Constructor companion gets privateWithin (#22627)

Follow-up to #22560 
Fixes #22626 

When creating a companion for a constructor proxy, the companion is
`protected` if the class is. Now it also receives the `privateWithin`
boundary of the class, for `protected[p]`.

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

@@ -183,8 +183,9 @@ object NamerOps:
         cls.owner, cls.name.toTermName,
         flags, flags,
         constructorCompanionCompleter(cls),
-        coord = cls.coord,
-        compUnitInfo = cls.compUnitInfo)
+        cls.privateWithin,
+        cls.coord,
+        cls.compUnitInfo)
     companion.moduleClass.registerCompanion(cls)
     cls.registerCompanion(companion.moduleClass)
     companion

tests/neg/i18545.check

@@ -1,16 +1,26 @@
--- [E173] Reference Error: tests/neg/i18545.scala:13:20 ----------------------------------------------------------------
-13 |  def test: IOLocal.IOLocalImpl[Int] = // error
+-- [E173] Reference Error: tests/neg/i18545.scala:16:20 ----------------------------------------------------------------
+16 |  def test: IOLocal.IOLocalImpl[Int] = // error
    |            ^^^^^^^^^^^^^^^^^^^
    |class IOLocalImpl cannot be accessed as a member of iolib.IOLocal.type from the top-level definitions in package tests.
    |  private[IOLocal] class IOLocalImpl can only be accessed from object IOLocal in package iolib.
--- [E173] Reference Error: tests/neg/i18545.scala:14:24 ----------------------------------------------------------------
-14 |    IOLocal.IOLocalImpl.apply(42) // error
+-- [E173] Reference Error: tests/neg/i18545.scala:17:24 ----------------------------------------------------------------
+17 |    IOLocal.IOLocalImpl.apply(42) // error
    |    ^^^^^^^^^^^^^^^^^^^^^^^^^
    |method apply cannot be accessed as a member of iolib.IOLocal.IOLocalImpl.type from the top-level definitions in package tests.
    |  private[IOLocal] method apply can only be accessed from object IOLocal in package iolib.
--- [E050] Type Error: tests/neg/i18545.scala:15:22 ---------------------------------------------------------------------
-15 |  def test2 = IOLocal.IOLocalImpl(42) // error
+-- [E050] Type Error: tests/neg/i18545.scala:18:22 ---------------------------------------------------------------------
+18 |  def test2 = IOLocal.IOLocalImpl(42) // error
    |              ^^^^^^^^^^^^^^^^^^^
    |              object IOLocalImpl in object IOLocal does not take parameters
    |
    | longer explanation available when compiling with `-explain`
+-- [E173] Reference Error: tests/neg/i18545.scala:19:22 ----------------------------------------------------------------
+19 |  def test3 = IOLocal.AltIOLocalImpl.apply(42) // error
+   |              ^^^^^^^^^^^^^^^^^^^^^^
+   |object AltIOLocalImpl cannot be accessed as a member of iolib.IOLocal.type from the top-level definitions in package tests.
+   |  private[IOLocal] object AltIOLocalImpl can only be accessed from object IOLocal in package iolib.
+-- [E173] Reference Error: tests/neg/i18545.scala:20:22 ----------------------------------------------------------------
+20 |  def test4 = IOLocal.AltIOLocalImpl(42) // error
+   |              ^^^^^^^^^^^^^^^^^^^^^^
+   |object AltIOLocalImpl cannot be accessed as a member of iolib.IOLocal.type from the top-level definitions in package tests.
+   |  private[IOLocal] object AltIOLocalImpl can only be accessed from object IOLocal in package iolib.

tests/neg/i18545.scala

@@ -7,9 +7,14 @@ package iolib:
     def apply[A](default: A): IO[IOLocal[A]] = IO(new IOLocalImpl(default))
 
     private[IOLocal] final class IOLocalImpl[A](default: A) extends IOLocal[A]
+    object IOLocalImpl
+
+    private[IOLocal] final class AltIOLocalImpl[A](default: A) extends IOLocal[A]
 
 package tests:
   import iolib.IOLocal
   def test: IOLocal.IOLocalImpl[Int] = // error
     IOLocal.IOLocalImpl.apply(42) // error
   def test2 = IOLocal.IOLocalImpl(42) // error
+  def test3 = IOLocal.AltIOLocalImpl.apply(42) // error
+  def test4 = IOLocal.AltIOLocalImpl(42) // error

tests/neg/i22560b.scala

@@ -12,7 +12,9 @@ package p:
   private[p] class C(i: Int) // ctor proxy gets privateWithin of class
   private[p] class D(i: Int)
   object D
+  private class E(i: Int)
 
 package q:
   def f() = p.C(42) // error
   def g() = p.D(42) // error
+  def h() = p.E(42) // error

tests/neg/i22560c/client_2.scala

@@ -0,0 +1,11 @@
+
+package i22560:
+  val alpha = C.D() // error
+
+  class Test extends Enumeration:
+    val Hearts = Val(27) // error
+    val Diamonds = Val() // error
+
+package q:
+  def f() = p.C(42) // error
+  def g() = p.D(42) // error

tests/neg/i22560c/lib_1.scala

@@ -0,0 +1,16 @@
+
+package i22560:
+
+  object C:
+    protected class D
+
+  class Enumeration:
+    protected class Val(i: Int):
+      def this() = this(42)
+    object Val
+
+package p:
+  private[p] class C(i: Int) // companion gets privateWithin of class
+  private[p] class D(i: Int) // ctor proxy gets privateWithin of class
+  object D
+

tests/pos/i22560.scala

@@ -20,3 +20,13 @@ package companioned:
   class Test extends Enumeration:
     val Hearts = Val(27)
     val Diamonds = Val()
+
+package p:
+
+  package internal:
+
+    protected[p] class P(i : Int)
+    private[p] class Q(i : Int)
+
+  def f = internal.P(42)
+  def g = internal.Q(42)

tests/pos/i22560b/client_2.scala

@@ -0,0 +1,17 @@
+
+package companionless:
+
+  class Test extends Enumeration:
+    val Hearts = Val(27)
+    val Diamonds = Val()
+
+
+package companioned:
+
+  class Test extends Enumeration:
+    val Hearts = Val(27)
+    val Diamonds = Val()
+
+package p:
+
+  def f = internal.P(42)

tests/pos/i22560b/lib_1.scala

@@ -0,0 +1,19 @@
+
+package companionless:
+
+  class Enumeration:
+    protected class Val(i: Int):
+      def this() = this(42)
+
+package companioned:
+
+  class Enumeration:
+    protected class Val(i: Int):
+      def this() = this(42)
+    protected object Val
+
+package p:
+
+  package internal:
+
+    protected[p] class P(i : Int)