related to
- https://github.com/nushell/nushell/pull/9973
- https://github.com/nushell/nushell/pull/9918
thanks to @jntrnr and their super useful tips on this PR, i learned
about the parser + evaluation, so 🙏
# Description
because we already have `null` as the value of the type `nothing` and as
a followup to the two other attempts of mine, i propose to remove the
redundant `$nothing` built-in variable 😋
this PR is the first step, deprecating `$nothing`.
a followup PR will remove it altogether and wait for 0.87 👍⚙️ **details**: a new `NOTHING_VARIABLE_ID = 3` has been added,
parsing `$nothing` will create it, finally a `Value::Nothing` will be
produced and a warning will be reported.
this PR already fixes the `toolkit.nu` module so that it does not throw
a bunch of warnings each time 👌
# User-Facing Changes
`$nothing` is now deprecated and will be removed in 0.87
```nushell
> $nothing
Error: × Deprecated variable
╭─[entry #1:1:1]
1 │ $nothing
· ────┬───
· ╰── `$nothing` is deprecated and will be removed in 0.87.
╰────
help: Use `null` instead
```
# Tests + Formatting
tests have been updated, especially
- `nothing_fails_string`
- `nothing_fails_int`
which use a variable called `nil` now to make sure `nothing` does not
support cell paths 👍
# After Submitting
classic deprecation mention 👍
6c026242d4