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Fix #4225: always check redundant cases except for @unchecked #4232

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Fix #4225: always check redundant cases except for @unchecked #4232

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7 changes: 2 additions & 5 deletions compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -33,11 +33,8 @@ class PatternMatcher extends MiniPhase {

// check exhaustivity and unreachability
val engine = new patmat.SpaceEngine

if (engine.checkable(tree)) {
engine.checkExhaustivity(tree)
engine.checkRedundancy(tree)
}
engine.checkExhaustivity(tree)
engine.checkRedundancy(tree)

translated.ensureConforms(tree.tpe)
}
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12 changes: 8 additions & 4 deletions compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
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Expand Up @@ -839,7 +839,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
flatten(s).map(doShow(_, false)).distinct.mkString(", ")
}

def checkable(tree: Match): Boolean = {
private def exhaustivityCheckable(sel: Tree): Boolean = {
// Possible to check everything, but be compatible with scalac by default
def isCheckable(tp: Type): Boolean =
!tp.hasAnnotation(defn.UncheckedAnnot) && {
Expand All @@ -857,9 +857,8 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
(defn.isTupleType(tpw) && tpw.argInfos.exists(isCheckable(_)))
}

val Match(sel, cases) = tree
val res = isCheckable(sel.tpe)
debug.println(s"checkable: ${sel.show} = $res")
debug.println(s"exhaustivity checkable: ${sel.show} = $res")
res
}

Expand All @@ -877,6 +876,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
val Match(sel, cases) = _match
val selTyp = sel.tpe.widen.dealias

if (!exhaustivityCheckable(sel)) return

val patternSpace = cases.map({ x =>
val space = project(x.pat)
Expand All @@ -894,11 +894,15 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
ctx.warning(PatternMatchExhaustivity(show(Or(uncovered))), sel.pos)
}

private def redundancyCheckable(sel: Tree): Boolean =
!sel.tpe.hasAnnotation(defn.UncheckedAnnot)

def checkRedundancy(_match: Match): Unit = {
val Match(sel, cases) = _match
// ignore selector type for now
val selTyp = sel.tpe.widen.dealias

if (!redundancyCheckable(sel)) return

(0 until cases.length).foreach { i =>
// in redundancy check, take guard as false in order to soundly approximate
val prevs =
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1 change: 1 addition & 0 deletions tests/patmat/i4225.check
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@@ -0,0 +1 @@
10: Match case Unreachable
12 changes: 12 additions & 0 deletions tests/patmat/i4225.scala
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@@ -0,0 +1,12 @@
object Bar {
def unapply(x: Int): Some[Int] =
Some(0)
}

object Test {
def test(x: Int) =
x match {
case Bar(a) => a
case _ => x // should be unreachable
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Can you add a test case for objects:

object Bar {
  def unapply(x: String): Some[Int] =
    Some(0)
}

object Test {
  def test(x: String) =
    x match {
      case Bar(a) => a
      case _ => x // this case is reachable, i.e. test(null)
    }
}

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@liufengyun liufengyun Apr 3, 2018 •
edited
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@allanrenucci : the exhaustivity check both in Dotty and Scalac ignores null. Otherwise, all pattern matchess without a _ will not be exhaustive. Thus in the example above, both Dotty & Scalac will report a warning.

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Sorry, I was wrong, for reachability check we can handle null thus avoid the warning:

It's implemented in https://github.com/lampepfl/dotty/compare/master...dotty-staging:fix-4225?expand=1#diff-5353f08e8d531fe0ee59335438e6cf7a.

}
}