Check exhaustivity of any case class

Author: dwijnand

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

@@ -841,8 +841,6 @@ object SpaceEngine {
     if Nullables.unsafeNullsEnabled then self.stripNull() else self
 
   private def exhaustivityCheckable(sel: Tree)(using Context): Boolean = trace(i"exhaustivityCheckable($sel ${sel.className})") {
-    val seen = collection.mutable.Set.empty[Symbol]
-
     // Possible to check everything, but be compatible with scalac by default
     def isCheckable(tp: Type): Boolean = trace(i"isCheckable($tp ${tp.className})"):
       val tpw = tp.widen.dealias.stripUnsafeNulls()
@@ -856,10 +854,7 @@ object SpaceEngine {
       }) ||
       tpw.isRef(defn.BooleanClass) ||
       classSym.isAllOf(JavaEnum) ||
-      classSym.is(Case) && {
-        if seen.add(classSym) then productSelectorTypes(tpw, sel.srcPos).exists(isCheckable(_))
-        else true // recursive case class: return true and other members can still fail the check
-      }
+      classSym.is(Case)
 
     !sel.tpe.hasAnnotation(defn.UncheckedAnnot)
     && !sel.tpe.hasAnnotation(defn.RuntimeCheckedAnnot)

i22590.arity2.scala

@@ -0,0 +1,15 @@
+sealed trait T_B
+case class CC_A() extends T_B
+case class CC_C() extends T_B
+
+sealed trait T_A
+case class CC_B[B](a: B,b:T_B) extends T_A
+
+
+@main def test() = {
+  val v_a: CC_B[Int] = null
+  val v_b: Int = v_a match {
+    case CC_B(12, CC_A()) => 0
+    case CC_B(_, CC_C()) => 0
+  }
+}

i22590.scala

@@ -0,0 +1,9 @@
+sealed trait T_A
+case class CC_B[T](a: T) extends T_A
+
+@main def test() = {
+  val v_a: CC_B[Int] = CC_B(10)
+  val v_b: Int = v_a match{
+    case CC_B(12) => 0
+  }
+}

tests/pos/switches.scala

@@ -42,6 +42,7 @@ class Test {
     case IntAnyVal(100) => 2
     case IntAnyVal(1000) => 3
     case IntAnyVal(10000) => 4
+    case _ => -1
   }
 }
 

tests/warn/i15662.scala

@@ -5,6 +5,7 @@ case class Composite[T](v: T)
 def m(composite: Composite[?]): Unit =
   composite match {
     case Composite[Int](v) => println(v)  // warn: cannot be checked at runtime
+    case _ => println("OTHER")
   }
 
 def m2(composite: Composite[?]): Unit =

tests/warn/opaque-match.scala

@@ -13,8 +13,10 @@ def Test[T] =
     case _: C => ???   // ok
   C() match
     case _: O.T => ???  // warn
+    case _ => ???
   C() match
     case _: T => ???   // warn
+    case _ => ???
 
   (??? : Any) match
     case _: List[O.T] => ???  // warn

tests/pos/t10373.scala renamed to tests/warn/t10373.scala

@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -deprecation -feature
 
 abstract class Foo {
   def bar(): Unit = this match {
@@ -7,7 +7,7 @@ abstract class Foo {
                     // Works fine
   }
 
-  def baz(that: Foo): Unit = (this, that) match {
+  def baz(that: Foo): Unit = (this, that) match { // warn: match may not be exhaustive.
     case (Foo_1(), _) => //do something
     case (Foo_2(), _) => //do something
                          // match may not be exhaustive