Merge pull request #2197 from dotty-staging/add-enum-exhaustiveness

Add enum exhaustivity checking

4 files changed, 77 insertions, 100 deletions

diff --git a/compiler/src/dotty/tools/dotc/config/Printers.scala b/compiler/src/dotty/tools/dotc/config/Printers.scala
index 002d0f933..a77607d18 100644
--- a/compiler/src/dotty/tools/dotc/config/Printers.scala
+++ b/compiler/src/dotty/tools/dotc/config/Printers.scala
@@ -31,4 +31,5 @@ object Printers {
   val cyclicErrors: Printer = noPrinter
   val pickling: Printer = noPrinter
   val inlining: Printer = noPrinter
+  val exhaustivity: Printer = noPrinter
 }
diff --git a/compiler/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala b/compiler/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala
index ebd2ae436..b48d219d6 100644
--- a/compiler/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala
+++ b/compiler/src/dotty/tools/dotc/transform/IsInstanceOfEvaluator.scala
@@ -147,6 +147,9 @@ class IsInstanceOfEvaluator extends MiniPhaseTransform { thisTransformer =>
             (scTrait && selTrait)
 
           val inMatch = s.qualifier.symbol is Case
+            // FIXME: This will misclassify case objects! We need to find another way to characterize
+            // isInstanceOfs generated by matches.
+            // Probably the most robust way is to use another symbol for the isInstanceOf method.
 
           if (valueClassesOrAny) tree
           else if (knownStatically)
diff --git a/compiler/src/dotty/tools/dotc/transform/PostTyper.scala b/compiler/src/dotty/tools/dotc/transform/PostTyper.scala
index 9821757e8..bacb88091 100644
--- a/compiler/src/dotty/tools/dotc/transform/PostTyper.scala
+++ b/compiler/src/dotty/tools/dotc/transform/PostTyper.scala
@@ -104,8 +104,14 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer  { thisTran
     private def transformAnnot(annot: Annotation)(implicit ctx: Context): Annotation =
       annot.derivedAnnotation(transformAnnot(annot.tree))
 
+    private def registerChild(sym: Symbol, tp: Type)(implicit ctx: Context) = {
+      val cls = tp.classSymbol
+      if (cls.is(Sealed)) cls.addAnnotation(Annotation.makeChild(sym))
+    }
+
     private def transformMemberDef(tree: MemberDef)(implicit ctx: Context): Unit = {
       val sym = tree.symbol
+      if (sym.is(CaseVal, butNot = Method | Module)) registerChild(sym, sym.info)
       sym.transformAnnotations(transformAnnot)
     }
 
@@ -227,9 +233,9 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer  { thisTran
 
             // Add Child annotation to sealed parents unless current class is anonymous
             if (!sym.isAnonymousClass) // ignore anonymous class
-              for (parent <- sym.asClass.classInfo.classParents) {
-                val pclazz = parent.classSymbol
-                if (pclazz.is(Sealed)) pclazz.addAnnotation(Annotation.makeChild(sym))
+              sym.asClass.classInfo.classParents.foreach { parent =>
+                val sym2 = if (sym.is(Module)) sym.sourceModule else sym
+                registerChild(sym2, parent)
               }
 
             tree
diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
index 8d926fcf0..baf1ae356 100644
--- a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
+++ b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
@@ -13,6 +13,7 @@ import core.StdNames._
 import core.NameOps._
 import core.Constants._
 import reporting.diagnostic.messages._
+import config.Printers.{ exhaustivity => debug }
 
 /** Space logic for checking exhaustivity and unreachability of pattern matching
  *
@@ -28,8 +29,6 @@ import reporting.diagnostic.messages._
  *      3. A union of spaces `S1 | S2 | ...` is a space
  *      4. For a case class Kon(x1: T1, x2: T2, .., xn: Tn), if S1, S2, ..., Sn
  *          are spaces, then `Kon(S1, S2, ..., Sn)` is a space.
- *      5. A constant `Const(value, T)` is a point in space
- *      6. A stable identifier `Var(sym, T)` is a space
  *
  *  For the problem of exhaustivity check, its formulation in terms of space is as follows:
  *
@@ -67,15 +66,6 @@ case class Kon(tp: Type, params: List[Space]) extends Space
 /** Union of spaces */
 case class Or(spaces: List[Space]) extends Space
 
