Check exhaustivity of any case class (#22604)

Fixes #22590

Author: dwijnand

Diff for: compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala

@@ -169,7 +169,7 @@ trait BCodeSkelBuilder extends BCodeHelpers {
 
     /* ---------------- helper utils for generating classes and fields ---------------- */
 
-    def genPlainClass(cd0: TypeDef) = cd0 match {
+    def genPlainClass(cd0: TypeDef) = (cd0: @unchecked) match {
       case TypeDef(_, impl: Template) =>
       assert(cnode == null, "GenBCode detected nested methods.")
 

Diff for: compiler/src/dotty/tools/dotc/core/Comments.scala

@@ -405,15 +405,10 @@ object Comments {
       val Trim = "(?s)^[\\s&&[^\n\r]]*(.*?)\\s*$".r
 
       val raw = ctx.docCtx.flatMap(_.docstring(sym).map(_.raw)).getOrElse("")
-      defs(sym) ++= defines(raw).map {
-        str => {
-          val start = skipWhitespace(str, "@define".length)
-          val (key, value) = str.splitAt(skipVariable(str, start))
-          key.drop(start) -> value
-        }
-      } map {
-        case (key, Trim(value)) =>
-          variableName(key) -> value.replaceAll("\\s+\\*+$", "")
+      defs(sym) ++= defines(raw).map { str =>
+        val start = skipWhitespace(str, "@define".length)
+        val (key, Trim(value)) = str.splitAt(skipVariable(str, start)): @unchecked
+        variableName(key.drop(start)) -> value.replaceAll("\\s+\\*+$", "")
       }
     }
 

Diff for: 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)

Diff for: compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -1383,30 +1383,31 @@ trait Implicits:
             if alt1.isExtension then
               // Fall back: if both results are extension method applications,
               // compare the extension methods instead of their wrappers.
-              def stripExtension(alt: SearchSuccess) = methPart(stripApply(alt.tree)).tpe
-              (stripExtension(alt1), stripExtension(alt2)) match
-                case (ref1: TermRef, ref2: TermRef) =>
-                  // ref1 and ref2 might refer to type variables owned by
-                  // alt1.tstate and alt2.tstate respectively, to compare the
-                  // alternatives correctly we need a TyperState that includes
-                  // constraints from both sides, see
-                  // tests/*/extension-specificity2.scala for test cases.
-                  val constraintsIn1 = alt1.tstate.constraint ne ctx.typerState.constraint
-                  val constraintsIn2 = alt2.tstate.constraint ne ctx.typerState.constraint
-                  def exploreState(alt: SearchSuccess): TyperState =
-                    alt.tstate.fresh(committable = false)
-                  val comparisonState =
-                    if constraintsIn1 && constraintsIn2 then
-                      exploreState(alt1).mergeConstraintWith(alt2.tstate)
-                    else if constraintsIn1 then
-                      exploreState(alt1)
-                    else if constraintsIn2 then
-                      exploreState(alt2)
-                    else
-                      ctx.typerState
-
-                  diff = inContext(searchContext().withTyperState(comparisonState)):
-                    compare(ref1, ref2, preferGeneral = true)
+              def stripExtension(alt: SearchSuccess) =
+                methPart(stripApply(alt.tree)).tpe: @unchecked match { case ref: TermRef => ref }
+              val ref1 = stripExtension(alt1)
+              val ref2 = stripExtension(alt2)
+              // ref1 and ref2 might refer to type variables owned by
+              // alt1.tstate and alt2.tstate respectively, to compare the
+              // alternatives correctly we need a TyperState that includes
+              // constraints from both sides, see
+              // tests/*/extension-specificity2.scala for test cases.
+              val constraintsIn1 = alt1.tstate.constraint ne ctx.typerState.constraint
+              val constraintsIn2 = alt2.tstate.constraint ne ctx.typerState.constraint
+              def exploreState(alt: SearchSuccess): TyperState =
+                alt.tstate.fresh(committable = false)
+              val comparisonState =
+                if constraintsIn1 && constraintsIn2 then
+                  exploreState(alt1).mergeConstraintWith(alt2.tstate)
+                else if constraintsIn1 then
+                  exploreState(alt1)
+                else if constraintsIn2 then
+                  exploreState(alt2)
+                else
+                  ctx.typerState
+
+              diff = inContext(searchContext().withTyperState(comparisonState)):
+                compare(ref1, ref2, preferGeneral = true)
             else // alt1 is a conversion, prefer extension alt2 over it
               diff = -1
           if diff < 0 then alt2

Diff for: scaladoc/src/dotty/tools/scaladoc/site/templates.scala

@@ -102,11 +102,9 @@ case class TemplateFile(
       ctx.layouts.getOrElse(name, throw new RuntimeException(s"No layouts named $name in ${ctx.layouts}"))
     )
 
-    def asJavaElement(o: Object): Object = o match
-      case m: Map[?, ?] => m.transform {
-        case (k: String, v: Object) => asJavaElement(v)
-      }.asJava
-      case l: List[?] => l.map(x => asJavaElement(x.asInstanceOf[Object])).asJava
+    def asJavaElement(o: Any): Any = o match
+      case m: Map[?, ?] => m.transform { (k, v) => asJavaElement(v) }.asJava
+      case l: List[?] => l.map(asJavaElement).asJava
       case other => other
 
     // Library requires mutable maps..

Diff for: tests/pos/switches.scala

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

Diff for: 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 =

Diff for: tests/warn/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 { // warn: match may not be exhaustive.
+    case CC_B(12, CC_A()) => 0
+    case CC_B(_, CC_C()) => 0
+  }
+}

Diff for: tests/warn/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{ // warn: match may not be exhaustive.
+    case CC_B(12) => 0
+  }
+}

Diff for: 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

Diff for: 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