Add initial experiments on mirror support.

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -974,6 +974,9 @@ class Definitions {
     @tu lazy val RuntimeTuples_isInstanceOfEmptyTuple: Symbol = RuntimeTuplesModule.requiredMethod("isInstanceOfEmptyTuple")
     @tu lazy val RuntimeTuples_isInstanceOfNonEmptyTuple: Symbol = RuntimeTuplesModule.requiredMethod("isInstanceOfNonEmptyTuple")
 
+  @tu lazy val JavaRecordReflectMirrorTypeRef: TypeRef = requiredClassRef("scala.runtime.JavaRecordMirror")
+  @tu lazy val JavaRecordReflectMirrorModule: Symbol = requiredModule("scala.runtime.JavaRecordMirror")
+
   @tu lazy val TupledFunctionTypeRef: TypeRef = requiredClassRef("scala.util.TupledFunction")
   def TupledFunctionClass(using Context): ClassSymbol = TupledFunctionTypeRef.symbol.asClass
   def RuntimeTupleFunctionsModule(using Context): Symbol = requiredModule("scala.runtime.TupledFunctions")

compiler/src/dotty/tools/dotc/core/SymUtils.scala

@@ -99,13 +99,14 @@ class SymUtils:
       def canAccessCtor: Boolean =
         def isAccessible(sym: Symbol): Boolean = ctx.owner.isContainedIn(sym)
         def isSub(sym: Symbol): Boolean = ctx.owner.ownersIterator.exists(_.derivesFrom(sym))
-        val ctor = self.primaryConstructor
+        val ctor = if defn.isJavaRecordClass(self) then self.javaCanonicalConstructor else self.primaryConstructor
         (!ctor.isOneOf(Private | Protected) || isSub(self)) // we cant access the ctor because we do not extend cls
         && (!ctor.privateWithin.exists || isAccessible(ctor.privateWithin)) // check scope is compatible
 
 
       def companionMirror = self.useCompanionAsProductMirror
-      if (!self.is(CaseClass)) "it is not a case class"
+
+      if (!(self.is(CaseClass) || defn.isJavaRecordClass(self))) "it is not a case class or record class"
       else if (self.is(Abstract)) "it is an abstract class"
       else if (self.primaryConstructor.info.paramInfoss.length != 1) "it takes more than one parameter list"
       else if self.isDerivedValueClass then "it is a value class"
@@ -146,7 +147,7 @@ class SymUtils:
       && (!self.is(Method) || self.is(Accessor))
 
     def useCompanionAsProductMirror(using Context): Boolean =
-      self.linkedClass.exists && !self.is(Scala2x) && !self.linkedClass.is(Case)
+      self.linkedClass.exists && !self.is(Scala2x) && !self.linkedClass.is(Case) && !defn.isJavaRecordClass(self)
 
     def useCompanionAsSumMirror(using Context): Boolean =
       def companionExtendsSum(using Context): Boolean =
@@ -249,6 +250,12 @@ class SymUtils:
     def caseAccessors(using Context): List[Symbol] =
       self.info.decls.filter(_.is(CaseAccessor))
 
+    // TODO: I'm convinced that we need to introduce a flag to get the canonical constructor.
+    //       we should also check whether the names are erased in the ctor. If not, we should
+    //       be able to infer the components directly from the constructor.
+    def javaCanonicalConstructor(using Context): Symbol =
+      self.info.decls.filter(_.isConstructor).tail.head
+
     // TODO: Check if `Synthetic` is stamped properly
     def javaRecordComponents(using Context): List[Symbol] =
       self.info.decls.filter(sym => sym.is(Synthetic) && sym.is(Method) && !sym.isConstructor)

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

@@ -345,23 +345,13 @@ object PatternMatcher {
 
         def resultTypeSym = unapp.symbol.info.resultType.typeSymbol
 
-        def isSyntheticJavaRecordUnapply(sym: Symbol) =
-          // Since the `unapply` symbol is marked as inline, the `Typer` wraps the body of the `unapply` in a separate
-          // anonymous class. The result type alone is not enough to distinguish that we're calling the synthesized unapply —
-          // we could have defined a separate `unapply` method returning a Java record somewhere, hence we resort to using
-          // the `coord`.
-          sym.is(Synthetic) && sym.isAnonymousClass && {
-            val resultSym = resultTypeSym
-            // TODO: Can a user define a separate unapply function in Java?
-            val unapplyFn = resultSym.linkedClass.info.decl(nme.unapply)
-            // TODO: This is nasty, can we add an attachment on the anonymous function for a prior link?
-            defn.isJavaRecordClass(resultSym) && unapplyFn.symbol.coord == sym.coord
-          }
-
+        // TODO: Check Scala -> Java, erased?
+        def isJavaRecordUnapply(sym: Symbol) = defn.isJavaRecordClass(resultTypeSym)
         def tupleSel(sym: Symbol) = ref(scrutinee).select(sym)
         def recordSel(sym: Symbol) = tupleSel(sym).appliedToTermArgs(Nil)
 
