Change 'overrides nothing' to report via Message (see #1965) (#1968)

* Change 'overrides nothing' to report via Message, split into two different messages

* Change 'overrides nothing' to report via Message, split into two different messages

2 files changed, 38 insertions, 6 deletions

diff --git a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
index 89cd2cd8f..c25c49597 100644
--- a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
@@ -1002,4 +1002,36 @@ object messages {
            |${typeCode}
            |"""
   }
+
+  case class OverridesNothing(member: Symbol)(implicit ctx: Context)
+  extends Message(37) {
+    val kind = "Reference"
+    val msg = hl"""${member} overrides nothing"""
+
+    val explanation =
+      hl"""|There must be a field or method with the name `${member.name}` in a super
+           |class of `${member.owner}` to override it. Did you misspell it?
+           |Are you extending the right classes?
+           |"""
+  }
+
+  case class OverridesNothingButNameExists(member: Symbol, existing: List[Denotations.SingleDenotation])(implicit ctx: Context)
+  extends Message(38) {
+    val kind = "Reference"
+    val msg = hl"""${member} has a different signature than the overridden declaration"""
+
+    val existingDecl = existing.map(_.showDcl).mkString("  \n")
+
+    val explanation =
+      hl"""|There must be a non-final field or method with the name `${member.name}` and the
+           |same parameter list in a super class of `${member.owner}` to override it.
+           |
+           |  ${member.showDcl}
+           |
+           |The super classes of `${member.owner}` contain the following members
+           |named `${member.name}`:
+           |  ${existingDecl}
+           |"""
+  }
+
 }
diff --git a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
index e113399c5..ada53047a 100644
--- a/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/compiler/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -21,6 +21,9 @@ import DenotTransformers._
 
 object RefChecks {
   import tpd._
+  import reporting.diagnostic.Message
+  import reporting.diagnostic.messages._
+
 
   private def isDefaultGetter(name: Name): Boolean =
     name.isTermName && name.asTermName.defaultGetterIndex >= 0
@@ -622,15 +625,12 @@ object RefChecks {
       if (member.isAnyOverride && !(clazz.thisType.baseClasses exists (hasMatchingSym(_, member)))) {
         // for (bc <- clazz.info.baseClasses.tail) Console.println("" + bc + " has " + bc.info.decl(member.name) + ":" + bc.info.decl(member.name).tpe);//DEBUG
 
-        val nonMatching = clazz.info.member(member.name).altsWith(alt => alt.owner != clazz && !alt.is(Final))
-        def issueError(suffix: String) =
-          ctx.error(i"$member overrides nothing$suffix", member.pos)
+        val nonMatching = clazz.info.member(member.name).altsWith(alt => alt.owner != clazz)
         nonMatching match {
           case Nil =>
-            issueError("")
+            ctx.error(OverridesNothing(member), member.pos)
           case ms =>
-            val superSigs = ms.map(_.showDcl).mkString("\n")
-            issueError(s".\nNote: the super classes of ${member.owner} contain the following, non final members named ${member.name}:\n${superSigs}")
+            ctx.error(OverridesNothingButNameExists(member, ms), member.pos)
         }
         member.resetFlag(Override)
         member.resetFlag(AbsOverride)