Only check last position, use DoubleDefinition

Author: som-snytt

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

@@ -234,22 +234,6 @@ object Decorators {
     def nestedExists(p: T => Boolean): Boolean = xss match
       case xs :: xss1 => xs.exists(p) || xss1.nestedExists(p)
       case nil => false
-    def nestedZipExists(yss: List[List[U]])(f: (T, U) => Boolean): Boolean =
-      @tailrec def zipExists(p1: List[T], p2: List[U]): Boolean =
-        p1 match
-          case h :: t =>
-            p2 match
-              case h2 :: t2 => f(h, h2) || zipExists(t, t2)
-              case _ => false
-          case _ => false
-      @tailrec def loop(ps1: List[List[T]], ps2: List[List[U]]): Boolean =
-        ps1 match
-          case h :: t =>
-            ps2 match
-              case h2 :: t2 => zipExists(h, h2) || loop(t, t2)
-              case _ => false
-          case _ => false
-      loop(xss, yss)
   end extension
 
   extension (text: Text)

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

@@ -125,7 +125,7 @@ object ErrorReporting {
     /** Explain info of symbol `sym` as a member of class `base`.
      *   @param  showLocation  if true also show sym's location.
      */
-    def infoString(sym: Symbol, base: Type, showLocation: Boolean): String = atPhase(Phases.typerPhase) {
+    def infoString(sym: Symbol, base: Type, showLocation: Boolean): String =
       val sym1 = sym.underlyingSymbol
       def info = base.memberInfo(sym1)
       val infoStr =
@@ -135,7 +135,6 @@ object ErrorReporting {
         else if sym1.isTerm then i" of type $info"
         else ""
       i"${if showLocation then sym1.showLocated else sym1}$infoStr"
-    }
 
     def infoStringWithLocation(sym: Symbol, base: Type) =
       infoString(sym, base, showLocation = true)

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

@@ -336,10 +336,21 @@ object RefChecks {
         next == other || isInheritedAccessor(next, other)
       }
 
+    /** Detect any param section where params in last position do not agree isRepeatedParam.
+     */
     def incompatibleRepeatedParam(member: Symbol, other: Symbol): Boolean =
-      member.is(Method, butNot = JavaDefined) && other.is(Method, butNot = JavaDefined) && atPhase(typerPhase) {
-        member.info.paramInfoss.nestedZipExists(other.info.paramInfoss)(_.isRepeatedParam != _.isRepeatedParam)
-      }
+      def loop(mParamInfoss: List[List[Type]], oParamInfoss: List[List[Type]]): Boolean =
+        mParamInfoss match
+          case Nil => false
+          case h :: t =>
+            oParamInfoss match
+              case Nil => false
+              case h2 :: t2 => h.nonEmpty && h2.nonEmpty && h.last.isRepeatedParam != h2.last.isRepeatedParam
+                            || loop(t, t2)
+      member.is(Method, butNot = JavaDefined)
+      && other.is(Method, butNot = JavaDefined)
+      && atPhase(typerPhase):
+        loop(member.info.paramInfoss, other.info.paramInfoss)
 
     /* Check that all conditions for overriding `other` by `member`
      * of class `clazz` are met.
@@ -502,7 +513,7 @@ object RefChecks {
         else if member.is(Exported) then
           overrideError("cannot override since it comes from an export")
         else if incompatibleRepeatedParam(member, other) then
-          overrideError("cannot override because erased signatures conflict in repeated parameter")
+          report.error(DoubleDefinition(member, other, clazz), member.srcPos)
         else
           overrideError("needs `override` modifier")
       else if (other.is(AbsOverride) && other.isIncompleteIn(clazz) && !member.is(AbsOverride))