Backport "Change isStatic to isStaticOwner in hasLocalInstantiation" …

…to LTS (#20974)

Backports #19803 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

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

@@ -227,7 +227,7 @@ object ExplicitOuter {
   private def hasLocalInstantiation(cls: ClassSymbol)(using Context): Boolean =
     // Modules are normally locally instantiated, except if they are declared in a trait,
     // in which case they will be instantiated in the classes that mix in the trait.
-    cls.owner.ownersIterator.takeWhile(!_.isStatic).exists(_.isTerm)
+    cls.owner.ownersIterator.takeWhile(!_.isStaticOwner).exists(_.isTerm)
     || cls.is(Private, butNot = Module)
     || cls.is(Module) && !cls.owner.is(Trait)
 

tests/generic-java-signatures/outer-ref-elimination.check

@@ -0,0 +1,9 @@
+List(public T1$C1())
+List(public T2$$anon$1$C2())
+List(public T3$C3$1())
+List(public T4$$anon$2$C4())
+List(public T5$C5(T5))
+List(public T6$$anon$3$C6())
+List(public T7$C7$1())
+List(public T8$$anon$4$C8())
+List(public T9$C9$1(T9))

tests/generic-java-signatures/outer-ref-elimination.scala

@@ -0,0 +1,41 @@
+// This test checks that references to outer classes in inner classes are
+// eliminated in some cases when they are not used. This is done in the
+// ExplicitOuter phase. See issue #19569 for discussions.
+
+object helper {
+  def test(cls: Class[?]) = println(cls.getDeclaredConstructors.toList)
+}
+
+import helper.test
+
+object T1 { class C1; test(classOf[C1]) }
+object T2 { new AnyRef { class C2; test(classOf[C2]) } }
+object T3 { def t3(): Unit = { class C3; test(classOf[C3]) } }
+object T4 { def t4(): Unit = new AnyRef { class C4; test(classOf[C4]) } }
+
+// The outer reference in C5 is not eliminated because C5 is publicly
+// accessible as a member of T5. Therefore, its constructor needs to conform
+// to the expected signature, with the outer reference parameter.
+class T5 { class C5; test(classOf[C5]) }
+
+class T6 { new AnyRef { class C6; test(classOf[C6]) } }
+class T7 { def t7(): Unit = { class C7; test(classOf[C7]) } }
+class T8 { def t8(): Unit = new AnyRef { class C8; test(classOf[C8]) } }
+
+// Here, the outer reference in C9 is not eliminated because C9 needs to access
+// the field x.
+class T9 { var x = 451; def t9(): Unit = { class C9 {def getX = x}; test(classOf[C9])} }
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    T1
+    T2
+    T3.t3()
+    T4.t4()
+    new T5()
+    new T6()
+    new T7().t7()
+    new T8().t8()
+    new T9().t9()
+  }
+}