Use TypeComparer.constValue in TypeEval

This uses `TypeComparer.constValue` to extract the constant in TypeEval.
This is also how constValue is implemented. So I think also using it in
TypeEval make behavior around this more consistent and predictable.

This fixes: #24717

Author: eejbyfeldt

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

@@ -2,6 +2,8 @@ package dotty.tools
 package dotc
 package core
 
+import scala.reflect.Typeable
+
 import Types.*, Contexts.*, Symbols.*, Constants.*, Decorators.*
 import config.Printers.typr
 import reporting.trace
@@ -26,33 +28,22 @@ object TypeEval:
             if tp1.isStable then tp1.fixForEvaluation else tp
           case tp => tp
 
-      def constValue(tp: Type): Option[Any] = tp.fixForEvaluation match
-        case ConstantType(Constant(n)) => Some(n)
-        case _ => None
+      extension (tp: Type) def constant[T: Typeable]: Option[T] =
+        TypeComparer.constValue(tp.fixForEvaluation).collect { case Constant(c: T) => c }
+
+      def constValue(tp: Type): Option[Any] = tp.constant[Any]
 
-      def boolValue(tp: Type): Option[Boolean] = tp.fixForEvaluation match
-        case ConstantType(Constant(n: Boolean)) => Some(n)
-        case _ => None
+      def boolValue(tp: Type): Option[Boolean] = tp.constant[Boolean]
 
-      def intValue(tp: Type): Option[Int] = tp.fixForEvaluation match
-        case ConstantType(Constant(n: Int)) => Some(n)
-        case _ => None
+      def intValue(tp: Type): Option[Int] = tp.constant[Int]
 
-      def longValue(tp: Type): Option[Long] = tp.fixForEvaluation match
-        case ConstantType(Constant(n: Long)) => Some(n)
-        case _ => None
+      def longValue(tp: Type): Option[Long] = tp.constant[Long]
 
-      def floatValue(tp: Type): Option[Float] = tp.fixForEvaluation match
-        case ConstantType(Constant(n: Float)) => Some(n)
-        case _ => None
+      def floatValue(tp: Type): Option[Float] = tp.constant[Float]
 
-      def doubleValue(tp: Type): Option[Double] = tp.fixForEvaluation match
-        case ConstantType(Constant(n: Double)) => Some(n)
-        case _ => None
+      def doubleValue(tp: Type): Option[Double] = tp.constant[Double]
 
-      def stringValue(tp: Type): Option[String] = tp.fixForEvaluation match
-        case ConstantType(Constant(n: String)) => Some(n)
-        case _ => None
+      def stringValue(tp: Type): Option[String] = tp.constant[String]
 
       // Returns Some(true) if the type is a constant.
       // Returns Some(false) if the type is not a constant.

tests/pos/i24717.scala

@@ -0,0 +1,13 @@
+import scala.compiletime.ops.int.+
+import scala.compiletime.ops.int.S
+
+object test {
+  object O {
+    opaque type O = Int
+    transparent inline def v: O = 123
+  }
+
+  val a: 123 & O.O = O.v
+  val b: S[a.type] = 124
+  val c: a.type + 1 = 124
+}