fix scala#9482: implement manifest algorithm

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

@@ -764,6 +764,12 @@ class Definitions {
   @tu lazy val SelectableClass: ClassSymbol = requiredClass("scala.Selectable")
   @tu lazy val WithoutPreciseParameterTypesClass: Symbol = requiredClass("scala.Selectable.WithoutPreciseParameterTypes")
 
+  @tu lazy val ManifestClass: ClassSymbol = requiredClass("scala.reflect.Manifest")
+  @tu lazy val ManifestFactoryModule: Symbol = requiredModule("scala.reflect.ManifestFactory")
+  @tu lazy val ClassManifestFactoryModule: Symbol = requiredModule("scala.reflect.ClassManifestFactory")
+  @tu lazy val OptManifestClass: ClassSymbol = requiredClass("scala.reflect.OptManifest")
+  @tu lazy val NoManifestModule: Symbol = requiredModule("scala.reflect.NoManifest")
+
   @tu lazy val ReflectPackageClass: Symbol = requiredPackage("scala.reflect.package").moduleClass
   @tu lazy val ClassTagClass: ClassSymbol = requiredClass("scala.reflect.ClassTag")
   @tu lazy val ClassTagModule: Symbol = ClassTagClass.companionModule
@@ -1200,6 +1206,8 @@ class Definitions {
 
   @tu lazy val untestableClasses: Set[Symbol] = Set(NothingClass, NullClass, SingletonClass)
 
+  @tu lazy val isPhantomClass = Set[Symbol](AnyClass, AnyValClass, NullClass, NothingClass)
+
   @tu lazy val AbstractFunctionType: Array[TypeRef] = mkArityArray("scala.runtime.AbstractFunction", MaxImplementedFunctionArity, 0)
   val AbstractFunctionClassPerRun: PerRun[Array[Symbol]] = new PerRun(AbstractFunctionType.map(_.symbol.asClass))
   def AbstractFunctionClass(n: Int)(using Context): Symbol = AbstractFunctionClassPerRun()(using ctx)(n)

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

@@ -367,7 +367,6 @@ object StdNames {
     val EnumValue: N            = "EnumValue"
     val ExistentialTypeTree: N  = "ExistentialTypeTree"
     val Flag : N                = "Flag"
-    val floatHash: N            = "floatHash"
     val Ident: N                = "Ident"
     val Import: N               = "Import"
     val Literal: N              = "Literal"
@@ -414,6 +413,7 @@ object StdNames {
     val argv : N                = "argv"
     val arrayClass: N           = "arrayClass"
     val arrayElementClass: N    = "arrayElementClass"
+    val arrayType: N            = "arrayType"
     val arrayValue: N           = "arrayValue"
     val array_apply : N         = "array_apply"
     val array_clone : N         = "array_clone"
@@ -440,6 +440,7 @@ object StdNames {
     val checkInitialized: N     = "checkInitialized"
     val ClassManifestFactory: N = "ClassManifestFactory"
     val classOf: N              = "classOf"
+    val classType: N            = "classType"
     val clone_ : N              = "clone"
     val common: N               = "common"
     val compiletime : N         = "compiletime"
@@ -481,6 +482,7 @@ object StdNames {
     val find_ : N               = "find"
     val flagsFromBits : N       = "flagsFromBits"
     val flatMap: N              = "flatMap"
+    val floatHash: N            = "floatHash"
     val foreach: N              = "foreach"
     val format: N               = "format"
     val fromDigits: N           = "fromDigits"
@@ -489,6 +491,7 @@ object StdNames {
     val genericClass: N         = "genericClass"
     val get: N                  = "get"
     val getClass_ : N           = "getClass"
+    val getClassLoader: N       = "getClassLoader"
     val getOrElse: N            = "getOrElse"
     val hasNext: N              = "hasNext"
     val hashCode_ : N           = "hashCode"
@@ -497,6 +500,7 @@ object StdNames {
     val head: N                 = "head"
     val higherKinds: N          = "higherKinds"
     val identity: N             = "identity"
+    val intersectionType: N     = "intersectionType"
     val implicitConversions: N  = "implicitConversions"
     val implicitly: N           = "implicitly"
     val in: N                   = "in"
@@ -588,6 +592,7 @@ object StdNames {
     val setSymbol: N            = "setSymbol"
     val setType: N              = "setType"
     val setTypeSignature: N     = "setTypeSignature"
+    val singleType: N           = "singleType"
     val standardInterpolator: N = "standardInterpolator"
     val staticClass : N         = "staticClass"
     val staticModule : N        = "staticModule"
@@ -626,6 +631,7 @@ object StdNames {
     val values: N               = "values"
     val view_ : N               = "view"
     val wait_ : N               = "wait"
+    val wildcardType: N         = "wildcardType"
     val withFilter: N           = "withFilter"
     val withFilterIfRefutable: N = "withFilterIfRefutable$"
     val WorksheetWrapper: N     = "WorksheetWrapper"

