address reviews

Author: nox213

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

@@ -708,7 +708,7 @@ object SpaceEngine {
           else NoType
         }.filter(_.exists)
         parts
-      case tref: TypeRef if tref.symbol.isAbstractOrAliasType && !tref.info.hiBound.isNothingType =>
+      case tref: TypeRef if tref.isUpperBoundedAbstract =>
         rec(tref.info.hiBound, mixins)
       case _ => ListOfNoType
     end rec
@@ -727,6 +727,10 @@ object SpaceEngine {
         && cls.children.nonEmpty        // can't decompose without children
         && !sym.isOpaqueAlias           // can't instantiate subclasses to conform to an opaque type (i19275)
 
+  extension (tref: TypeRef)
+    def isUpperBoundedAbstract(using Context): Boolean =
+      tref.symbol.isAbstractOrAliasType && !tref.info.hiBound.isNothingType
+
   val ListOfNoType    = List(NoType)
   val ListOfTypNoType = ListOfNoType.map(Typ(_, decomposed = true))
 
@@ -858,10 +862,7 @@ object SpaceEngine {
       classSym.is(Case) ||
         (tpw.isInstanceOf[TypeRef] && {
           val tref = tpw.asInstanceOf[TypeRef]
-          if (tref.symbol.isAbstractOrAliasType && !tref.info.hiBound.isNothingType)
-            isCheckable(tref.info.hiBound)
-          else
-            false
+          tref.isUpperBoundedAbstract && isCheckable(tref.info.hiBound)
         })
 
     !sel.tpe.hasAnnotation(defn.UncheckedAnnot)

tests/warn/i23620b.check

@@ -7,10 +7,18 @@
    |
    | longer explanation available when compiling with `-explain`
 -- [E029] Pattern Match Exhaustivity Warning: tests/warn/i23620b.scala:23:2 --------------------------------------------
-23 |  p2 match { //warn
+23 |  p2 match { // warn
    |  ^^
    |  match may not be exhaustive.
    |
    |  It would fail on pattern case: _: Bar
    |
    | longer explanation available when compiling with `-explain`
+-- [E029] Pattern Match Exhaustivity Warning: tests/warn/i23620b.scala:37:2 --------------------------------------------
+37 |  x match // warn
+   |  ^
+   |  match may not be exhaustive.
+   |
+   |  It would fail on pattern case: B
+   |
+   | longer explanation available when compiling with `-explain`

tests/warn/i23620b.scala

@@ -20,6 +20,19 @@ object OnlyFoo:
   p match // warn
     case _: Foo => println("foo")
 
-  p2 match { //warn
+  p2 match { // warn
     case _: Foo => println("foo")
   }
+
+sealed trait S
+trait Z
+
+case object A extends S, Z
+case object B extends S, Z
+
+trait HasT:
+  type T <: S & Z
+
+def nonExhaustive(h: HasT, x: h.T) =
+  x match // warn
+    case A => ()