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Commit 256e684

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Scala.js: Handle @JSName annots with constant-folded arguments.
Previously, if an `@JSName` annotation had an argument that was not a literal, but a reference to a constant expression (such as a `final val`), it would not be constant-folded in the generated Scala.js IR. This produced worse code than necessary. For Wasm, it was particularly bad, as the names must then be evaluated on the Wasm side instead of being pushed to the custom JS helpers.
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2 files changed

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‎compiler/src/dotty/tools/dotc/transform/sjs/JSSymUtils.scala

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -164,9 +164,9 @@ object JSSymUtils {
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sym.getAnnotation(jsdefn.JSNameAnnot).fold[JSName] {
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JSName.Literal(defaultJSName)
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} { annotation =>
167-
annotation.arguments.head match {
168-
case Literal(Constant(name: String)) => JSName.Literal(name)
169-
case tree => JSName.Computed(tree.symbol)
167+
annotation.argumentConstantString(0) match {
168+
case Some(name) => JSName.Literal(name)
169+
case None => JSName.Computed(annotation.arguments.head.symbol)
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}
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}
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}

‎compiler/src/dotty/tools/dotc/transform/sjs/PrepJSInterop.scala

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -154,7 +154,7 @@ class PrepJSInterop extends MacroTransform with IdentityDenotTransformer { thisP
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}
155155

156156
checkJSNameAnnots(sym)
157-
constFoldJSExportTopLevelAndStaticAnnotations(sym)
157+
constantFoldJSAnnotations(sym)
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markExposedIfRequired(tree.symbol)
160160

@@ -1089,17 +1089,18 @@ class PrepJSInterop extends MacroTransform with IdentityDenotTransformer { thisP
10891089
}
10901090
}
10911091

1092-
/** Constant-folds arguments to `@JSExportTopLevel` and `@JSExportStatic`.
1092+
/** Constant-folds arguments to `@JSName`, `@JSExportTopLevel` and `@JSExportStatic`.
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*
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* Unlike scalac, dotc does not constant-fold expressions in annotations.
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* Our back-end needs to have access to the arguments to those two
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* annotations as literal strings, so we specifically constant-fold them
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* here.
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*/
1099-
private def constFoldJSExportTopLevelAndStaticAnnotations(sym: Symbol)(using Context): Unit = {
1099+
private def constantFoldJSAnnotations(sym: Symbol)(using Context): Unit = {
11001100
val annots = sym.annotations
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val newAnnots = annots.mapConserve { annot =>
1102-
if (annot.symbol == jsdefn.JSExportTopLevelAnnot || annot.symbol == jsdefn.JSExportStaticAnnot) {
1102+
if (annot.symbol == jsdefn.JSExportTopLevelAnnot || annot.symbol == jsdefn.JSExportStaticAnnot ||
1103+
annot.symbol == jsdefn.JSNameAnnot) {
11031104
annot.tree match {
11041105
case app @ Apply(fun, args) =>
11051106
val newArgs = args.mapConserve { arg =>
@@ -1109,7 +1110,7 @@ class PrepJSInterop extends MacroTransform with IdentityDenotTransformer { thisP
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case _ =>
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arg.tpe.widenTermRefExpr.normalized match {
11111112
case ConstantType(c) => Literal(c).withSpan(arg.span)
1112-
case _ => arg// PrepJSExports will emit an error for those cases
1113+
case _ => arg
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}
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}
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}

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