Simplify expression per review and add tests

Author: som-snytt

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -825,28 +825,23 @@ object SymDenotations {
 
       /** Is protected access to target symbol permitted? */
       def isProtectedAccessOK: Boolean =
-        def fail(str: => String): false =
+        inline def fail(str: String): false =
           if whyNot != null then whyNot.append(str)
           false
         val cls = owner.enclosingSubClass
         if !cls.exists then
-          val encl = if !ctx.owner.isConstructor then ctx else ctx.outersIterator.dropWhile(_.owner.isConstructor).next()
-          fail(
-            i"""
-               | Access to protected $this not permitted because enclosing ${encl.owner.enclosingClass.showLocated}
+          val encl = if ctx.owner.isConstructor then ctx.owner.enclosingClass.owner.enclosingClass else ctx.owner.enclosingClass
+          fail(i"""
+               | Access to protected $this not permitted because enclosing ${encl.showLocated}
                | is not a subclass of ${owner.showLocated} where target is defined""")
-        else if
-          !(  isType // allow accesses to types from arbitrary subclasses fixes #4737
-           || pre.derivesFrom(cls)
-           || isConstructor
-           || owner.is(ModuleClass) // don't perform this check for static members
-           )
-        then
-          fail(
-            i"""
+        else if isType || pre.derivesFrom(cls) || isConstructor || owner.is(ModuleClass) then
+          // allow accesses to types from arbitrary subclasses fixes #4737
+          // don't perform this check for static members
+          true
+        else
+          fail(i"""
                | Access to protected ${symbol.show} not permitted because prefix type ${pre.widen.show}
                | does not conform to ${cls.showLocated} where the access takes place""")
-        else true
       end isProtectedAccessOK
 
       if pre eq NoPrefix then true

tests/neg/i7709.check

@@ -4,9 +4,45 @@
   |                  class Y in object X cannot be accessed as a member of X.type from class B.
   |                   Access to protected class Y not permitted because enclosing object A
   |                   is not a subclass of object X where target is defined
--- Error: tests/neg/i7709.scala:10:18 ----------------------------------------------------------------------------------
-10 |  def y  = new xx.Y  // error
+-- Error: tests/neg/i7709.scala:6:21 -----------------------------------------------------------------------------------
+6 |  class B2 extends X.Y: // error
+  |                   ^^^
+  |                   class Y in object X cannot be accessed as a member of X.type from class B2.
+  |                    Access to protected class Y not permitted because enclosing object A
+  |                    is not a subclass of object X where target is defined
+-- Error: tests/neg/i7709.scala:9:28 -----------------------------------------------------------------------------------
+9 |  class B4 extends B3(new X.Y) // error
+  |                          ^^^
+  |                          class Y in object X cannot be accessed as a member of X.type from class B4.
+  |                           Access to protected class Y not permitted because enclosing object A
+  |                           is not a subclass of object X where target is defined
+-- Error: tests/neg/i7709.scala:11:34 ----------------------------------------------------------------------------------
+11 |    def this(n: Int) = this(new X.Y().toString) // error
+   |                                ^^^
+   |                                class Y in object X cannot be accessed as a member of X.type from class B5.
+   |                                 Access to protected class Y not permitted because enclosing object A
+   |                                 is not a subclass of object X where target is defined
+-- Error: tests/neg/i7709.scala:13:20 ----------------------------------------------------------------------------------
+13 |  class B extends X.Y // error
+   |                  ^^^
+   |                  class Y in object X cannot be accessed as a member of X.type from class B.
+   |                   Access to protected class Y not permitted because enclosing trait T
+   |                   is not a subclass of object X where target is defined
+-- Error: tests/neg/i7709.scala:18:18 ----------------------------------------------------------------------------------
+18 |  def y  = new xx.Y  // error
    |               ^^^^
    |               class Y cannot be accessed as a member of XX from class C.
    |                Access to protected class Y not permitted because enclosing class C
    |                is not a subclass of class XX where target is defined
+-- Error: tests/neg/i7709.scala:23:20 ----------------------------------------------------------------------------------
+23 |    def y  = new xx.Y  // error
+   |                 ^^^^
+   |                 class Y cannot be accessed as a member of XX from class D.
+   |                  Access to protected class Y not permitted because enclosing class D
+   |                  is not a subclass of class XX where target is defined
+-- Error: tests/neg/i7709.scala:31:20 ----------------------------------------------------------------------------------
+31 |  class Q extends X.Y // error
+   |                  ^^^
+   |                  class Y in object X cannot be accessed as a member of p.X.type from class Q.
+   |                   Access to protected class Y not permitted because enclosing package p
+   |                   is not a subclass of object X in package p where target is defined

tests/neg/i7709.scala

@@ -3,10 +3,29 @@ object X:
   protected class Y
 object A:
   class B extends X.Y // error
+  class B2 extends X.Y: // error
+    def this(n: Int) = this()
+  class B3(x: Any)
+  class B4 extends B3(new X.Y) // error
+  class B5(x: String):
+    def this(n: Int) = this(new X.Y().toString) // error
+trait T:
+  class B extends X.Y // error
 class XX:
   protected class Y
 class C:
   def xx = new XX
   def y  = new xx.Y  // error
+class D:
+  def this(n: Int) = {
+    this()
+    def xx = new XX
+    def y  = new xx.Y  // error
+  }
 class YY extends XX:
   def y = new Y
+
+package p:
+  object X:
+    protected class Y
+  class Q extends X.Y // error