^10.0.0-alpha.1 template literals output "regression"

[DZakh]

The compiler started adding empty strings around values in template literals. Technically doesn't break anything, but adds a redundant operation.

Example:

Js.log(`${1->Js.Int.toString}${2->Js.Int.toString}`)

Output:

console.log("" + (1).toString() + "" + (2).toString() + "");

Before:

console.log((1).toString() + (2).toString());

Context: DZakh/sury#1 (comment), #5514 (comment)

[cristianoc]

@DZakh see here: rescript-lang/syntax#602

[cristianoc]

That attempt at the syntax level is no good. Some cleanup is needed first. Then it should be doable in the compiler back-end.

[cristianoc]

It's actually not clear how to do it in the compiler back-end without invasive changes.
The code generated for normal (default "js") and "j" interpolation is the same: appending strings together.
In the back-end, one cannot distinguish them.
And only for "js" it is safe to remove "" + .
So we won't try to do this optimisation for this version of the compiler.

[DZakh]

What about the trailing empty string + ""?

[cristianoc]

Same

[cristianoc]

Putting this under milestone 10.1.

If anyone is interested in contributing a PR meanwhile, that's great.
That PR should be considered an optimisation, which should not fire for j`stuff` template expressions.