-        if (isSyntheticJavaRecordUnapply(unapp.symbol.owner))
+        // TODO: Move this to the correct location
+        if (isJavaRecordUnapply(unapp.symbol.owner))
           val components = resultTypeSym.javaRecordComponents.map(recordSel)
           matchArgsPlan(components, args, onSuccess)
         else if (isSyntheticScala2Unapply(unapp.symbol) && caseAccessors.length == args.length)

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

@@ -407,6 +407,12 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
     def newTupleMirror(arity: Int): Tree =
       New(defn.RuntimeTupleMirrorTypeRef, Literal(Constant(arity)) :: Nil)
 
+    def newJavaRecordReflectMirror(tpe: Type) =
+      ref(defn.JavaRecordReflectMirrorModule)
+        .select(nme.apply)
+        .appliedToType(tpe)
+        .appliedTo(clsOf(tpe))
+
     def makeProductMirror(pre: Type, cls: Symbol, tps: Option[List[Type]]): TreeWithErrors =
       val accessors = cls.caseAccessors
       val elemLabels = accessors.map(acc => ConstantType(Constant(acc.name.toString)))
@@ -427,6 +433,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
       }
       val mirrorRef =
         if cls.useCompanionAsProductMirror then companionPath(mirroredType, span)
+        else if defn.isJavaRecordClass(cls) then newJavaRecordReflectMirror(cls.typeRef)
         else if defn.isTupleClass(cls) then newTupleMirror(typeElems.size) // TODO: cls == defn.PairClass when > 22
         else anonymousMirror(monoType, MirrorImpl.OfProduct(pre), span)
       withNoErrors(mirrorRef.cast(mirrorType).withSpan(span))
@@ -458,6 +465,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
             val reason = s"it reduces to a tuple with arity $arity, expected arity <= $maxArity"
             withErrors(i"${defn.PairClass} is not a generic product because $reason")
         case MirrorSource.ClassSymbol(pre, cls) =>
+
           if cls.isGenericProduct then
             if ctx.runZincPhases then
               // The mirror should be resynthesized if the constructor of the

library/src/scala/runtime/JavaRecordMirror.scala

@@ -0,0 +1,34 @@
+package scala.runtime
+
+import java.lang.Record
+import java.lang.reflect.Constructor
+import scala.reflect.ClassTag
+
+// TODO: Rename to JavaRecordReflectMirror
+object JavaRecordMirror:
+
+  def apply[T <: Record](clazz: Class[T]): JavaRecordMirror[T] =
+    val components = clazz.getRecordComponents.nn
+    val constructorTypes = components.map(_.nn.getType.nn)
+    val constr = clazz.getDeclaredConstructor(constructorTypes*).nn
+    new JavaRecordMirror(components.length, constr)
+
+  def of[T <: Record : ClassTag]: JavaRecordMirror[T] =
+    JavaRecordMirror(summon[ClassTag[T]].runtimeClass.asInstanceOf[Class[T]])
+
+// TODO: Is a constructor serializable?
+final class JavaRecordMirror[T] private(arity: Int, constr: Constructor[T]) extends scala.deriving.Mirror.Product with Serializable:
+
+  override type MirroredMonoType <: Record
+
+  final def fromProduct(product: Product): MirroredMonoType =
+    if product.productArity != arity  then
+    throw IllegalArgumentException(s"expected Product with $arity elements, got ${product.productArity}")
+    else
+      // TODO: Check this byte code, we want to unroll to give a happy medium between JIT'ing and having tons of extra classes
+      val t = arity match
+        case 0 => constr.newInstance()
+        case 1 => constr.newInstance(product.productElement(0))
+        case 2 => constr.newInstance(product.productElement(0), product.productElement(1))
+
+      t.nn.asInstanceOf[MirroredMonoType]

tests/pos-java16+/java-records-mirror/FromScala.scala

@@ -0,0 +1,5 @@
+import scala.deriving.Mirror
+
+object C:
+  def useR2: Unit =
+    summon[Mirror.Of[R2]]

tests/pos-java16+/java-records-mirror/R2.java

@@ -0,0 +1 @@
+public record R2(int i, String s) {}