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

@@ -4,18 +4,21 @@ package typer
 
 import core._
 import util.Spans.Span
+import unpickleScala2.Scala2Erasure
 import Contexts._
 import Types._, Flags._, Symbols._, Types._, Names._, StdNames._, Constants._
 import TypeErasure.{erasure, hasStableErasure}
 import Decorators._
 import ProtoTypes._
 import Inferencing.{fullyDefinedType, isFullyDefined}
+import Implicits.SearchSuccess
 import ast.untpd
 import transform.SymUtils._
 import transform.TypeUtils._
 import transform.SyntheticMembers._
 import util.Property
 import annotation.{tailrec, constructorOnly}
+import collection.mutable
 
 /** Synthesize terms for special classes */
 class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
@@ -375,14 +378,166 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
           synthesizedSumMirror(formal, span)
       case _ => EmptyTree
 
+  private type Scala2RefinedType = RecType | RefinedType | AndType
+
+  /** @see dotty.tools.dotc.core.unpickleScala2.Scala2Erasure.flattenedParents */
+  private object Scala2RefinedType:
+
+    def unapply(tp: Scala2RefinedType)(using Context): Option[List[Type]] =
+
+      def checkSupported(tp: Type): Boolean = tp match
+        case AnnotatedType(_, _)     => false
+        case tp @ TypeRef(prefix, _) => !(!tp.symbol.exists && prefix.dealias.isInstanceOf[Scala2RefinedType])
+        case ground                  => true
+
+      @tailrec
+      def inner(explore: List[Type], acc: mutable.ListBuffer[Type]): Option[List[Type]] = explore match
+        case tp :: rest => tp match
+          case tp: RecType               => inner(tp.parent :: rest, acc)
+          case RefinedType(parent, _, _) => inner(parent :: rest, acc)
+          case AndType(l, r)             => inner(l :: r :: rest, acc)
+          case tp if checkSupported(tp)  => inner(rest, acc += tp)
+          case _                         => None // we can not create a manifest for unsupported parents
+
+        case nil => Some(acc.toList)
+      end inner
+
+      inner(tp :: Nil, new mutable.ListBuffer())
+
+    end unapply
+
+  end Scala2RefinedType
+
+  /** Replication of the `Implicits.ImplicitSearch.manifestOfType` algorithm found in nsc compiler.
+   *  @see (https://github.com/scala/scala/blob/0c011547b1ccf961ca427c3d3459955e618e93d5/src/compiler/scala/tools/nsc/typechecker/Implicits.scala#L1519)
+   */
+  private def manifestOfFactory(flavor: Symbol): SpecialHandler = (formal, span) =>
+
+    def materializeImplicit(formal: Type, span: Span)(using Context): Tree =
+      val arg = typer.inferImplicitArg(formal, span)
+      if arg.tpe.isError then
+        EmptyTree
+      else
+        arg
+
+    def inner(tp: Type, flavour: Symbol): Tree =
+
+      val full = flavor == defn.ManifestClass
+      val opt = flavor == defn.OptManifestClass
+
+      /* Creates a tree that calls the factory method called constructor in object scala.reflect.Manifest */
+      def manifestFactoryCall(constructor: TermName, tparg: Type, args: Tree*): Tree =
+        if args contains EmptyTree then
+          EmptyTree
+        else
+          val factory = if full then defn.ManifestFactoryModule else defn.ClassManifestFactoryModule
+          applyOverloaded(ref(factory), constructor, args.toList, tparg :: Nil, Types.WildcardType)
+            .withSpan(span)
+
+      /* Creates a tree representing one of the singleton manifests.*/
+      def findSingletonManifest(name: TermName) =
+        ref(defn.ManifestFactoryModule)
+          .select(name)
+          .ensureApplied
+          .withSpan(span)
+
+      /** Re-wraps a type in a manifest before calling `materializeImplicit` on the result
+       *
+       *  TODO: in scala 2 if not full the default is `reflect.ClassManifest`,
+       *  not `reflect.ClassTag`, which is treated differently.
+       */
+      def findManifest(tp: Type, manifestClass: Symbol = if full then defn.ManifestClass else NoSymbol) =
+        if manifestClass.exists then
+          materializeImplicit(manifestClass.typeRef.appliedTo(tp), span)
+        else
+          inner(tp, NoSymbol) // workaround so that a `ClassManifest` will be generated
