Fix #3144: more agressively check unreachability

Author: liufengyun

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

@@ -906,24 +906,25 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
   def checkRedundancy(_match: Match): Unit = {
     val Match(sel, cases) = _match
     // ignore selector type for now
-    // val selTyp = sel.tpe.widen.dealias
-
-    if (cases.length == 1) return
+    val selTyp = sel.tpe.widen.dealias
 
-    // starts from the second, the first can't be redundant
-    (1 until cases.length).foreach { i =>
+    (0 until cases.length).foreach { i =>
       // in redundancy check, take guard as false in order to soundly approximate
-      val prevs = cases.take(i).map { x =>
-        if (x.guard.isEmpty) project(x.pat)
-        else Empty
-      }.reduce((a, b) => Or(List(a, b)))
+      val prevs =
+        if (i == 0)
+          Empty
+        else
+          cases.take(i).map { x =>
+            if (x.guard.isEmpty) project(x.pat)
+            else Empty
+          }.reduce((a, b) => Or(List(a, b)))
 
       val curr = project(cases(i).pat)
 
       debug.println(s"---------------reachable? ${show(curr)}")
       debug.println(s"prev: ${show(prevs)}")
 
-      if (isSubspace(curr, prevs)) {
+      if (isSubspace(intersect(curr, Typ(selTyp, false)), prevs)) {
         ctx.warning(MatchCaseUnreachable(), cases(i).body.pos)
       }
     }

tests/patmat/3144.check

@@ -0,0 +1 @@
+7: Match case Unreachable

tests/patmat/3144c.check

@@ -0,0 +1 @@
+7: Match case Unreachable

tests/patmat/3144c.scala

@@ -0,0 +1,9 @@
+sealed trait Foo
+case class Bar(s: String)
+
+object Test {
+  def shouldError(foo: Foo): String =
+    foo match {
+      case bar: Bar => bar.s
+    }
+}

tests/patmat/andtype-opentype-interaction.check

@@ -2,5 +2,6 @@
 27: Pattern Match Exhaustivity: _: SealedClass & OpenTrait & OpenTrait2, _: AbstractClass & OpenTrait & OpenTrait2, _: Clazz & OpenTrait & OpenTrait2, _: Trait & OpenTrait & OpenTrait2
 31: Pattern Match Exhaustivity: _: Trait & OpenClass
 35: Pattern Match Exhaustivity: _: Trait & OpenTrait & OpenClass
+40: Match case Unreachable
 43: Pattern Match Exhaustivity: _: Trait & OpenAbstractClass
 47: Pattern Match Exhaustivity: _: Trait & OpenClass & OpenTrait & OpenClassSubclass

tests/patmat/andtype-refinedtype-interaction.check

@@ -1,6 +1,9 @@
 32: Pattern Match Exhaustivity: _: Trait & C1{x: Int}
+37: Match case Unreachable
+43: Match case Unreachable
 48: Pattern Match Exhaustivity: _: Clazz & (C1 | C2 | T1){x: Int} & (C3 | C4 | T2){x: Int}, _: Trait & (C1 | C2 | T1){x: Int} & (C3 | C4 | T2){x: Int}
 54: Pattern Match Exhaustivity: _: Trait & (C1 | C2 | T1){x: Int} & C3{x: Int}
+60: Match case Unreachable
 65: Pattern Match Exhaustivity: _: Trait & (C1 | C2){x: Int} & (C3 | SubC1){x: Int}
 72: Pattern Match Exhaustivity: _: Trait & (T1 & (C1 | SubC2)){x: Int} & (T2 & (C2 | C3 | SubC1)){x: Int} &
   SubSubC1{x: Int}

tests/patmat/i2253.check

@@ -1,3 +1,6 @@
-27: Pattern Match Exhaustivity: HasIntXIntM, HasIntXStringM
-28: Pattern Match Exhaustivity: HasIntXIntM
+28: Pattern Match Exhaustivity: HasIntXIntM, HasIntXStringM
 29: Pattern Match Exhaustivity: HasIntXIntM
+29: Match case Unreachable
+30: Pattern Match Exhaustivity: HasIntXIntM
+30: Match case Unreachable
+

tests/patmat/i2253.scala

@@ -22,6 +22,7 @@ object HasIntXIntM extends S {
 }
 
 trait T
+case class TA(val x: Int) extends T with S
 
 class Test {
   def onlyIntX(s: S { val x: Int }) = s match { case _: T => ; }

tests/patmat/t6450.scala

@@ -1,5 +1,5 @@
 sealed abstract class FoundNode[T]
-// case class A[T](x: T) extends FoundNode[T]
+case class A[T](x: T) extends FoundNode[T]
 
 object Foo {
   val v: (Some[_], FoundNode[_]) = (???, ???)

tests/patmat/virtpatmat_reach_sealed_unsealed.check

@@ -1,3 +1,4 @@
 16: Pattern Match Exhaustivity: false
 18: Match case Unreachable
 19: Match case Unreachable
+20: Match case Unreachable