user "unimportant" variables,
but it just didn't complete them entirely, even if the current token
starts with a dunder (or `fish` of all things!).
Because completions sort `_` last, let's just complete these always
and let the user filter them.
Add missing options:
--path causes the specified variable to be treated as a path variable, meaning it will automatically be split on colons, and joined using colons when quoted (echo "$PATH") or exported.
--unpath causes the specified variable to not be treated as a path variable. Variables with a name ending in "PATH" are automatically path variables, so this can be used to treat such a variable normally.
[ci skip]
On `set fish_color_cwd <TAB>`, a bunch of named colors are
shown in the pager. Each and every one has a description of "Color".
These are all very obviously colors, and none are not colors,
the description does not tell us anything specific about the item.
Descriptions in situations like this are actually a hinderance
because of the way they cause less to fit into the pager. Remove it
Now the description includes the variable scope, `set [-e] -[Ugl]`
completions only provide variables matching that scope, and completions
that shouldn't be modified are hidden from the user. Completions that
are often modified but rarely unset (`fish_*` variables) are omitted
from `set -e` completions.
A new helper function `__fish_seen_argument` has been added that makes
it easy to only provied completions for a specific flag.
