Merge pull request #12657 from dotty-staging/sjs-default-accessors-bridges-in-non-native-js-classes

Fix #12572: Ignore default accessor bridges in non-native JS classes.

Author: smarter

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

@@ -18,6 +18,7 @@ import Decorators._
 import Flags._
 import dotty.tools.dotc.ast.Trees._
 import Names._
+import NameKinds.DefaultGetterName
 import Types._
 import Symbols._
 import Denotations._
@@ -1069,6 +1070,14 @@ class JSCodeGen()(using genCtx: Context) {
       } else if (sym.isJSNativeCtorDefaultParam) {
         // #11592
         None
+      } else if (sym.is(Bridge) && sym.name.is(DefaultGetterName) && currentClassSym.isNonNativeJSClass) {
+        /* #12572 Bridges for default accessors in non-native JS classes must not be emitted,
+         * because they call another default accessor, making their entire body an
+         * <undefined-param> that cannot be eliminated.
+         * Such methods are never called anyway, because they are filtered out in
+         * JSExportsGen.defaultGetterDenot().
+         */
+        None
       } else /*if (sym.isClassConstructor && isHijackedBoxedClass(sym.owner)) {
         None
       } else*/ {

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

@@ -774,7 +774,7 @@ final class JSExportsGen(jsCodeGen: JSCodeGen)(using Context) {
     else sym.owner
 
   private def defaultGetterDenot(targetSym: Symbol, sym: Symbol, paramIndex: Int): Denotation =
-    targetSym.info.member(DefaultGetterName(sym.name.asTermName, paramIndex))
+    targetSym.info.memberBasedOnFlags(DefaultGetterName(sym.name.asTermName, paramIndex), excluded = Bridge)
 
   private def defaultGetterDenot(sym: Symbol, paramIndex: Int): Denotation =
     defaultGetterDenot(targetSymForDefaultGetter(sym), sym, paramIndex)

tests/sjs-junit/test/org/scalajs/testsuite/compiler/RegressionTestScala3.scala

@@ -35,6 +35,10 @@ class RegressionTestScala3 {
 
     assertEquals(5, foo(5)(4))
   }
+
+  @Test def defaultAccessorBridgesIssue12572(): Unit = {
+    new MyPromiseIssue12572[Int](5)
+  }
 }
 
 object RegressionTestScala3 {
@@ -53,6 +57,25 @@ object RegressionTestScala3 {
   class RangeErrorIssue11592(msg: String = js.native) extends js.Object {
     val message: String = js.native
   }
+
+  class MyPromiseIssue12572[T](t: T) extends js.Promise[T]((resolve, reject) => resolve(t)) {
+    override def `then`[S](
+        onFulfilled: js.Function1[T, S | js.Thenable[S]],
+        onRejected: js.UndefOr[js.Function1[scala.Any, S | js.Thenable[S]]] = js.undefined): js.Promise[S] = {
+      ???
+    }
+
+    override def `then`[S >: T](
+        onFulfilled: Unit,
+        onRejected: js.UndefOr[js.Function1[scala.Any, S | js.Thenable[S]]]): js.Promise[S] = {
+      ???
+    }
+
+    override def `catch`[S >: T](
+        onRejected: js.UndefOr[js.Function1[scala.Any, S | js.Thenable[S]]] = js.undefined): js.Promise[S] = {
+      ???
+    }
+  }
 }
 
 // This class needs to be at the top-level, not in an object, to reproduce the issue