Fix #4496: call ensureAccessible to bypass class-level accessibility

library/src/scala/reflect/Selectable.scala

@@ -5,6 +5,7 @@ class Selectable(val receiver: Any) extends AnyVal with scala.Selectable {
     val rcls = receiver.getClass
     try {
       val fld = rcls.getField(name)
+      ensureAccessible(fld)
       fld.get(receiver)
     }
     catch {
@@ -17,6 +18,7 @@ class Selectable(val receiver: Any) extends AnyVal with scala.Selectable {
     val rcls = receiver.getClass
     val paramClasses = paramTypes.map(_.runtimeClass)
     val mth = rcls.getMethod(name, paramClasses: _*)
+    ensureAccessible(mth)
     paramTypes.length match {
       case 0 => () =>
         mth.invoke(receiver)

tests/neg/i4496b.scala

@@ -0,0 +1,25 @@
+import scala.reflect.Selectable.reflectiveSelectable
+
+trait Foo1 { val a: Int }
+trait Foo2 { def a: Int }
+trait Foo3 { var a: Int }
+
+object TestStructuralVar {
+  type T0 = {var a: Int} // error
+  object TestStructuralVar {
+    type T = {val a: Int; def a_=(x: Int): Unit}
+    def upcast1(v: Foo1): T = v // error
+    def upcast2(v: Foo2): T = v // error
+    def upcast3(v: Foo3): T = v
+    def verify(v: T) = ()
+    def test(): Unit = {
+      verify(upcast1(new Foo1 { val a = 10 }))
+      verify(upcast2(new Foo2 { val a = 10 }))
+      verify(upcast3(new Foo3 { var a = 10 }))
+    }
+  }
+
+  def main(args: Array[String]): Unit = {
+    TestStructuralVar.test()
+  }
+}

tests/run/i4496b.scala

@@ -0,0 +1,116 @@
+import scala.reflect.Selectable.reflectiveSelectable
+
+trait Foo1 { val a: Int }
+trait Foo2 { def a: Int }
+trait Foo3 { var a: Int }
+
+object Test {
+  private class FooBar1 extends Foo1 { val a: Int = 10 }
+  private class FooBar2 extends Foo2 { def a: Int = 10 }
+  private class FooBar3 extends Foo3 { var a: Int = 10 }
+
+  private class Bar1 { val a: Int = 10 }
+  private class Bar2 { def a: Int = 10 }
+  private class Bar3 { var a: Int = 10 }
+
+  object TestStructuralVal {
+    // This test is also an (abstracted) motivating example.
+
+    // Consider one module upcasting all these instances to T. These casts are clearly well-typed.
+    type T = {val a: Int}
+    def upcast1(v: Foo1): T = v
+    def upcast2(v: Foo2): T = v
+    def upcast3(v: Foo3): T = v
+
+    // These accesses are also clearly well-typed
+    def consume(v: T) = v.a
+    inline def consumeInl(v: T) = v.a
+    def verify(v: T) = {
+      assert(consume(v) == 10)
+      assert(consumeInl(v) == 10)
+      assert(v.a == 10)
+    }
+
+    def test(): Unit = {
+      // These calls are also clearly well-typed, hence can't be rejected.
+      verify(upcast1(new Foo1 { val a = 10 }))
+      verify(upcast2(new Foo2 { val a = 10 }))
+      verify(upcast3(new Foo3 { var a = 10 }))
+      // Ditto, so we must override access control to the class.
+      verify(upcast1(new FooBar1))
+      verify(upcast2(new FooBar2))
+      verify(upcast3(new FooBar3))
+
+      // Other testcases
+      verify(new {val a = 10} : T)
+      verify(new {var a = 10} : T)
+      verify(new {def a = 10} : T)
+
+      verify(new Bar1 : T)
+      verify(new Bar2 : T)
+      verify(new Bar3 : T)
+    }
+  }
+
+  object TestStructuralDef {
+    type T = {def a: Int}
+    def upcast1(v: Foo1): T = v
+    def upcast2(v: Foo2): T = v
+    def upcast3(v: Foo3): T = v
+    def consume(v: T) = v.a
+    inline def consumeInl(v: T) = v.a
+    def verify(v: T) = {
+      assert(consume(v) == 10)
+      assert(consumeInl(v) == 10)
+      assert(v.a == 10)
+    }
+
+    def test(): Unit = {
+      verify(upcast1(new Foo1 { val a = 10 }))
+      verify(upcast2(new Foo2 { val a = 10 }))
+      verify(upcast3(new Foo3 { var a = 10 }))
+
+      verify(upcast1(new FooBar1))
+      verify(upcast2(new FooBar2))
+      verify(upcast3(new FooBar3))
+
+      verify(new {val a = 10} : T)
+      verify(new {var a = 10} : T)
+      verify(new {def a = 10} : T)
+
+      verify(new Bar1 : T)
+      verify(new Bar2 : T)
+      verify(new Bar3 : T)
+    }
+  }
+
+  object TestStructuralVar {
+    type T = {val a: Int; def a_=(x: Int): Unit}
+    def upcast3(v: Foo3): T = v
+    def consume(v: T) = v.a
+    inline def consumeInl(v: T) = v.a
+    def verify(v: T) = {
+      assert(consume(v) == 10)
+      assert(consumeInl(v) == 10)
+      assert(v.a == 10)
+      // Pending, per https://github.com/lampepfl/dotty/issues/4528.
+      // v.a = 11
+      // assert(consume(v) == 11)
+      // assert(consumeInl(v) == 11)
+      // assert(v.a == 11)
+    }
+
+    def test(): Unit = {
+      verify(upcast3(new Foo3 { var a = 10 }))
+      verify(upcast3(new FooBar3))
+      verify(new {var a = 10} : T)
+      verify(new Bar3 : T)
+    }
+  }
+
+  def main(args: Array[String]): Unit = {
+    TestStructuralVal.test()
+    TestStructuralDef.test()
+    TestStructuralVar.test()
+  }
+}