Context for constructor error is outer context

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

@@ -824,30 +824,25 @@ object SymDenotations {
       }
 
       /** Is protected access to target symbol permitted? */
-      def isProtectedAccessOK = {
-        def fail(str: => String): Boolean = {
-          if (whyNot != null) whyNot append str
+      def isProtectedAccessOK: Boolean =
+        inline def fail(str: String): false =
+          if whyNot != null then whyNot.append(str)
           false
-        }
         val cls = owner.enclosingSubClass
-        if (!cls.exists)
-          fail(
-            i"""
-               | Access to protected $this not permitted because enclosing ${ctx.owner.enclosingClass.showLocated}
+        if !cls.exists then
+          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
       else if isAbsent() then false

tests/neg/i7709.check

@@ -0,0 +1,48 @@
+-- Error: tests/neg/i7709.scala:5:20 -----------------------------------------------------------------------------------
+5 |  class B extends X.Y // error
+  |                  ^^^
+  |                  class Y 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:6:21 -----------------------------------------------------------------------------------
+6 |  class B2 extends X.Y: // error
+  |                   ^^^
+  |                   class Y 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 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 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 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 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

@@ -0,0 +1,31 @@
+
+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