Merge pull request #7925 from dotty-staging/fix-#7853

Fix #7853: Add regression test

Author: liufengyun

tests/pos-macros/i7853/JsonEncoder_1.scala

@@ -0,0 +1,50 @@
+import scala.deriving._
+import scala.compiletime.erasedValue
+
+trait JsonEncoder[T] {
+  def encode(elem: T): String
+}
+
+object JsonEncoder {
+  import scala.compiletime.{erasedValue, summonFrom}
+  import compiletime._
+  import scala.deriving._
+
+  inline def encodeElem[T](elem: T): String = summonFrom {
+    case encoder: JsonEncoder[T] => encoder.encode(elem)
+  }
+
+  inline def encodeElems[Elems <: Tuple](idx: Int)(value: Any): List[String] =
+    inline erasedValue[Elems] match {
+      case _: (elem *: elems1) =>
+        encodeElem[elem](productElement[elem](value, idx)) :: encodeElems[elems1](idx + 1)(value)
+      case _ => Nil
+    }
+
+  inline def derived[T](implicit ev: Mirror.Of[T]): JsonEncoder[T] = new JsonEncoder[T] {
+    def encode(value: T): String =
+      inline ev match {
+        case m: Mirror.SumOf[T] =>
+          "not supporting this case yet"
+        case m: Mirror.ProductOf[T] =>
+          val elems = encodeElems[m.MirroredElemTypes](0)(value)
+          val labels = value.asInstanceOf[Product].productElementNames
+          val keyValues = labels.zip(elems).map((k, v) => s"$k: $v")
+          "{" + (keyValues).mkString(", ") + "}"
+        case other =>
+          throw new RuntimeException("mirror was an invalid value: " + other)
+      }
+  }
+
+  given listEncoder[T]: (encoder: JsonEncoder[T]) => JsonEncoder[List[T]] {
+    def encode(list: List[T]) = s"[${ list.map(v => encoder.encode(v)).mkString(", ") }]"
+  }
+
+  given intEncoder: JsonEncoder[Int] {
+    def encode(value: Int) = value + ""
+  }
+
+  given stringEncoder: JsonEncoder[String] {
+    def encode(value: String) = value
+  }
+}

tests/pos-macros/i7853/SummonJsonEncoderTest_2.scala

@@ -0,0 +1,24 @@
+import scala.deriving._
+import scala.quoted._
+import scala.quoted.matching._
+import scala.compiletime.{erasedValue, summonFrom}
+import JsonEncoder.{given, _}
+
+object SummonJsonEncoderTest {
+
+  inline def encodeAndMessAroundType[T](value: =>T): String = ${ encodeAndMessAroundTypeImpl('value) }
+
+  def encodeAndMessAroundTypeImpl[T: Type](value: Expr[T])(given qctx: QuoteContext): Expr[String] = {
+    import qctx.tasty._
+
+    val mirrorExpr = summonExpr[Mirror.Of[T]] match {
+      case Some(mirror) => mirror
+    }
+
+    '{
+      given JsonEncoder[T] = JsonEncoder.derived($mirrorExpr)
+      val encoder = summon[JsonEncoder[T]]
+      encoder.encode($value)
+    }
+  }
+}

tests/pos-macros/i7853/Test_3.scala

@@ -0,0 +1,11 @@
+import SummonJsonEncoderTest._
+
+case class PersonSimple(name:String, age:Int)
+
+object Test {
+  val stuff = PersonSimple("Joe", 123)
+
+  def main(args: Array[String]):Unit = {
+    println(SummonJsonEncoderTest.encodeAndMessAroundType(stuff) )
+  }
+}