feat(builtin): add dump() for easy print-based debugging

[rami3l]

dbg!() is a very popular Rust std macro that can be used like so:

let a = 2;
let b = dbg!(a * 2) + 1;
//      ^-- prints: [src/main.rs:2:9] a * 2 = 4
assert_eq!(b, 5);

... note that a * 2 is not only printed for debugging but also passed on to the rest of the calculation, which makes it a perfect fit for inspecting complex evaluations such as those of chained method calls.

The idea of this PR is to mimic the behavior of that macro with what is currently available with MoonBit's compiler magic, i.e. loc~ : SourceLoc = _ and "%any.to_string".

The signature of this function dump() is as follows:

pub fn dump[T](t : T, name? : String, loc~ : SourceLoc = _) -> T 

... where the identifiers dump and name are taken from a similar Swift function.

[rami3l]

This function is marked as deprecated because it seems to be the only way to generate warnings with it. In Rust this logic is handled by clippy instead of rustc so there haven't been such concerns.

[coveralls]

Pull Request Test Coverage Report for Build 4053

Details

• 0 of 3 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 80.386%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
builtin/console.mbt	0	3	0.0%

Totals
Change from base Build 4047:	-0.04%
Covered Lines:	4377
Relevant Lines:	5445

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💛 - Coveralls

[bobzhang]

any_to_string is introduced for arbitrary code transformations where T is not sure if it satsifies Show. How is this different from dump[T:Show](...)
cc @Guest0x0 it makes sense to introduce support of ArgsRepr which is essentialy a stringified repr of args. so that we can do something like this:

pub fn dump[T:Show](t : T, name~ : ArgsRepr = _, loc~ : SourceLoc = _) -> T

[rami3l]

@bobzhang One thing that distinguishes Swift's dump() from Rust's dbg!() is that the former doesn't pose any restrictions on T whereas the latter depends on T: Debug (which is exclusively used for print-oriented pretty-printing, compensating for the lack of a built-in dumper in Rust) ¹.

I think the Show trait in MoonBit corresponds to the Display trait (which subsumes .to_string() in Rust) rather than Debug, so it makes more sense to add no bounds at all.

OTOH ArgsRepr will definitely be a nice addition.

Footnotes

1. The lack of distinction between Display and Debug seems like a common reason for which print-based debugging is less popular in traditional tech stacks; both approaches here allow the mitigation of this issue. ↩