Fix #8671: Add regression test

tests/run-macros/i8671/Macro_1.scala

@@ -0,0 +1,28 @@
+import scala.quoted._
+
+case class FileName private(name: String)
+
+object FileName {
+  def unsafe(s: String) = new FileName(s)
+
+  implicit inline def ToFileName(inline s: String): FileName =
+    ${createFileName('{s})}
+
+  def fileNameFromString(s: String): Either[String, FileName] =
+    Right(FileName.unsafe(s))
+
+  def createFileName(fileName: Expr[String])(using qctx: QuoteContext): Expr[FileName] =
+    fileName match {
+      case e@Const(s) =>
+        fileNameFromString(s) match {
+            case Right(fn) =>
+              '{FileName.unsafe(${Expr(fn.name)})} // Or `Expr(fn)` if there is a `Liftable[FileName]`
+            case Left(_) =>
+              qctx.throwError(s"$s is not a valid file name! It must not contain a /", fileName)
+         }
+
+      case _ =>
+        qctx.throwError(s"$fileName is not a valid file name. It must be a literal string", fileName)
+    }
+}
+

tests/run-macros/i8671/Test_2.scala

@@ -0,0 +1,6 @@
+import FileName._
+
+@main def Test = {
+  val fileName1: FileName = ToFileName("fileName1")
+  println(fileName1)
+}