Refactor CannotBeAccessed/isAccessibleFrom

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

@@ -877,7 +877,7 @@ object SymDenotations {
      *  As a side effect, drop Local flags of members that are not accessed via the ThisType
      *  of their owner.
      */
-    final def isAccessibleFrom(pre: Type, superAccess: Boolean = false, whyNot: StringBuffer | Null = null)(using Context): Boolean = {
+    final def isAccessibleFrom(pre: Type, superAccess: Boolean = false)(using Context): Boolean = {
 
       /** Are we inside definition of `boundary`?
        *  If this symbol is Java defined, package structure is interpreted to be flat.
@@ -906,26 +906,13 @@ object SymDenotations {
 
       /** Is protected access to target symbol permitted? */
       def isProtectedAccessOK: Boolean =
-        inline def fail(str: String): false =
-          if whyNot != null then whyNot.nn.append(str)
-          false
         val cls = owner.enclosingSubClass
         if !cls.exists then
-          if pre.termSymbol.isPackageObject && accessWithin(pre.termSymbol.owner) then
-            true
-          else
-            val encl = if ctx.owner.isConstructor then ctx.owner.enclosingClass.owner.enclosingClass else ctx.owner.enclosingClass
-            val location = if owner.is(Final) then owner.showLocated else owner.showLocated + " or one of its subclasses"
-            fail(i"""
-                | Protected $this can only be accessed from $location.""")
-        else if isType || pre.derivesFrom(cls) || isConstructor || owner.is(ModuleClass) then
+          pre.termSymbol.isPackageObject && accessWithin(pre.termSymbol.owner)
+        else
           // allow accesses to types from arbitrary subclasses fixes #4737
           // don't perform this check for static members
-          true
-        else
-          val location = if cls.is(Final) then cls.showLocated else cls.showLocated + " or one of its subclasses"
-          fail(i"""
-               | Protected $this can only be accessed from $location.""")
+          isType || pre.derivesFrom(cls) || isConstructor || owner.is(ModuleClass)
       end isProtectedAccessOK
 
       if pre eq NoPrefix then true

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -876,7 +876,7 @@ extends Message(PatternMatchExhaustivityID) {
 
     val pathes = List(
       ActionPatch(
-        srcPos = endPos, 
+        srcPos = endPos,
         replacement = uncoveredCases.map(c => indent(s"case $c => ???", startColumn))
           .mkString("\n", "\n", "")
       ),
@@ -2986,7 +2986,13 @@ extends ReferenceMsg(CannotBeAccessedID):
         i"none of the overloaded alternatives named $name can"
     val where = if (ctx.owner.exists) i" from ${ctx.owner.enclosingClass}" else ""
     val whyNot = new StringBuffer
-    alts.foreach(_.isAccessibleFrom(pre, superAccess, whyNot))
+    for alt <- alts do
+      if alt.is(Protected) then
+        val cls = alt.owner.enclosingSubClass
+        val owner = if cls.exists then cls else alt.owner
+        val location = if owner.is(Final) then owner.showLocated else owner.showLocated + " or one of its subclasses"
+        whyNot.append(i"""
+            | Protected $alt can only be accessed from $location.""")
     i"$whatCanNot be accessed as a member of $pre$where.$whyNot"
   def explain(using Context) = ""
 

tests/neg/i18686.check

@@ -0,0 +1,13 @@
+-- [E173] Reference Error: tests/neg/i18686.scala:9:16 -----------------------------------------------------------------
+9 |    println(Foo.Bar1) // error
+  |            ^^^^^^^^
+  |            value Bar1 cannot be accessed as a member of Foo.type from object Main.
+-- [E173] Reference Error: tests/neg/i18686.scala:10:16 ----------------------------------------------------------------
+10 |    println(Foo.Bar2) // error
+   |            ^^^^^^^^
+   |            value Bar2 cannot be accessed as a member of Foo.type from object Main.
+-- [E173] Reference Error: tests/neg/i18686.scala:11:16 ----------------------------------------------------------------
+11 |    println(Foo.Bar3) // error
+   |            ^^^^^^^^
+   |            value Bar3 cannot be accessed as a member of Foo.type from object Main.
+   |             Protected value Bar3 can only be accessed from object Foo.

tests/neg/i18686.scala

@@ -0,0 +1,13 @@
+object Foo:
+  private val Bar1: Int = 3
+  private[Foo] val Bar2: Int = 3
+  protected val Bar3: Int = 3
+end Foo
+
+object Main:
+  def main(args: Array[String]): Unit =
+    println(Foo.Bar1) // error
+    println(Foo.Bar2) // error
+    println(Foo.Bar3) // error
+  end main
+end Main