This renames abbreviation triggers from `--trigger-on entry` and
`--trigger-on exec` to `--on-space` and `--on-enter`. These names are less
precise, as abbreviations trigger on any character that terminates a word
or any key binding that triggers exec, but they're also more human friendly
and that's a better tradeoff.
This adds support for the `--function` option of abbreviations, so that the
expansion of an abbreviation may be generated dynamically via a fish
function.
Prior to this change, abbreviations were stored as fish variables, often
universal. However we intend to add additional features to abbreviations
which would be very awkward to shoe-horn into variables.
Re-implement abbreviations using a builtin, managing them internally.
Existing abbreviations stored in universal variables are still imported,
for compatibility. However new abbreviations will need to be added to a
function. A follow-up commit will add it.
Now that abbr is a built-in, remove the abbr function; but leave the
abbr.fish file so that stale files from past installs do not override
the abbr builtin.
This was supposed to act like `type -q` or `command -q`, in that it
returns 0 if at least 1 exists.
But because it used the wrong variable it didn't.
Fixes#8431.
