wip: undefOr2ops implicit conversion, more complete erasure

Author: smarter

compiler/src/dotty/tools/backend/sjs/JSDefinitions.scala

@@ -58,6 +58,7 @@ final class JSDefinitions()(using Context) {
     def PseudoUnion_from(using Context) = PseudoUnion_fromR.symbol
     @threadUnsafe lazy val PseudoUnion_fromTypeConstructorR = PseudoUnionModule.requiredMethodRef("fromTypeConstructor")
     def PseudoUnion_fromTypeConstructor(using Context) = PseudoUnion_fromTypeConstructorR.symbol
+    @threadUnsafe lazy val PseudoUnion_undefOr2opsR = PseudoUnionModule.requiredMethodRef("undefOr2ops")
 
   @threadUnsafe lazy val JSArrayType: TypeRef = requiredClassRef("scala.scalajs.js.Array")
   def JSArrayClass(using Context) = JSArrayType.symbol.asClass

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -11,6 +11,7 @@ import collection.mutable
 import Denotations.SingleDenotation
 import util.{SimpleIdentityMap, SourceFile, NoSource}
 import typer.ImportInfo.RootRef
+import backend.sjs.JSDefinitions
 
 import scala.annotation.tailrec
 
@@ -1344,14 +1345,24 @@ class Definitions {
   private val PredefImportFns: RootRef =
     RootRef(() => ScalaPredefModule.termRef, isPredef=true)
 
+  @tu private lazy val ScalaJsRootImportFn: RootRef =
+    RootRef(() => JSDefinitions.jsdefn.PseudoUnionModuleRef)
+    // TODO: Doesn't work because of the way ImportInfo#rootImport works currently
+    // RootRef(() => JSDefinitions.jsdefn.PseudoUnion_undefOr2ops)
+
   @tu private lazy val JavaRootImportFns: List[RootRef] =
     if ctx.settings.YnoImports.value then Nil
     else JavaImportFns
 
   @tu private lazy val ScalaRootImportFns: List[RootRef] =
-    if ctx.settings.YnoImports.value then Nil
-    else if ctx.settings.YnoPredef.value then ScalaImportFns
-    else ScalaImportFns :+ PredefImportFns
+    if ctx.settings.YnoImports.value then
+      Nil
+    else if ctx.settings.YnoPredef.value then
+      ScalaImportFns
+    else if !ctx.settings.scalajs.value then
+      ScalaImportFns :+ PredefImportFns
+    else
+      ScalaImportFns :+ PredefImportFns :+ ScalaJsRootImportFn
 
   @tu private lazy val JavaRootImportTypes: List[TermRef] = JavaRootImportFns.map(_.refFn())
   @tu private lazy val ScalaRootImportTypes: List[TermRef] = ScalaRootImportFns.map(_.refFn())

compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -593,7 +593,10 @@ class TypeErasure(sourceLanguage: SourceLanguage, semiEraseVCs: Boolean, isConst
     val tp1 =
       if sourceLanguage.isScala2 && ctx.settings.scalajs.value then
         val eraseAsPseudoUnion = new TypeMap:
-          def apply(tp: Type) = tp match
+          // TODO: This isn't good enough since an OrType might be
+          // hidden behind a bound for example; we might have no
+          // choice but to move this logic to the TypeErasure class.
+          def apply(tp: Type) = tp.dealias match
             case tp: OrType =>
               JSDefinitions.jsdefn.PseudoUnionType
             case tp =>

compiler/src/dotty/tools/dotc/typer/ImportInfo.scala

@@ -18,6 +18,9 @@ import Decorators._
 object ImportInfo {
 
   case class RootRef(refFn: () => TermRef, isPredef: Boolean = false)
+  // TODO: Replace by one of those:
+  // case class RootRef(refFn: () => TermRef, selector: Option[untpd.ImportSelector])
+  // case class RootRef(refFn: () => TermRef, selector: Tree = EmptyTree)
 
   /** The import info for a root import */
   def rootImport(ref: RootRef)(using Context): ImportInfo =