fix #23261 Handle ConstantType comparison for floating-point 0.0 with sign sensitivity

- Ensure match types distinguish between 0.0 and -0.0 in pattern matching.
- This enables accurate reduction in match types involving Double constants.

Author: kijuky

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -401,7 +401,13 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         compareErasedValueType
       case ConstantType(v2) =>
         tp1 match {
-          case ConstantType(v1) => v1.value == v2.value && recur(v1.tpe, v2.tpe)
+          case ConstantType(v1) =>
+            (v1.value, v2.value) match {
+              // To distinguish 0.0 and -0.0, floating-point numbers use the equals method of their boxing type.
+              case (d1: Double, d2: Double) => java.lang.Double.valueOf(d1).equals(java.lang.Double.valueOf(d2)) && recur(v1.tpe, v2.tpe)
+              case (f1: Float, f2: Float) => java.lang.Float.valueOf(f1).equals(java.lang.Float.valueOf(f2)) && recur(v1.tpe, v2.tpe)
+              case _ => v1.value == v2.value && recur(v1.tpe, v2.tpe)
+            }
           case _ => secondTry
         }
       case tp2: AnyConstantType =>

tests/neg/i23261.scala

@@ -0,0 +1,7 @@
+@main def main(): Unit =
+  summon[0.0 =:= -0.0]
+  val d: 0.0 = -0.0
+  val d2: -0.0 = 0.0
+  summon[0.0f =:= -0.0f]
+  val f: 0.0f = -0.0f
+  val f2: -0.0f = 0.0f

tests/pos/i23261.scala

@@ -0,0 +1,46 @@
+type DoubleToString[D <: Double] <: String = D match
+  case 0.0 => "0.0"
+  case -0.0 => "-0.0"
+  case _ => "_"
+
+type DoubleToString2[D <: Double] <: String = D match
+  case 0.0 => "0.0"
+  case _ => "_"
+
+type DoubleToString3[D <: Double] <: String = D match
+  case -0.0 => "-0.0"
+  case _ => "_"
+
+type FloatToString[F <: Float] <: String = F match
+  case 0.0f => "0.0f"
+  case -0.0f => "-0.0f"
+  case _ => "_"
+
+type FloatToString2[F <: Float] <: String = F match
+  case 0.0f => "0.0f"
+  case _ => "_"
+
+type FloatToString3[F <: Float] <: String = F match
+  case -0.0f => "-0.0f"
+  case _ => "_"
+
+@main def main(): Unit = {
+  summon[0.0 =:= 0.0]
+  summon[-0.0 =:= -0.0]
+  summon[DoubleToString[0.0] =:= "0.0"]
+  summon[DoubleToString[-0.0] =:= "-0.0"]
+  summon[DoubleToString[3.14] =:= "_"]
+  summon[DoubleToString2[0.0] =:= "0.0"]
+  summon[DoubleToString2[-0.0] =:= "_"]
+  summon[DoubleToString3[-0.0] =:= "-0.0"]
+  summon[DoubleToString3[0.0] =:= "_"]
+  summon[0.0f =:= 0.0f]
+  summon[-0.0f =:= -0.0f]
+  summon[FloatToString[0.0f] =:= "0.0f"]
+  summon[FloatToString[-0.0f] =:= "-0.0f"]
+  summon[FloatToString[3.14f] =:= "_"]
+  summon[FloatToString2[0.0f] =:= "0.0f"]
+  summon[FloatToString2[-0.0f] =:= "_"]
+  summon[FloatToString3[-0.0f] =:= "-0.0f"]
+  summon[FloatToString3[0.0f] =:= "_"]
+}