Ignore override errors in EqClass

These clash with final members in Any, but that's OK.

Author: odersky

src/dotty/tools/dotc/typer/RefChecks.scala

@@ -300,7 +300,7 @@ object RefChecks {
         overrideError("cannot be used here - class definitions cannot be overridden")
       } else if (!other.is(Deferred) && member.isClass) {
         overrideError("cannot be used here - classes can only override abstract types")
-      } else if (other.isEffectivelyFinal) { // (1.2)
+      } else if (other.isEffectivelyFinal && !isIgnorable(member)) { // (1.2)
         overrideError(i"cannot override final member ${other.showLocated}")
       } else if (!other.is(Deferred) &&
                  !isDefaultGetter(other.name) &&
@@ -314,7 +314,7 @@ object RefChecks {
             clazz + " inherits conflicting members:\n  "
               + infoStringWithLocation(other) + "  and\n  " + infoStringWithLocation(member)
               + "\n(Note: this can be resolved by declaring an override in " + clazz + ".)")
-        else
+        else if (!isIgnorable(member))
           overrideError("needs `override' modifier")
       } else if (other.is(AbsOverride) && other.isIncompleteIn(clazz) && !member.is(AbsOverride)) {
         overrideError("needs `abstract override' modifiers")
@@ -640,6 +640,13 @@ object RefChecks {
       }
   }
 
+  /** Ignore `==' entries in EqClass; they clash with `final` entries in `Any` */
+  private def isIgnorable(sym: Symbol)(implicit ctx: Context) = {
+    val res = sym.owner == defn.EqClassClass
+    if (!res) println(i"not ignorable: ${sym.owner} / ${defn.EqClassClass}")
+    res
+  }
+
   // Note: if a symbol has both @deprecated and @migration annotations and both
   // warnings are enabled, only the first one checked here will be emitted.
   // I assume that's a consequence of some code trying to avoid noise by suppressing