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liufengyunliufengyun
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Merge pull request #3510 from dotty-staging/simple-gadt-check
A simple way to check exhaustivity of GADTs
2 parents 60d04ca + cd5a1d1 commit 7e919b6

14 files changed

+158
-7
lines changed

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

Lines changed: 50 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -708,6 +708,38 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
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else text
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}
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/** Whether the counterexample is satisfiable. The space is flattened and non-empty. */
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def satisfiable(sp: Space): Boolean = {
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def impossible: Nothing = throw new AssertionError("`satisfiable` only accepts flattened space.")
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def genConstraint(space: Space): List[(Type, Type)] = space match {
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case Prod(tp, unappTp, unappSym, ss, _) =>
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val tps = signature(unappTp, unappSym, ss.length)
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ss.zip(tps).flatMap {
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case (sp : Prod, tp) => sp.tp -> tp :: genConstraint(sp)
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case (Typ(tp1, _), tp2) => tp1 -> tp2 :: Nil
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case _ => impossible
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}
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case Typ(_, _) => Nil
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case _ => impossible
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}
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def checkConstraint(constrs: List[(Type, Type)])(implicit ctx: Context): Boolean = {
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val tvarMap = collection.mutable.Map.empty[Symbol, TypeVar]
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val typeParamMap = new TypeMap() {
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override def apply(tp: Type): Type = tp match {
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case tref: TypeRef if tref.symbol.is(TypeParam) =>
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tvarMap.getOrElseUpdate(tref.symbol, newTypeVar(tref.underlying.bounds))
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case tp => mapOver(tp)
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}
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}
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constrs.forall { case (tp1, tp2) => typeParamMap(tp1) <:< typeParamMap(tp2) }
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}
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checkConstraint(genConstraint(sp))(ctx.fresh.setNewTyperState())
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}
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/** Display spaces */
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def show(s: Space): String = {
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def params(tp: Type): List[Type] = tp.classSymbol.primaryConstructor.info.firstParamTypes
@@ -775,6 +807,16 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
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res
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}
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/** Whehter counter-examples should be further checked? True for GADTs. */
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def shouldCheckExamples(tp: Type): Boolean = {
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new TypeAccumulator[Boolean] {
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override def apply(b: Boolean, tp: Type): Boolean = tp match {
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case tref: TypeRef if tref.symbol.is(TypeParam) && variance != 1 => true
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case tp => b || foldOver(b, tp)
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}
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}.apply(false, tp)
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}
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def checkExhaustivity(_match: Match): Unit = {
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val Match(sel, cases) = _match
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val selTyp = sel.tpe.widen.dealias
@@ -785,10 +827,15 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
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debug.println(s"${x.pat.show} ====> ${show(space)}")
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space
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}).reduce((a, b) => Or(List(a, b)))
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val uncovered = simplify(minus(Typ(selTyp, true), patternSpace), aggressive = true)
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if (uncovered != Empty)
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ctx.warning(PatternMatchExhaustivity(show(uncovered)), sel.pos)
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val checkGADTSAT = shouldCheckExamples(selTyp)
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val uncovered =
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flatten(simplify(minus(Typ(selTyp, true), patternSpace), aggressive = true))
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.filter(s => s != Empty && (!checkGADTSAT || satisfiable(s)))
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if (uncovered.nonEmpty)
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ctx.warning(PatternMatchExhaustivity(show(Or(uncovered))), sel.pos)
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}
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def checkRedundancy(_match: Match): Unit = {

‎tests/patmat/3454.scala‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,10 @@
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object O {
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sealed trait Expr[T]
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case class BExpr(bool: Boolean) extends Expr[Boolean]
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case class IExpr(int: Int) extends Expr[Int]
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def join[T](e1: Expr[T], e2: Expr[T]): Expr[T] = (e1, e2) match {
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case (IExpr(i1), IExpr(i2)) => IExpr(i1 + i2)
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case (BExpr(b1), BExpr(b2)) => BExpr(b1 & b2)
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}
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}

