Throw Js Erros constructor EvalError, RangeError, etc

[aspeddro]

After #6611 was merged it is no longer possible to throw errors like EvalError. The throw statement now is thow new Error(exn).

Example: The Js.Exn.raiseEvalError function:

rescript-compiler/jscomp/others/js_exn.res

Line 48 in 0b1443f

let raiseEvalError = str => raise((Obj.magic((makeEvalError(str): eval_error)): exn))

compile to:

rescript-compiler/lib/es6/js_exn.js

Lines 10 to 14 in 0b1443f

	function raiseEvalError(str) {
	throw new Error(new EvalError(str).RE_EXN_ID, {
	cause: new EvalError(str)
	});
	}

This PR add a function throw:

let throw: exn => 'a = %raw("function (exn) {
  throw exn;
}")

Side question

Here a question arises whether we should support EvalError and others, or encourage ReScript exceptions. Recently documented the exceptions builtin (rescript-lang/rescript-lang.org#880)

My idea is to use ReScript exceptions and not bindings to Js Error (i.e @new external make: string => t = "Error"). We will still catch Js Errors

Related #6929

[DZakh]

This change will break my libs and applications

[aspeddro]

Your libs use Js.Exn.{raiseEvalError,raiseRangeError} functions?

[DZakh]

Sorry, I've taken a look at your PR, and it indeed improves things compared to the current v12 alpha release. But it doesn't solve the root of the problem, and for example, the Js.Exn.raiseError still have a regressed behaviour compared to v11.

I'm working on the PR #6933, which should automatically fix the issue you're trying to solve in the PR. This is why I think it's not needed.

[aspeddro]

What is the regression compared to v11?

[DZakh]

What is the regression compared to v11?

Previously it would throw a new Error with the message provided via the arguments. Now it throws new Error("Failure", ... where message is hidden in the cause.

The main usecase for the Js.Exn.raiseError was to throw an error with a readable error message, which would be displayed nicely in logs, but now it's hidden in the cause field

[DZakh]

And if we are talking about the issue #6929
Your PR will fix the case with Js.Exn.raiseError, but for the following code it still won't work: https://rescript-lang.org/try?version=v12.0.0-alpha.1&code=C4JwngBA3gUBEFIQEMDuAKABu9BKAvAHxTAAWIA9qhAK4B2AJgKYBmAlnUwwL656a4Y3CAGNkwEaWgwAPhCYAPOhCIQUbAM5N0iuoO4wgA