Provide mirror support after inlining

Mirror support runs in PostTyper to add new members to mirrors generated
during Typer. But some anonymous mirrors are generated during inlining.
We need to add the missing methods for them as well.

Fixes #11542
Fixes #11961
Fixes #12052

Author: odersky

compiler/src/dotty/tools/dotc/CompilationUnit.scala

@@ -43,6 +43,8 @@ class CompilationUnit protected (val source: SourceFile) {
    */
   var needsInlining: Boolean = false
 
+  var needsMirrorSupport: Boolean = false
+
   /** Will be set to `true` if contains `Quote`.
    *  The information is used in phase `Staging` in order to avoid traversing trees that need no transformations.
    */

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -50,6 +50,7 @@ class Compiler {
   protected def picklerPhases: List[List[Phase]] =
     List(new Pickler) ::            // Generate TASTY info
     List(new Inlining) ::           // Inline and execute macros
+    List(new PostInlining) ::       // Add mirror support for inlined code
     List(new Staging) ::            // Check staging levels and heal staged types
     List(new PickleQuotes) ::       // Turn quoted trees into explicit run-time data structures
     Nil

compiler/src/dotty/tools/dotc/transform/PostInlining.scala

@@ -0,0 +1,29 @@
+package dotty.tools.dotc
+package transform
+
+import core._
+import Contexts.*
+import DenotTransformers.IdentityDenotTransformer
+import Decorators.*
+import ast.tpd.*
+
+/** A phase that adds mirror support for anonymous mirrors created at inlining. */
+class PostInlining extends MacroTransform, IdentityDenotTransformer:
+  thisPhase =>
+
+  override def phaseName: String = PostInlining.name
+  override def changesMembers = true
+
+  override def run(using Context): Unit =
+    if ctx.compilationUnit.needsMirrorSupport then super.run
+
+  lazy val synthMbr: SyntheticMembers = new SyntheticMembers(thisPhase)
+
+  def newTransformer(using Context): Transformer = new Transformer:
+    override def transform(tree: Tree)(using Context): Tree =
+      super.transform(tree) match
+        case tree1: Template => synthMbr.addMirrorSupport(tree1)
+        case tree1 => tree1
+
+object PostInlining:
+  val name: String = "postInlining"

compiler/src/dotty/tools/dotc/typer/Synthesizer.scala

@@ -180,6 +180,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
    *  and mark it with given attachment so that it is made into a mirror at PostTyper.
    */
   private def anonymousMirror(monoType: Type, attachment: Property.StickyKey[Unit], span: Span)(using Context) =
+    if ctx.isAfterTyper then ctx.compilationUnit.needsMirrorSupport = true
     val monoTypeDef = untpd.TypeDef(tpnme.MirroredMonoType, untpd.TypeTree(monoType))
     val newImpl = untpd.Template(
       constr = untpd.emptyConstructor,

tests/run/i11542.scala

@@ -0,0 +1,31 @@
+object demo {
+
+  trait Reader[A]
+
+  given Reader[Int] with {}
+
+  inline def summonReader[T <: Tuple]: List[Reader[_]] = inline compiletime.erasedValue[T] match {
+    case _: EmptyTuple => Nil
+    case _: (t *: ts) => compiletime.summonInline[Reader[t]] :: summonReader[ts]
+  }
+
+  class CombinedReader[A](
+    m: deriving.Mirror.ProductOf[A],
+    childReaders: List[Reader[_]]
+  ) extends Reader[A]
+
+  inline given rdr[A <: Tuple](using m: deriving.Mirror.ProductOf[A]): Reader[A] = {
+    new CombinedReader(m, summonReader[m.MirroredElemTypes])
+  }
+
+}
+
+@main def Test() = {
+  // OK
+  //summon[demo.Reader[(Int, Int, Int)]]
+
+  // Exception in thread "main" java.lang.ClassCastException: class main$package$$anon$2 cannot be cast to class scala.deriving.Mirror$Product (main$package$$anon$2 and scala.deriving.Mirror$Product are in unnamed module of loader 'app')
+  //      at main$package$.run(main.scala:25)
+  //      at run.main(main.scala:23)
+  summon[demo.Reader[(Int, (Int, Int))]]
+}

