Merge pull request scala#3802 from dotty-staging/fix-#2631

Fix scala#2631: Add custom error message

Author: nicolasstucki

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -396,7 +396,12 @@ class Typer extends Namer
       }
       else if (name.toTermName == nme.ERROR)
         UnspecifiedErrorType
-      else
+      else if (ctx.owner.isConstructor && ctx.mode.is(Mode.InSuperCall) &&
+          ctx.owner.owner.unforcedDecls.lookup(tree.name).exists) {
+        // When InSuperCall mode and in a constructor we are in the arguments
+        // of a this(...) constructor call
+        errorType(ex"$tree is not accessible from constructor arguments", tree.pos)
+      } else
         errorType(new MissingIdent(tree, kind, name.show), tree.pos)
 
     val tree1 = ownType match {

compiler/test-resources/repl/i2631

@@ -0,0 +1,4 @@
+scala> class Foo(x : Any) { val foo : Integer = 0; def this() = { this(foo) } }
+1 | class Foo(x : Any) { val foo : Integer = 0; def this() = { this(foo) } }
+  |                                                                 ^^^
+  |                          foo is not accessible from constructor arguments