address review feedback

Author: liufengyun

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -791,9 +791,9 @@ object messages {
 
     val explanation =
       hl"""|There are several ways to make the match exhaustive:
-           | - add missing cases as shown in the warning
-           | - change the return type of irrefutable extractors as `Some[T]` if exist
-           | - add a wildcard `_` case at the end
+           | - Add missing cases as shown in the warning
+           | - If an extractor always return Some(...), write Some[X] for its return type
+           | - Add a case _ => ... at the end to match all remaining cases
            |"""
   }
 

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -641,6 +641,14 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
 
   /** Display spaces */
   def show(s: Space): String = {
+
+    // does the companion object of the given symbol have custom unapply
+    def hasCustomUnapply(sym: Symbol): Boolean = {
+      val companion = sym.companionModule
+      companion.findMember(nme.unapply, NoPrefix, Flags.Synthetic).exists ||
+        companion.findMember(nme.unapplySeq, NoPrefix, Flags.Synthetic).exists
+    }
+
     def doShow(s: Space, mergeList: Boolean = false): String = s match {
       case Empty => ""
       case Typ(c: ConstantType, _) => c.value.show
@@ -654,11 +662,9 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
           if (mergeList) "_*" else "_: List"
         else if (scalaConsType.isRef(sym))
           if (mergeList) "_" else "List(_)"
-        else if (tp.classSymbol.is(CaseClass))
+        else if (tp.classSymbol.is(CaseClass) && !hasCustomUnapply(tp.classSymbol))
         // use constructor syntax for case class
           showType(tp) + signature(tp).map(_ => "_").mkString("(", ", ", ")")
-        else if (sym.is(Flags.Case) && signature(tp).nonEmpty)
-          tp.classSymbol.name + signature(tp).map(_ => "_").mkString("(", ", ", ")")
         else if (decomposed) "_: " + showType(tp)
         else "_"
       case Kon(tp, params) =>

tests/patmat/i2502b.check

@@ -0,0 +1 @@
+5: Pattern Match Exhaustivity: _: BTypes.ClassBType

tests/patmat/i2502b.scala

@@ -0,0 +1,17 @@
+abstract class BTypes {
+  trait BType
+
+  sealed trait RefBType extends BType {
+    def classOrArrayType: String = this match {
+      case ClassBType(internalName) => internalName
+      case a: ArrayBType            => ""
+    }
+  }
+
+  final case class ClassBType(val internalName: String) extends RefBType
+  class ArrayBType extends RefBType
+
+  object ClassBType {
+    def unapply(x: RefBType): Option[String] = None
+  }
+}