-/** Point in space */
-sealed trait Point extends Space
-
-/** Point representing variables(stable identifier) in patterns */
-case class Var(sym: Symbol, tp: Type) extends Point
-
-/** Point representing literal constants in patterns */
-case class Const(value: Constant, tp: Type) extends Point
-
 /** abstract space logic */
 trait SpaceLogic {
   /** Is `tp1` a subtype of `tp2`? */
@@ -97,6 +87,9 @@ trait SpaceLogic {
   /** Get components of decomposable types */
   def decompose(tp: Type): List[Space]
 
+  /** Display space in string format */
+  def show(sp: Space): String
+
   /** Simplify space using the laws, there's no nested union after simplify */
   def simplify(space: Space): Space = space match {
     case Kon(tp, spaces) =>
@@ -137,7 +130,7 @@ trait SpaceLogic {
     def tryDecompose1(tp: Type) = canDecompose(tp) && isSubspace(Or(decompose(tp)), b)
     def tryDecompose2(tp: Type) = canDecompose(tp) && isSubspace(a, Or(decompose(tp)))
 
-    (a, b) match {
+    val res = (a, b) match {
       case (Empty, _) => true
       case (_, Empty) => false
       case (Or(ss), _) => ss.forall(isSubspace(_, b))
@@ -157,17 +150,11 @@ trait SpaceLogic {
         simplify(minus(a, b)) == Empty
       case (Kon(tp1, ss1), Kon(tp2, ss2)) =>
         isEqualType(tp1, tp2) && ss1.zip(ss2).forall((isSubspace _).tupled)
-      case (Const(v1, _), Const(v2, _)) => v1 == v2
-      case (Const(_, tp1), Typ(tp2, _)) => isSubType(tp1, tp2) || tryDecompose2(tp2)
-      case (Const(_, _), Or(ss)) => ss.exists(isSubspace(a, _))
-      case (Const(_, _), _) => false
-      case (_, Const(_, _)) => false
-      case (Var(x, _), Var(y, _)) => x == y
-      case (Var(_, tp1), Typ(tp2, _)) => isSubType(tp1, tp2) || tryDecompose2(tp2)
-      case (Var(_, _), Or(ss)) => ss.exists(isSubspace(a, _))
-      case (Var(_, _), _) => false
-      case (_, Var(_, _)) => false
     }
+
+    debug.println(s"${show(a)} < ${show(b)} = $res")
+
+    res
   }
 
   /** Intersection of two spaces  */
@@ -175,7 +162,7 @@ trait SpaceLogic {
     def tryDecompose1(tp: Type) = intersect(Or(decompose(tp)), b)
     def tryDecompose2(tp: Type) = intersect(a, Or(decompose(tp)))
 
-    (a, b) match {
+    val res = (a, b) match {
       case (Empty, _) | (_, Empty) => Empty
       case (_, Or(ss)) => Or(ss.map(intersect(a, _)).filterConserve(_ ne Empty))
       case (Or(ss), _) => Or(ss.map(intersect(_, b)).filterConserve(_ ne Empty))
@@ -199,31 +186,11 @@ trait SpaceLogic {
         if (!isEqualType(tp1, tp2)) Empty
         else if (ss1.zip(ss2).exists(p => simplify(intersect(p._1, p._2)) == Empty)) Empty
         else Kon(tp1, ss1.zip(ss2).map((intersect _).tupled))
-      case (Const(v1, _), Const(v2, _)) =>
-        if (v1 == v2) a else Empty
-      case (Const(_, tp1), Typ(tp2, _)) =>
-        if (isSubType(tp1, tp2)) a
-        else if (canDecompose(tp2)) tryDecompose2(tp2)
-        else Empty
-      case (Const(_, _), _) => Empty
-      case (Typ(tp1, _), Const(_, tp2)) =>
-        if (isSubType(tp2, tp1)) b
-        else if (canDecompose(tp1)) tryDecompose1(tp1)
-        else Empty
-      case (_, Const(_, _)) => Empty
-      case (Var(x, _), Var(y, _)) =>
-        if (x == y) a else Empty
-      case (Var(_, tp1), Typ(tp2, _)) =>
-        if (isSubType(tp1, tp2)) a
-        else if (canDecompose(tp2)) tryDecompose2(tp2)
-        else Empty
-      case (Var(_, _), _) => Empty
-      case (Typ(tp1, _), Var(_, tp2)) =>
-        if (isSubType(tp2, tp1)) b
-        else if (canDecompose(tp1)) tryDecompose1(tp1)
-        else Empty
-      case (_, Var(_, _)) => Empty
     }
+
+    debug.println(s"${show(a)} & ${show(b)} = ${show(res)}")
+
+    res
   }
 
