The derivedEnumeration macro should reference fully qualified class names

core/src/main/scala-2/sttp/tapir/internal/CodecEnumerationMacro.scala

@@ -10,7 +10,7 @@ private[tapir] object CodecEnumerationMacro {
 
     // this needs to be a macro so that we can call another macro - Validator.derivedEnumeration
     c.Expr[CreateDerivedEnumerationCodec[L, T]](q"""
-      new sttp.tapir.macros.CreateDerivedEnumerationCodec(Validator.derivedEnumeration)
+      new sttp.tapir.macros.CreateDerivedEnumerationCodec(sttp.tapir.Validator.derivedEnumeration)
     """)
   }
 }

core/src/test/scala/sttp/tapir/namespacing/SchemaMacroNamespaceTest.scala

@@ -0,0 +1,19 @@
+package sttp.tapir.namespacing
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+class SchemaMacroNamespaceTest extends AnyFlatSpec with Matchers {
+
+  // #2254: the macro should reference fully qualified class names
+  it should "compile macro-generated code using derivedEnumeration in a package other than sttp.tapir" in {
+    sealed trait MyProduct
+    object MyProduct {
+      def fromString(m: String): Option[MyProduct] = ???
+    }
+    case object V1 extends MyProduct
+
+    import sttp.tapir.Codec
+    Codec.derivedEnumeration[String, MyProduct](MyProduct.fromString, _.toString)
+  }
+}