Fix #2631: Add custom error message

Author: nicolasstucki

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

@@ -396,6 +396,8 @@ class Typer extends Namer
       }
       else if (name.toTermName == nme.ERROR)
         UnspecifiedErrorType
+      else if (ctx.owner.isConstructor && ctx.owner.owner.unforcedDecls.toList.exists(_.name == tree.name))
+        errorType(ex"$tree is not accessible from super constructor arguments", tree.pos)
       else
         errorType(new MissingIdent(tree, kind, name.show), tree.pos)
 

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 super constructor arguments