   /** The space of a not covered by b */
@@ -231,7 +198,7 @@ trait SpaceLogic {
     def tryDecompose1(tp: Type) = minus(Or(decompose(tp)), b)
     def tryDecompose2(tp: Type) = minus(a, Or(decompose(tp)))
 
-    (a, b) match {
+    val res = (a, b) match {
       case (Empty, _) => Empty
       case (_, Empty) => a
       case (Typ(tp1, _), Typ(tp2, _)) =>
@@ -264,26 +231,11 @@ trait SpaceLogic {
           Or(ss1.zip(ss2).map((minus _).tupled).zip(0 to ss2.length - 1).map {
               case (ri, i) => Kon(tp1, ss1.updated(i, ri))
             })
-      case (Const(v1, _), Const(v2, _)) =>
-        if (v1 == v2) Empty else a
-      case (Const(_, tp1), Typ(tp2, _)) =>
-        if (isSubType(tp1, tp2)) Empty
-        else if (canDecompose(tp2)) tryDecompose2(tp2)
-        else a
-      case (Const(_, _), _) => a
-      case (Typ(tp1, _), Const(_, tp2)) =>  // Boolean & Java enum
-        if (canDecompose(tp1)) tryDecompose1(tp1)
-        else a
-      case (_, Const(_, _)) => a
-      case (Var(x, _), Var(y, _)) =>
-        if (x == y) Empty else a
-      case (Var(_, tp1), Typ(tp2, _)) =>
-        if (isSubType(tp1, tp2)) Empty
-        else if (canDecompose(tp2)) tryDecompose2(tp2)
-        else a
-      case (Var(_, _), _) => a
-      case (_, Var(_, _)) => a
     }
+
+    debug.println(s"${show(a)} - ${show(b)} = ${show(res)}")
+
+    res
   }
 }
 
@@ -297,19 +249,14 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
    *  otherwise approximate extractors to Empty
    */
   def project(pat: Tree, roundUp: Boolean = true)(implicit ctx: Context): Space = pat match {
-    case Literal(c) => Const(c, c.tpe)
-    case _: BackquotedIdent => Var(pat.symbol, pat.tpe)
+    case Literal(c) =>
+      if (c.value.isInstanceOf[Symbol])
+        Typ(c.value.asInstanceOf[Symbol].termRef, false)
+      else
+        Typ(ConstantType(c), false)
+    case _: BackquotedIdent => Typ(pat.tpe, false)
     case Ident(_) | Select(_, _) =>
-      pat.tpe.stripAnnots match {
-        case tp: TermRef =>
-          if (pat.symbol.is(Enum))
-            Const(Constant(pat.symbol), tp)
-          else if (tp.underlyingIterator.exists(_.classSymbol.is(Module)))
-            Typ(tp.widenTermRefExpr.stripAnnots, false)
-          else
-            Var(pat.symbol, tp)
-        case tp => Typ(tp, false)
-      }
+      Typ(pat.tpe.stripAnnots, false)
     case Alternative(trees) => Or(trees.map(project(_, roundUp)))
     case Bind(_, pat) => project(pat)
     case UnApply(_, _, pats) =>
@@ -345,7 +292,9 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
   /** Is `tp1` a subtype of `tp2`?  */
   def isSubType(tp1: Type, tp2: Type): Boolean = {
     // check SI-9657 and tests/patmat/gadt.scala
-    erase(tp1) <:< erase(tp2)
+    val res = erase(tp1) <:< erase(tp2)
+    debug.println(s"${tp1.show} <:< ${tp2.show} = $res")
+    res
   }
 
   def isEqualType(tp1: Type, tp2: Type): Boolean = tp1 =:= tp2
@@ -373,19 +322,23 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
       }
     }
 
+    debug.println(s"candidates for ${tp.show} : [${children.map(_.show).mkString(", ")}]")
+
     tp match {
       case OrType(tp1, tp2) => List(Typ(tp1, true), Typ(tp2, true))
       case _ if tp =:= ctx.definitions.BooleanType =>
         List(
-          Const(Constant(true), ctx.definitions.BooleanType),
-          Const(Constant(false), ctx.definitions.BooleanType)
+          Typ(ConstantType(Constant(true)), true),
+          Typ(ConstantType(Constant(false)), true)
         )
       case _ if tp.classSymbol.is(Enum) =>
-        children.map(sym => Const(Constant(sym), tp))
+        children.map(sym => Typ(sym.termRef, true))
       case _ =>
         val parts = children.map { sym =>
           if (sym.is(ModuleClass))
-            sym.asClass.classInfo.selfType
+            refine(tp, sym.sourceModule.termRef)
+          else if (sym.isTerm)
+            refine(tp, sym.termRef)
           else if (sym.info.typeParams.length > 0 || tp.isInstanceOf[TypeRef])
             refine(tp, sym.typeRef)
           else
@@ -393,9 +346,13 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
         } filter { tpe =>
           // Child class may not always be subtype of parent:
           // GADT & path-dependent types
-          tpe <:< expose(tp)
+          val res = tpe <:< expose(tp)
+          if (!res) debug.println(s"unqualified child ousted: ${tpe.show} !< ${tp.show}")
+          res
         }
 
