This is a reland of commit 4bb05dc562
Initial commit didn't properly box the `void` return value, so when we
cast the return value to `ref #Top` to pass it to a Dart function (as
`Object?` or `dynamic`) it caused "illegal cast" traps.
In this commit we properly box the `externref` as `JSValue` (a proper
Dart class). A new test added passing the return value of a `void` JS
return to `print`.
Original change's description:
> [dart2wasm] Don't dartify JS values when returning as void
>
> When calling a JS function that returns `void`, avoid dartifying the
> result.
>
> Technically the return value of `void` functions can still be used, by
> casting the return type to `Object?` or `dynamic`. However this
> shouldn't be done, and `dartifyRaw` overhead just to support this case
> which should be extremely rare is too much.
>
> Any hacky code that uses return values of `void`-returning JS interop
> functions can manually dartify the retrun values with `toDart` or
> similar.
>
> Issue: https://github.com/dart-lang/sdk/issues/60357
> Change-Id: Ic370c7cf6eb6982f61f8a07c91e3bb93c5345ac6
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/417240
> Reviewed-by: Srujan Gaddam <srujzs@google.com>
> Reviewed-by: Martin Kustermann <kustermann@google.com>
> Commit-Queue: Ömer Ağacan <omersa@google.com>
Change-Id: I264211cca4f6b87e63d68909647975ab96f0b5bd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/421080
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Ömer Ağacan
b372b54ecb