Improve error message for inaccessible protected members

Author: nicolasstucki

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

@@ -915,17 +915,17 @@ object SymDenotations {
             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"""
-                 | Access to protected $this not permitted because enclosing ${encl.showLocated}
-                 | is not a subclass of ${owner.showLocated} where target is defined""")
+                | Protected $this can only be accessed from $location.""")
         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
+          val location = if cls.is(Final) then cls.showLocated else cls.showLocated + " or one of its subclasses"
           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""")
+               | Protected $this can only be accessed from $location.""")
       end isProtectedAccessOK
 
       if pre eq NoPrefix then true

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -1123,7 +1123,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         nameString(sym)
 
     if sym.is(ModuleClass) && sym.isTopLevelDefinitionsObject then
-      "top-level definition in package " + nameString(sym.owner.name)
+      "the top-level definitions in package " + nameString(sym.owner.name)
     else (keywordText(kindString(sym)) ~~ {
       if (sym.isAnonymousClass)
         toTextParents(sym.info.parents) ~~ "{...}"

tests/neg-macros/annot-result-owner.check

@@ -2,7 +2,7 @@
 -- Error: tests/neg-macros/annot-result-owner/Test_2.scala:1:0 ---------------------------------------------------------
 1 |@insertVal // error
   |^^^^^^^^^^
-  |macro annotation @insertVal added value definitionWithWrongOwner$macro$1 with an inconsistent owner. Expected it to be owned by top-level definition in package <empty> but was owned by method foo.
+  |macro annotation @insertVal added value definitionWithWrongOwner$macro$1 with an inconsistent owner. Expected it to be owned by the top-level definitions in package <empty> but was owned by method foo.
 -- Error: tests/neg-macros/annot-result-owner/Test_2.scala:5:2 ---------------------------------------------------------
 5 |  @insertVal // error
   |  ^^^^^^^^^^

tests/neg/i12573.check

@@ -4,6 +4,5 @@
    |value getDFType is not a member of DFBits[(8 : Int)].
    |Extension methods were tried, but the search failed with:
    |
-   |    method getDFType cannot be accessed as a member of DFType.type from top-level definition in package <empty>.
-   |     Access to protected method getDFType not permitted because enclosing top-level definition in package <empty>
-   |     is not a subclass of object DFType where target is defined
+   |    method getDFType cannot be accessed as a member of DFType.type from the top-level definitions in package <empty>.
+   |     Protected method getDFType can only be accessed from object DFType.

tests/neg/i7709.check

@@ -2,47 +2,39 @@
 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
+  |                   Protected class Y can only be accessed from object X.
 -- [E173] Reference 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
+  |                    Protected class Y can only be accessed from object X.
 -- [E173] Reference 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
+  |                           Protected class Y can only be accessed from object X.
 -- [E173] Reference 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
+   |                                 Protected class Y can only be accessed from object X.
 -- [E173] Reference 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
+   |                   Protected class Y can only be accessed from object X.
 -- [E173] Reference 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
+   |                Protected class Y can only be accessed from class XX or one of its subclasses.
 -- [E173] Reference 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
+   |                  Protected class Y can only be accessed from class XX or one of its subclasses.
 -- [E173] Reference 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
+   |                   Protected class Y can only be accessed from object X in package p.

tests/neg/not-accessible.check

@@ -9,12 +9,12 @@
 -- [E173] Reference Error: tests/neg/not-accessible.scala:13:23 --------------------------------------------------------
 13 |    def test(a: A) = a.x // error
    |                     ^^^
-   |                 value x cannot be accessed as a member of (a : foo.A) from top-level definition in package bar.
+   |            value x cannot be accessed as a member of (a : foo.A) from the top-level definitions in package bar.
 -- [E173] Reference Error: tests/neg/not-accessible.scala:5:21 ---------------------------------------------------------
 5 |  def test(a: A) = a.x // error
   |                   ^^^
-  |                   value x cannot be accessed as a member of (a : foo.A) from top-level definition in package foo.
+  |              value x cannot be accessed as a member of (a : foo.A) from the top-level definitions in package foo.
 -- [E173] Reference Error: tests/neg/not-accessible.scala:15:23 --------------------------------------------------------
 15 |def test(a: foo.A) = a.x // error
    |                     ^^^
-   |             value x cannot be accessed as a member of (a : foo.A) from top-level definition in package <empty>.
+   |        value x cannot be accessed as a member of (a : foo.A) from the top-level definitions in package <empty>.