+        debug.println(s"${tp.show} decomposes to [${parts.map(_.show).mkString(", ")}]")
+
         parts.map(Typ(_, true))
     }
   }
@@ -409,20 +366,26 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
    *  `path2`, then return `path1.B`.
    */
   def refine(tp1: Type, tp2: Type): Type = (tp1, tp2) match {
-    case (tp1: RefinedType, _) => tp1.wrapIfMember(refine(tp1.parent, tp2))
+    case (tp1: RefinedType, _: TypeRef) => tp1.wrapIfMember(refine(tp1.parent, tp2))
     case (tp1: HKApply, _) => refine(tp1.superType, tp2)
-    case (TypeRef(ref1: TypeProxy, _), tp2 @ TypeRef(ref2: TypeProxy, name)) =>
-      if (ref1.underlying <:< ref2.underlying) TypeRef(ref1, name) else tp2
+    case (TypeRef(ref1: TypeProxy, _), tp2 @ TypeRef(ref2: TypeProxy, _)) =>
+      if (ref1.underlying <:< ref2.underlying) tp2.derivedSelect(ref1) else tp2
+    case (TypeRef(ref1: TypeProxy, _), tp2 @ TermRef(ref2: TypeProxy, _)) =>
+      if (ref1.underlying <:< ref2.underlying) tp2.derivedSelect(ref1) else tp2
     case _ => tp2
   }
 
   /** Abstract sealed types, or-types, Boolean and Java enums can be decomposed */
   def canDecompose(tp: Type): Boolean = {
-    tp.classSymbol.is(allOf(Abstract, Sealed)) ||
+    val res = tp.classSymbol.is(allOf(Abstract, Sealed)) ||
       tp.classSymbol.is(allOf(Trait, Sealed)) ||
       tp.isInstanceOf[OrType] ||
       tp =:= ctx.definitions.BooleanType ||
-      tp.classSymbol.is(Enum)
+      tp.classSymbol.is(allOf(Enum, Sealed))  // Enum value doesn't have Sealed flag
+
+    debug.println(s"decomposable: ${tp.show} = $res")
+
+    res
   }
 
   /** Show friendly type name with current scope in mind
@@ -474,14 +437,12 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
   def show(s: Space): String = {
     def doShow(s: Space, mergeList: Boolean = false): String = s match {
       case Empty => ""
-      case Const(v, _) => v.show
-      case Var(x, _) => x.show
+      case Typ(c: ConstantType, _) => c.value.show
+      case Typ(tp: TermRef, _) => tp.symbol.showName
       case Typ(tp, decomposed) =>
         val sym = tp.widen.classSymbol
 
-        if (sym.is(ModuleClass))
-          showType(tp)
-        else if (ctx.definitions.isTupleType(tp))
+        if (ctx.definitions.isTupleType(tp))
           signature(tp).map(_ => "_").mkString("(", ", ", ")")
         else if (sym.showFullName == "scala.collection.immutable.::")
           if (mergeList) "_" else "List(_)"
@@ -523,7 +484,9 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
     }
 
     val Match(sel, cases) = tree
-    isCheckable(sel.tpe.widen.deAnonymize.dealiasKeepAnnots)
+    val res = isCheckable(sel.tpe.widen.deAnonymize.dealiasKeepAnnots)
+    debug.println(s"checkable: ${sel.show} = $res")
+    res
   }
 
 
@@ -584,7 +547,11 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
     val selTyp = sel.tpe.widen.deAnonymize.dealias
 
 
-    val patternSpace = cases.map(x => project(x.pat)).reduce((a, b) => Or(List(a, b)))
+    val patternSpace = cases.map({ x =>
+      val space = project(x.pat)
+      debug.println(s"${x.pat.show} projects to ${show(space)}")
+      space
+    }).reduce((a, b) => Or(List(a, b)))
     val uncovered = simplify(minus(Typ(selTyp, true), patternSpace))
 
     if (uncovered != Empty)