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Wasm-friendly implementation of varargs. #5215

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3215203
Wasm-friendly implementation of varargs.
sjrd Jul 26, 2025
960d7eb
Squash: Put the toXVarArgs methods in scala.scalajs.runtime.*.
sjrd Aug 4, 2025
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101 changes: 57 additions & 44 deletions compiler/src/main/scala/org/scalajs/nscplugin/GenJSCode.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -5914,10 +5914,26 @@ abstract class GenJSCode[G <: Global with Singleton](val global: G)
*/
for ((arg, wasRepeated) <- args.zipAll(wereRepeated, EmptyTree, false)) yield {
if (wasRepeated) {
tryGenRepeatedParamAsJSArray(arg, handleNil = false).fold {
genExpr(arg)
} { genArgs =>
genJSArrayToVarArgs(js.JSArrayConstr(genArgs))
/* If the argument is a call to the compiler's chosen `wrapArray`
* method with an array literal as argument, we know it actually
* came from expanded varargs. In that case, rewrite to calling our
* custom `scala.scalajs.runtime.to*VarArgs` method. These methods
* choose the best implementation of varargs depending on the
* target platform.
*/
arg match {
case MaybeAsInstanceOf(wrapArray @ WrapArray(
MaybeAsInstanceOf(arrayValue: ArrayValue))) =>
implicit val pos = wrapArray.pos
js.Apply(
js.ApplyFlags.empty,
genLoadModule(RuntimePackageModule),
js.MethodIdent(WrapArray.wrapArraySymToToVarArgsName(wrapArray.symbol)),
List(genExpr(arrayValue))
)(jstpe.ClassType(encodeClassName(SeqClass), nullable = true))

case _ =>
genExpr(arg)
}
} else {
genExpr(arg)
Expand Down Expand Up @@ -6069,27 +6085,6 @@ abstract class GenJSCode[G <: Global with Singleton](val global: G)
* Otherwise, it returns a JSSpread with the Seq converted to a js.Array.
*/
private def genPrimitiveJSRepeatedParam(arg: Tree): List[js.TreeOrJSSpread] = {
tryGenRepeatedParamAsJSArray(arg, handleNil = true) getOrElse {
/* Fall back to calling runtime.toJSVarArgs to perform the conversion
* to js.Array, then wrap in a Spread operator.
*/
implicit val pos = arg.pos
val jsArrayArg = genApplyMethod(
genLoadModule(RuntimePackageModule),
Runtime_toJSVarArgs,
List(genExpr(arg)))
List(js.JSSpread(jsArrayArg))
}
}

/** Try and expand a repeated param (xs: T*) at compile-time.
* This method recognizes the shapes of tree generated by the desugaring
* of repeated params in Scala, and expands them.
* If `arg` does not have the shape of a generated repeated param, this
* method returns `None`.
*/
private def tryGenRepeatedParamAsJSArray(arg: Tree,
handleNil: Boolean): Option[List[js.Tree]] = {
implicit val pos = arg.pos

// Given a method `def foo(args: T*)`
Expand All @@ -6101,15 +6096,22 @@ abstract class GenJSCode[G <: Global with Singleton](val global: G)
* the type before erasure.
*/
val elemTpe = tpt.tpe
Some(elems.map(e => ensureBoxed(genExpr(e), elemTpe)))
elems.map(e => ensureBoxed(genExpr(e), elemTpe))

// foo()
case Select(_, _) if handleNil && arg.symbol == NilModule =>
Some(Nil)
case Select(_, _) if arg.symbol == NilModule =>
Nil

// foo(argSeq:_*) - cannot be optimized
case _ =>
None
/* Fall back to calling runtime.toJSVarArgs to perform the conversion
* to js.Array, then wrap in a Spread operator.
*/
val jsArrayArg = genApplyMethod(
genLoadModule(RuntimePackageModule),
Runtime_toJSVarArgs,
List(genExpr(arg)))
List(js.JSSpread(jsArrayArg))
}
}