tests/run/i11542a.scala

@@ -0,0 +1,6 @@
+type Foo = Tuple2[Int, Int]
+// case class Foo(x: Int, y: Int) // works
+class Reader(m: deriving.Mirror.ProductOf[Foo])
+given reader1(using m: deriving.Mirror.ProductOf[Foo]): Reader = new Reader(m)
+inline def summonReader(): Reader = compiletime.summonInline[Reader]
+@main def Test() = summonReader()

tests/run/i11961.check

@@ -0,0 +1,4 @@
+STRING
+BOOLEAN
+STRING
+BOOLEAN

tests/run/i11961.scala

@@ -0,0 +1,41 @@
+import scala.deriving.*
+import scala.compiletime.{erasedValue, summonInline}
+
+case class Simple(a: String, b: Boolean) derives Printable
+case class SimpleT(a: (String, Boolean)) derives Printable
+
+@main def Test: Unit = {
+
+  summon[Printable[Simple]].print // Prints STRING BOOLEAN as expected
+
+  summon[Printable[SimpleT]].print // java.lang.ClassCastException: SimpleT$$anon$1 cannot be cast to scala.deriving.Mirror$Product
+
+}
+
+trait Printable[T]:
+   def print: Unit
+
+object Printable:
+
+   given Printable[String] with
+      def print: Unit = println("STRING")
+
+   given Printable[Boolean] with
+      def print: Unit = println("BOOLEAN")
+
+   def printProduct[T](p: Mirror.ProductOf[T], elems: => List[Printable[_]]): Printable[T] =
+      new Printable[T]:
+         def print: Unit =
+            elems.foreach(_.print)
+
+   inline given derived[T](using m: Mirror.Of[T]): Printable[T] =
+      val elemInstances = summonAllPrintable[m.MirroredElemTypes]
+      inline m match
+         case p: Mirror.ProductOf[T] => printProduct(p, elemInstances)
+
+end Printable
+
+inline def summonAllPrintable[T <: Tuple]: List[Printable[_]] =
+   inline erasedValue[T] match
+      case _: EmptyTuple => Nil
+      case _: (t *: ts) => summonInline[Printable[t]] :: summonAllPrintable[ts]

tests/run/i12052/MirrorType.scala

@@ -0,0 +1,34 @@
+import scala.quoted._
+import scala.deriving._
+import scala.compiletime.{erasedValue, constValue, summonFrom, summonInline}
+
+class MyContext {
+  implicit inline def autoMirrorType[T]: MirrorType[T] = MirrorType.generic
+}
+
+trait MirrorType[T] {
+  def mirrorType: String
+}
+
+object MirrorType {
+  class Container[T]
+
+  inline def decode[T]: String =
+    summonFrom {
+      case ev: Mirror.ProductOf[T] =>
+        s"Product-${new Container[ev.MirroredElemLabels]}" // This is the part that splices in the cast
+      case m: Mirror.SumOf[T] =>
+        "Sum"
+    }
+
+  inline def generic[T]: MirrorType[T] =
+    new MirrorType[T] {
+      def mirrorType: String = decode[T]
+    }
+
+  extension[T](inline value: T)
+    inline def mirrorType = summonFrom {
+      case mt: MirrorType[T] => mt.mirrorType
+      case _ => "mirror not found"
+    }
+}

tests/run/i12052/Test.scala

@@ -0,0 +1,9 @@
+import MirrorType._
+object Test {
+  def main(args: Array[String]): Unit = {
+    val ctx = new MyContext();
+    import ctx._
+    val tup = ("foo", 1)
+    assert(tup.mirrorType.isInstanceOf[String])
+  }
+}