Cleanup implementation of Reflection.let

And fix bug in test

Author: nicolasstucki

library/src-bootstrapped/scala/tasty/reflect/TreeUtils.scala

@@ -287,15 +287,15 @@ trait TreeUtils
   def let(rhs: Term)(body: Ident => Term): Term = {
     import scala.quoted.QuoteContext
     given as QuoteContext = new QuoteContext(this)
-    type T // TODO probably it is better to use the Sealed contruct rather than let the user create their own existential type
-    implicit val rhsTpe: quoted.Type[T] = rhs.tpe.seal.asInstanceOf[quoted.Type[T]]
-    val rhsExpr = rhs.seal.cast[T]
-    val expr = '{
-      val x = $rhsExpr
-      ${
-        val id = ('x).unseal.asInstanceOf[Ident]
-        body(id).seal
-      }
+    val expr = (rhs.seal: @unchecked) match {
+      case '{ $rhsExpr: $t } =>
+        '{
+          val x = $rhsExpr
+          ${
+            val id = ('x).unseal.asInstanceOf[Ident]
+            body(id).seal
+          }
+        }
     }
     expr.unseal
   }

tests/run-macros/tasty-unsafe-let/quoted_1.scala

@@ -2,7 +2,7 @@ import scala.quoted._
 
 object Macros {
 
-  inline def let[T](rhs: T)(body: => T => Unit): Unit =
+  inline def let[T](rhs: => T)(body: => T => Unit): Unit =
     ${ impl('rhs, 'body) }
 
   private def impl[T](rhs: Expr[T], body: Expr[T => Unit]) given (qctx: QuoteContext): Expr[Unit] = {