Expand Down Expand Up @@ -6137,25 +6139,36 @@ abstract class GenJSCode[G <: Global with Singleton](val global: G)
def isClassTagBasedWrapArrayMethod(sym: Symbol): Boolean =
sym == wrapRefArrayMethod || sym == genericWrapArrayMethod

private val isWrapArray: Set[Symbol] = {
Seq(
nme.wrapRefArray,
nme.wrapByteArray,
nme.wrapShortArray,
nme.wrapCharArray,
nme.wrapIntArray,
nme.wrapLongArray,
nme.wrapFloatArray,
nme.wrapDoubleArray,
nme.wrapBooleanArray,
nme.wrapUnitArray,
nme.genericWrapArray
).map(getMemberMethod(wrapArrayModule, _)).toSet
val wrapArraySymToToVarArgsName: Map[Symbol, MethodName] = {
val SeqClassRef = jstpe.ClassRef(encodeClassName(SeqClass))

def make(simpleName: String, argTypeRef: jstpe.TypeRef): MethodName =
MethodName(simpleName, argTypeRef :: Nil, SeqClassRef)

val items: Seq[(Name, String, jstpe.TypeRef)] = Seq(
(nme.genericWrapArray, "toGenericVarArgs", jswkn.ObjectRef),
(nme.wrapRefArray, "toRefVarArgs", jstpe.ArrayTypeRef(jswkn.ObjectRef, 1)),
(nme.wrapUnitArray, "toUnitVarArgs", jstpe.ArrayTypeRef(jstpe.ClassRef(jswkn.BoxedUnitClass), 1)),
(nme.wrapBooleanArray, "toBooleanVarArgs", jstpe.ArrayTypeRef(jstpe.BooleanRef, 1)),
(nme.wrapCharArray, "toCharVarArgs", jstpe.ArrayTypeRef(jstpe.CharRef, 1)),
(nme.wrapByteArray, "toByteVarArgs", jstpe.ArrayTypeRef(jstpe.ByteRef, 1)),
(nme.wrapShortArray, "toShortVarArgs", jstpe.ArrayTypeRef(jstpe.ShortRef, 1)),
(nme.wrapIntArray, "toIntVarArgs", jstpe.ArrayTypeRef(jstpe.IntRef, 1)),
(nme.wrapLongArray, "toLongVarArgs", jstpe.ArrayTypeRef(jstpe.LongRef, 1)),
(nme.wrapFloatArray, "toFloatVarArgs", jstpe.ArrayTypeRef(jstpe.FloatRef, 1)),
(nme.wrapDoubleArray, "toDoubleVarArgs", jstpe.ArrayTypeRef(jstpe.DoubleRef, 1))
)

items.map { case (wrapArrayName, simpleName, argTypeRef) =>
val wrapArraySym = getMemberMethod(wrapArrayModule, wrapArrayName)
val toVarArgsName = MethodName(simpleName, argTypeRef :: Nil, SeqClassRef)
wrapArraySym -> toVarArgsName
}.toMap
}

def unapply(tree: Apply): Option[Tree] = tree match {
case Apply(wrapArray_?, List(wrapped))
if isWrapArray(wrapArray_?.symbol) =>
if wrapArraySymToToVarArgsName.contains(wrapArray_?.symbol) =>
Some(wrapped)
case _ =>
None
Expand Down
29 changes: 23 additions & 6 deletions compiler/src/test/scala/org/scalajs/nscplugin/test/OptimizationTest.scala
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Expand Up @@ -85,9 +85,10 @@ class OptimizationTest extends JSASTTest {
val d = js.Array(Nil)
val e = js.Array(new VC(151189))
}
""".
hasNot("any of the wrapArray methods") {
""".hasNot("any of the wrapArray methods") {
case WrapArrayCall() =>
}.hasNot("any toVarArgs calls") {
case ToVarArgsCall() =>
}
}

Expand All @@ -108,9 +109,10 @@ class OptimizationTest extends JSASTTest {
val d = List(Nil)
val e = List(new VC(151189))
}
""".
hasNot("any of the wrapArray methods") {
""".hasNot("any of the wrapArray methods") {
case WrapArrayCall() =>
}.hasExactly(5, "toVarArgs calls") {
case ToVarArgsCall() =>
}

/* #2265 and #2741:
Expand All @@ -136,9 +138,10 @@ class OptimizationTest extends JSASTTest {
def single(x: Int, ys: Int*): Int = x + ys.size
def multiple(x: Int)(ys: Int*): Int = x + ys.size
}
""".
hasNot("any of the wrapArray methods") {
""".hasNot("any of the wrapArray methods") {
case WrapArrayCall() =>
}.hasExactly(3, "toVarArgs calls") {
case ToVarArgsCall() =>
}

/* Make sure our wrapper matcher has the right name.
Expand All @@ -162,6 +165,8 @@ class OptimizationTest extends JSASTTest {
}
sanityCheckCode.has("one of the wrapArray methods") {
case WrapArrayCall() =>
}.hasNot("any toVarArgs calls") {
case ToVarArgsCall() =>
}
}

Expand Down Expand Up @@ -697,6 +702,7 @@ class OptimizationTest extends JSASTTest {
object OptimizationTest {

private val ArrayModuleClass = ClassName("scala.Array$")
private val ScalaJSRunTimeModuleClass = ClassName("scala.scalajs.runtime.package$")

private val applySimpleMethodName = SimpleMethodName("apply")