‎tests/patmat/exhausting.check‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3,4 +3,4 @@
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32: Pattern Match Exhaustivity: List(_, _: _*)
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39: Pattern Match Exhaustivity: Bar3
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44: Pattern Match Exhaustivity: (Bar2, Bar2)
6-
53: Pattern Match Exhaustivity: (Bar2, Bar2), (Bar2, Bar1), (Bar1, Bar3), (Bar1, Bar2)
6+
50: Pattern Match Exhaustivity: (Bar2, Bar2)

‎tests/patmat/exhausting.scala‎

Lines changed: 0 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -46,9 +46,6 @@ object Test {
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case (Bar2, Bar3) => ()
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case (Bar3, _) => ()
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}
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// fails for: (Bar1, Bar2)
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// fails for: (Bar1, Bar3)
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// fails for: (Bar2, Bar1)
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// fails for: (Bar2, Bar2)
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def fail5[T](xx: (Foo[T], Foo[T])) = xx match {
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case (Bar1, Bar1) => ()

‎tests/patmat/gadt-basic.scala‎

Lines changed: 23 additions & 0 deletions
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@@ -0,0 +1,23 @@
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object O1 {
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sealed trait Expr[T]
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case class BExpr(bool: Boolean) extends Expr[Boolean]
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case class IExpr(int: Int) extends Expr[Int]
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def join[T](e1: Expr[T], e2: Expr[T]): Expr[T] = (e1, e2) match {
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case (IExpr(i1), IExpr(i2)) => IExpr(i1 + i2)
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case (BExpr(b1), BExpr(b2)) => BExpr(b1 & b2)
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}
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}
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object O2 {
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sealed trait GADT[A, B]
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case object IntString extends GADT[Int, String]
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case object IntFloat extends GADT[Int, Float]
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case object FloatFloat extends GADT[Float, Float]
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def m[A, B](g1: GADT[A, B], g2: GADT[A, B]) = (g1, g2) match {
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case (IntString, IntString) => ;
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case (IntFloat, IntFloat) => ;
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case (FloatFloat, FloatFloat) => ;
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}
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}

‎tests/patmat/gadt-covariant.check‎

Lines changed: 1 addition & 0 deletions
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@@ -0,0 +1 @@
1+
6: Pattern Match Exhaustivity: (BExpr(_), IExpr(_)), (IExpr(_), BExpr(_))

‎tests/patmat/gadt-covariant.scala‎

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@@ -0,0 +1,10 @@
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object O {
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sealed trait Expr[+T]
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case class IExpr(x: Int) extends Expr[Int]
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case class BExpr(b: Boolean) extends Expr[Boolean]
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def foo[T](x: Expr[T], y: Expr[T]) = (x, y) match {
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case (IExpr(_), IExpr(_)) => true
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case (BExpr(_), BExpr(_)) => false
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}
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}

‎tests/patmat/gadt-invariant.scala‎

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@@ -0,0 +1,10 @@
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object O {
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sealed trait Expr[T]
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case class IExpr(x: Int) extends Expr[Int]
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case class BExpr(b: Boolean) extends Expr[Boolean]
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def foo[T](x: Expr[T], y: Expr[T]) = (x, y) match {
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case (IExpr(_), IExpr(_)) => true
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case (BExpr(_), BExpr(_)) => false
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}
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}

‎tests/patmat/gadt-nontrivial.check‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
7: Pattern Match Exhaustivity: (IntExpr(_), AddExpr(_, _))

‎tests/patmat/gadt-nontrivial.scala‎

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,12 @@
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object O {
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sealed trait Expr[T]
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case class BoolExpr(v: Boolean) extends Expr[Boolean]
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case class IntExpr(v: Int) extends Expr[Int]
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case class AddExpr(e1: Expr[Int], e2: Expr[Int]) extends Expr[Int]
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def join[T](e1: Expr[T], e2: Expr[T]): Expr[T] = (e1, e2) match {
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case (BoolExpr(b1), BoolExpr(b2)) => BoolExpr(b1 && b2)
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case (IntExpr(i1), IntExpr(i2)) => IntExpr(i1 + i2)
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case (AddExpr(ei1, ei2), ie) => join(join(ei1, ei2), ie)
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}
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}

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