Can't match a null (but can using the deprecated $nothing)

[NotTheDr01ds]

Describe the bug

match won't match a variable with null, but will match using $nothing (deprecated) as the pattern.

Ran into this in a real-world use-case that's a bit complex. Took me the better part of a day (on and off) to figure out the root cause and get it into some minimal reproducible examples. At the most basic:

How to reproduce

match $a {
    null => true,
    _ => false
}

Outputs false

Expected behavior

Outputs true

Additional context

Note that this MRE works if matching against $nothing, but this workaround will fail as of 0.87 when that is removed:

match $a {
    $nothing => true,
    _ => false
}

Returns true

Of course, the above is far oversimplified and would be better as an if statement (which does work):

if $a == null { true } else { false }

My real world use-case is that I have a calc involving two values. Consider it something like distancePerHour. My $hours variable may be:

• null
• 0
• Or a number (float or int)

If $hours is 0 or null, then I want the distancePerHour result to be null as well, since the source values are coming from a Nu table where I'll be inserting the distancePerHour results.

Consider:

def distancePerHour [ distance: any hours: any ] {
    match $hours {
        0 => null,
        null => null,
        _ => ( $distance / $hours )
    }
}

• distancePerHour 60 1 -> Works, returns 60
• distancePerHour 60 0 -> Works, returns null
• distancePerHour 60 null -> Fails with type mismatch for operator since the null didn't match and it fell through to the catch-all

(Side-note: As a workaround, yes, I could massage the data in advance, but that's not as "clean")

Keep in mind that the following works as expected (for now):

def distancePerHour [ distance: any hours: any ] {
    match $hours {
        0 => null,
        $nothing => null,
        _ => ( $distance / $hours )
    }
}

Another workaround (but, IMHO, clunky) would be to default the null to some "magic" value:

def distancePerHour [ distance: any hours: any ] {
    let hours = ($hours | default "nada")
    match $hours {
        0 => null,
        "nada" => null,
        _ => ( $distance / $hours )
    }
}

Of course, for this MRE, I could also default to 0, but that only works if the desired match result is the same for both 0 and null.

Screenshots

No response

Configuration

key	value
version	0.86.0
branch
commit_hash	5d8763e
build_os	linux-x86_64
build_target	x86_64-unknown-linux-gnu
rust_version	rustc 1.71.1 (eb26296b5 2023-08-03)
rust_channel	1.71.1-x86_64-unknown-linux-gnu
cargo_version	cargo 1.71.1 (7f1d04c00 2023-07-29)
build_time	2023-10-17 17:14:05 +00:00
build_rust_channel	release
allocator	mimalloc
features	dataframe, default, extra, sqlite, static-link-openssl, trash, which, zip
installed_plugins

[amtoine]

not sure it's in our issue tracker already but i'm quite sure i've seen that somewhere, good catch 🙏