Scoping is unintuitive

[pikajude]

$ ({ a }: with { a = "inner"; }; a) { a = "outer"; }
"outer"

Is this by design? It seems weird.

Contrarily, let a = "outer"; in let a = "inner"; in a returns "inner".

[vcunat]

This is by design IIRC because of some laziness-related properties. (I do agree it's counter-intuitive.)

Laziness above refers to evaluation and not the implementors ;-)

[shlevy]

This is by design. It makes most lookups in the presence of with much more efficient, and while I can see how it's a bit odd I think it's more often semantically what you actually want. At this point I don't think we can change it, given how much code depends on the current behavior.

[copumpkin]

😦 😦 😦

[bennofs]

Ah, so with never overrides the variables currently in scope? That could make building refactoring tools much easier, as it might actually be possible to know where an identifier comes from!

[shlevy]

Is there any action to do here?

[edolstra]

No, we can't change the with scoping rules at this point. And anyway, it would be a bad idea. See here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/with#Ambiguity_contra

[vcunat]

Well, that's more of an argument against having/using with at all. I always saw its main use as a shortener, but in a functional language on can instead do something like:

let lib = something.very.long; in { lib.foo /*etc..*/ } 

and do it without the scoping ambiguities.

Anyway, changing behavior of any currently valid code would need strong arguments.

[edolstra]

No, the Javascript example:

function f(foo, values) {
    with (foo) {
        console.log(values)
    }
}

is not a problem with Nix's scoping rules, because values always resolves to the same variable.

[vcunat]

Using with in a dynamic language may obscure where identifiers come from, regardless of using the nix ordering or the intuitive one. One could construct contrived examples, e.g. with two nested withs on attrsets passed by parameters where it isn't clear which of the two contains a certain identifier, etc.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/removing-most-uses-of-top-level-with/41233/1