Expand All @@ -718,4 +724,15 @@ object OptimizationTest {
}
}

private object ToVarArgsCall {
def unapply(tree: js.Apply): Boolean = {
tree.method.name.simpleName.nameString.endsWith("VarArgs") && {
tree.receiver match {
case js.LoadModule(ScalaJSRunTimeModuleClass) => true
case _ => false
}
}
}
}

}
34 changes: 34 additions & 0 deletions library/src/main/scala-new-collections/scala/scalajs/runtime/Compat.scala
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Expand Up @@ -13,6 +13,7 @@
package scala.scalajs.runtime

import scala.collection.IterableOnce
import scala.collection.immutable.ArraySeq

import scala.scalajs.js

Expand All @@ -32,4 +33,37 @@ private[runtime] object Compat {
}
}

@inline def toGenericVarArgsWasmImpl[T](xs: Array[T]): Seq[T] =
ArraySeq.unsafeWrapArray(xs)

@inline def toRefVarArgsWasmImpl[T <: AnyRef](xs: Array[T]): Seq[T] =
new ArraySeq.ofRef[T](xs)

@inline def toUnitVarArgsWasmImpl(xs: Array[Unit]): Seq[Unit] =
new ArraySeq.ofUnit(xs)

@inline def toBooleanVarArgsWasmImpl(xs: Array[Boolean]): Seq[Boolean] =
new ArraySeq.ofBoolean(xs)

@inline def toCharVarArgsWasmImpl(xs: Array[Char]): Seq[Char] =
new ArraySeq.ofChar(xs)

@inline def toByteVarArgsWasmImpl(xs: Array[Byte]): Seq[Byte] =
new ArraySeq.ofByte(xs)

@inline def toShortVarArgsWasmImpl(xs: Array[Short]): Seq[Short] =
new ArraySeq.ofShort(xs)

@inline def toIntVarArgsWasmImpl(xs: Array[Int]): Seq[Int] =
new ArraySeq.ofInt(xs)

@inline def toLongVarArgsWasmImpl(xs: Array[Long]): Seq[Long] =
new ArraySeq.ofLong(xs)

@inline def toFloatVarArgsWasmImpl(xs: Array[Float]): Seq[Float] =
new ArraySeq.ofFloat(xs)

@inline def toDoubleVarArgsWasmImpl(xs: Array[Double]): Seq[Double] =
new ArraySeq.ofDouble(xs)

}
35 changes: 35 additions & 0 deletions library/src/main/scala-old-collections/scala/scalajs/runtime/Compat.scala
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Expand Up @@ -13,6 +13,8 @@
package scala.scalajs.runtime

import scala.collection.GenTraversableOnce
import scala.collection.mutable.WrappedArray

import scala.scalajs.js

private[runtime] object Compat {
Expand All @@ -32,4 +34,37 @@ private[runtime] object Compat {
}
}

@inline def toGenericVarArgsWasmImpl[T](xs: Array[T]): Seq[T] =
WrappedArray.make(xs)

@inline def toRefVarArgsWasmImpl[T <: AnyRef](xs: Array[T]): Seq[T] =
new WrappedArray.ofRef[T](xs)

@inline def toUnitVarArgsWasmImpl(xs: Array[Unit]): Seq[Unit] =
new WrappedArray.ofUnit(xs)

@inline def toBooleanVarArgsWasmImpl(xs: Array[Boolean]): Seq[Boolean] =
new WrappedArray.ofBoolean(xs)

@inline def toCharVarArgsWasmImpl(xs: Array[Char]): Seq[Char] =
new WrappedArray.ofChar(xs)

@inline def toByteVarArgsWasmImpl(xs: Array[Byte]): Seq[Byte] =
new WrappedArray.ofByte(xs)

@inline def toShortVarArgsWasmImpl(xs: Array[Short]): Seq[Short] =
new WrappedArray.ofShort(xs)

@inline def toIntVarArgsWasmImpl(xs: Array[Int]): Seq[Int] =
new WrappedArray.ofInt(xs)

@inline def toLongVarArgsWasmImpl(xs: Array[Long]): Seq[Long] =
new WrappedArray.ofLong(xs)

@inline def toFloatVarArgsWasmImpl(xs: Array[Float]): Seq[Float] =
new WrappedArray.ofFloat(xs)

@inline def toDoubleVarArgsWasmImpl(xs: Array[Double]): Seq[Double] =
new WrappedArray.ofDouble(xs)

}
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