Scala.js: Add support for js.constructorOf[T].

To do this, we add a new mini-phase that rewrites calls of the form

  scala.scalajs.js.constructor[T]

to

  scala.scalajs.runtime.constructorOf(classOf[T])

The back-end already knew how to compile calls to
`runtime.constructorOf`, so there were no changes needed there.

The new mini-phase will also serve in the future for handling
inner and local JS classes.

Author: sjrd

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -72,6 +72,7 @@ class Compiler {
     List(new ElimOpaque,             // Turn opaque into normal aliases
          new TryCatchPatterns,       // Compile cases in try/catch
          new PatternMatcher,         // Compile pattern matches
+         new ExplicitJSClasses,      // Make all JS classes explicit (Scala.js only)
          new ExplicitOuter,          // Add accessors to outer classes from nested ones.
          new ExplicitSelf,           // Make references to non-trivial self types explicit as casts
          new StringInterpolatorOpt,  // Optimizes raw and s string interpolators by rewriting them to string concatentations

compiler/src/dotty/tools/dotc/transform/ExplicitJSClasses.scala

@@ -0,0 +1,64 @@
+package dotty.tools
+package dotc
+package transform
+
+import MegaPhase._
+import core.DenotTransformers._
+import core.Symbols._
+import core.Contexts._
+import core.Phases._
+import core.Types._
+import core.Flags._
+import core.Decorators._
+import core.StdNames.nme
+import core.Names._
+import core.NameOps._
+import ast.Trees._
+import SymUtils._
+import dotty.tools.dotc.ast.tpd
+
+import dotty.tools.backend.sjs.JSDefinitions.jsdefn
+
+/** This phase makes all JS classes explicit (their definitions and references to them).
+ *
+ *  Ultimately, this will be the equivalent of the two phases `ExplicitInnerJS`
+ *  and `ExplicitLocalJS` from Scala 2. Currently, this phase only performs the
+ *  following transformations:
+ *
+ *  - Rewrite `js.constructorOf[T]` into `scala.scalajs.runtime.constructorOf(classOf[T])`,
+ *    where the `classOf[T]` is represented as a `Literal`.
+ */
+class ExplicitJSClasses extends MiniPhase with InfoTransformer { thisPhase =>
+  import ExplicitJSClasses._
+  import ast.tpd._
+
+  override def phaseName: String = ExplicitJSClasses.name
+
+  override def isEnabled(using Context): Boolean =
+    ctx.settings.scalajs.value
+
+  override def runsAfter: Set[String] = Set(PatternMatcher.name, HoistSuperArgs.name)
+
+  override def changesMembers: Boolean = true // the phase adds fields for inner JS classes
+
+  override def transformInfo(tp: Type, sym: Symbol)(using Context): Type = {
+    // Currently we don't do anything here. Eventually we'll add fields for inner JS classes.
+    tp
+  }
+
+  override def mayChange(sym: Symbol)(using Context): Boolean =
+    sym.isClass && !sym.is(JavaDefined)
+
+  override def transformTypeApply(tree: TypeApply)(using Context): tpd.Tree = {
+    tree match {
+      case TypeApply(fun, tpt :: Nil) if fun.symbol == jsdefn.JSPackage_constructorOf =>
+        ref(jsdefn.Runtime_constructorOf).appliedTo(clsOf(tpt.tpe))
+      case _ =>
+        tree
+    }
+  }
+}
+
+object ExplicitJSClasses {
+  val name: String = "explicitJSClasses"
+}

project/Build.scala

@@ -1065,17 +1065,16 @@ object Build {
           ++ (dir / "shared/src/test/require-jdk7/org/scalajs/testsuite/javalib/util" ** "*.scala").get
 
           ++ (dir / "js/src/test/scala/org/scalajs/testsuite/compiler" ** (("*.scala": FileFilter)
-            -- "InteroperabilityTest.scala" // various compile errors
-            -- "OptimizerTest.scala" // compile errors: false + string and () + string
-            -- "ReflectionTest.scala" // tests fail
+            -- "InteroperabilityTest.scala" // various compile errors, pending update upstream
+            -- "OptimizerTest.scala" // compile errors: false + string and () + string, pending update upstream
+            -- "ReflectionTest.scala" // tests fail (wrong load spec for JS globals)
             -- "RegressionJSTest.scala" // non-native JS classes
             -- "RuntimeTypesTest.scala" // compile errors: no ClassTag for Null and Nothing
             )).get
 
           ++ (dir / "js/src/test/scala/org/scalajs/testsuite/javalib" ** (("*.scala": FileFilter)
             -- "FormatterJSTest.scala" // compile error with the f"" interpolator
             -- "ObjectJSTest.scala" // non-native JS classes
-            -- "ThrowableJSTest.scala" // test fails ("java.lang.Error: stub") because it uses js.constructorOf
             )).get
 
           ++ (dir / "js/src/test/scala/org/scalajs/testsuite/jsinterop" ** (("*.scala": FileFilter)
@@ -1084,15 +1083,14 @@ object Build {
             -- "ExportsTest.scala" // JS exports
             -- "IterableTest.scala" // non-native JS classes
             -- "JSExportStaticTest.scala" // JS exports
-            -- "JSNativeInPackage.scala" // IR checking errors
+            -- "JSNativeInPackage.scala" // tests fail (wrong load spec for JS globals)
             -- "JSOptionalTest.scala" // non-native JS classes
             -- "JSSymbolTest.scala" // non-native JS classes
             -- "MiscInteropTest.scala" // non-native JS classes
             -- "ModulesWithGlobalFallbackTest.scala" // non-native JS classes
             -- "NestedJSClassTest.scala" // non-native JS classes
             -- "NonNativeJSTypeTest.scala" // non-native JS classes
             -- "PromiseMock.scala" // non-native JS classes
-            -- "SpecialTest.scala" // test fails ("java.lang.Error: stub") because it uses js.constructorOf
             )).get
 
           ++ (dir / "js/src/test/scala/org/scalajs/testsuite/junit" ** (("*.scala": FileFilter)
@@ -1105,7 +1103,7 @@ object Build {
 
           ++ (dir / "js/src/test/scala/org/scalajs/testsuite/library" ** (("*.scala": FileFilter)
             -- "BigIntTest.scala" // Ambiguous reference because of new non-shadowing rule in Scala 3, pending update upstream
-            -- "ObjectTest.scala" // compile errors
+            -- "ObjectTest.scala" // compile errors caused by #9588
             -- "StackTraceTest.scala" // would require `npm install source-map-support`
             -- "UnionTypeTest.scala" // requires a Scala 2 macro
             )).get