Upgrade to Scala.js 1.20.1. #23884
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Upgrade to Scala.js 1.20.1. #23884
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sjrd
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This is a forward port of the compiler changes in the Scala.js commit scala-js/scala-js@5bfa254 It is now possible to use `@JSOperator` on a method named `**` in a JS type. In that case, it will translate to the JavaScript `**` operator. This is only valid when emitting ES 2016 or later, as it is not valid ES 2015 code. Without an explicit `@JSOperator` annotation, such a method still defaults to being a method call, to preserve backward compatibility.
In this commit, we ignore the new test for `linkTimeIf`.
This commit is a forward port of the compiler changes in scala-js/scala-js@5e842d8
When B <: A and C <: A, `linkTimeIf[A](cond) { B }{ C }` would
generate an `.asInstanceOf[A]` that casts the resulting value to a
supertype. However, this cast is redundant, as the linker will
prune one branch at link time, and the remaining expression is
already known to be a compatible type.
This commit eliminates the surrounding `.asInstanceOf` around the
`linkTimeIf[T]` when both `thenp` and `elsep` are known to be
subtypes of `T`. The optimizer already routinely performs this
optimization. However, that comes too late for the module instance
field alias analysis performed by `IncOptimizer`. In that case,
while the desugarer removes the `LinkTimeIf`, the extra
`AsInstanceOf` prevents aliasing the field. Removing the cast ahead
of time in the compiler allows field aliases to be recognized in
the presence of `LinkTimeIf`s.
This commit is a forward port of the Scala.js commit
scala-js/scala-js@9bb267c
We now recognize the shapes of varargs, deconstruct them, and emit instead calls to Scala.js-specific runtime methods. Those methods choose at link-time the best implementation for the target platform. The changes in `genActualArgs` revealed that we cannot trust `Symbol.isPrivate`. It uses `lastDenot.flagsUNSAFE` under the hood, which returns absurd results if `lastDenot` happened to be accessed within an `atPhase(...)` call. Therefore, we change those calls to `sym.is(Private)` instead. `Symbol.is` always uses an up-to-date denotation. Another consequence of the optimization is that the string representation of varargs seqs is altered in Scala.js. This is consistent with the Scala 2 behavior. We generalize the check file lookup of Vulpix to allow platform-dependent check files. We use that mechanism to introduce Scala.js-specific versions of the affected tests. This commit is essentially a forward port of the Scala.js commit scala-js/scala-js@24750cf except that, in dotc, previously we did not do the optimization at all.
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natsukagami
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Sep 10, 2025
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And related changes.
Scala.js 1.20.x contains the last IR changes required for good performance in WebAssembly. It would be really good to have this for the next LTS (and hence for 3.8.0), as it only applies to libraries recompiled with this new IR.