Fix #5588: Add regression test

Author: nicolasstucki

tests/pos/i5588a.scala

@@ -0,0 +1,22 @@
+object TestMain {
+  def main(args: Array[String]): Unit = {
+    testExtensionProperty()
+  }
+
+  case class Foo(var foo: String)
+
+  object fooExt {
+    // define `Foo`-extension property with getter and setter delegating to `Foo.foo`
+    extension (thisFoo: Foo) def fooExt: String = thisFoo.foo
+    extension (thisFoo: Foo) def fooExt_= (value: String): Unit = { thisFoo.foo = value }
+  }
+
+  def testExtensionProperty(): Unit = {
+    import fooExt._
+    val foo = Foo("initVal")
+    assert(foo.fooExt == "initVal")
+    foo.fooExt = "updatedVal"
+    assert(foo.foo == "updatedVal")
+    assert(foo.fooExt == "updatedVal")
+  }
+}

tests/pos/i5588b.scala

@@ -0,0 +1,22 @@
+object TestMain2 {
+  def main(args: Array[String]): Unit = {
+    testExtensionProperty()
+  }
+
+  case class Foo(var foo: String)
+
+  implicit object fooExt {
+    // define `Foo`-extension property with getter and setter delegating to `Foo.foo`
+    extension (thisFoo: Foo) def fooExt: String = thisFoo.foo
+    extension (thisFoo: Foo) def fooExt_= (value: String): Unit = { thisFoo.foo = value }
+  }
+
+  def testExtensionProperty(): Unit = {
+    //import fooExt._
+    val foo = Foo("initVal")
+    assert(foo.fooExt == "initVal")
+    foo.fooExt = "updatedVal"
+    assert(foo.foo == "updatedVal")
+    assert(foo.fooExt == "updatedVal")
+  }
+}