+
+      def findSubManifest(tp: Type) =
+        findManifest(tp, if (full) defn.ManifestClass else defn.OptManifestClass)
+
+      def manifestOfType(tp0: Type, isLowerBound: Boolean): Tree =
+
+        val tp1 = tp0.dealiasKeepAnnots
+
+        extension [T](xs: List[T]) def isSingleton = xs.lengthCompare(1) == 0
+
+        def classManifest(clsRef: Type, args: List[Type]): Tree =
+          val classarg = ref(defn.Predef_classOf).appliedToType(tp1)
+          val suffix0 = classarg :: (args map findSubManifest)
+          val pre = clsRef.normalizedPrefix
+          val ignorePrefix = (pre eq NoPrefix) || pre.typeSymbol.isStaticOwner
+          val suffix = if ignorePrefix then suffix0 else findSubManifest(pre) :: suffix0
+          manifestFactoryCall(nme.classType, tp, suffix*)
+
+        tp1 match
+          case ThisType(_) | TermRef(_,_) => manifestFactoryCall(nme.singleType, tp, singleton(tp1))
+          case ConstantType(c)            => inner(c.tpe, defn.ManifestClass)
+
+          case tp1 @ TypeRef(pre, desig) =>
+            val tpSym = tp1.typeSymbol
+            if tpSym.isPrimitiveValueClass || defn.isPhantomClass(tpSym) then
+              if !isLowerBound && defn.isBottomClassAfterErasure(tpSym) then
+                EmptyTree // `Nothing`/`Null` manifests are ClassTags, lets not make a loophole for them
+              else
+                findSingletonManifest(tpSym.name.toTermName)
+            else if tpSym == defn.ObjectClass || tpSym == defn.AnyRefAlias then
+              findSingletonManifest(nme.Object)
+            else if tpSym.isClass then
+              classManifest(tp1, Nil)
+            else
+              EmptyTree
+
+          case tp1 @ AppliedType(tycon, args) =>
+            val tpSym = tycon.typeSymbol
+            if tpSym == defn.RepeatedParamClass then
+              EmptyTree
+            else if tpSym == defn.ArrayClass && args.isSingleton then
+              manifestFactoryCall(nme.arrayType, args.head, findManifest(args.head))
+            else if tpSym.isClass then
+              classManifest(tycon, args)
+            else
+              EmptyTree
+
+          case TypeBounds(lo, hi) if full =>
+            manifestFactoryCall(nme.wildcardType, tp,
+              manifestOfType(lo, isLowerBound = true), manifestOfType(hi, isLowerBound))
+
+          case Scala2RefinedType(parents) =>
+            if parents.isSingleton then findManifest(parents.head)
+            else if full then manifestFactoryCall(nme.intersectionType, tp, (parents map findSubManifest)*)
+            else manifestOfType(Scala2Erasure.intersectionDominator(parents), isLowerBound)
+
+          case _ =>
+            EmptyTree
+      end manifestOfType
+
+      manifestOfType(tp, isLowerBound = false) match
+        case EmptyTree if opt => ref(defn.NoManifestModule)
+        case result           => result
+
+    end inner
+
+    formal.argInfos match
+      case arg :: Nil =>
+        inner(fullyDefinedType(arg, "Manifest argument", span), flavor)
+      case _ =>
+        EmptyTree
+  end manifestOfFactory
+
+  val synthesizedManifest: SpecialHandler = manifestOfFactory(defn.ManifestClass)
+  val synthesizedOptManifest: SpecialHandler = manifestOfFactory(defn.OptManifestClass)
+
   val specialHandlers = List(
     defn.ClassTagClass        -> synthesizedClassTag,
     defn.TypeTestClass        -> synthesizedTypeTest,
     defn.CanEqualClass        -> synthesizedCanEqual,
     defn.ValueOfClass         -> synthesizedValueOf,
     defn.Mirror_ProductClass  -> synthesizedProductMirror,
     defn.Mirror_SumClass      -> synthesizedSumMirror,
-    defn.MirrorClass          -> synthesizedMirror)
+    defn.MirrorClass          -> synthesizedMirror,
+    defn.ManifestClass        -> synthesizedManifest,
+    defn.OptManifestClass     -> synthesizedOptManifest,
+  )
 
   def tryAll(formal: Type, span: Span)(using Context): Tree =
     def recur(handlers: SpecialHandlers): Tree = handlers match

tests/pos/i9482.scala

@@ -0,0 +1,11 @@
+import scala.reflect.OptManifest
+
+object Ref {
+  def make[A: OptManifest]: Ref[A] = ???
+}
+trait Ref[A]
+
+trait Foo[A] {
+  val bar = Ref.make[Int]
+  val baz: Ref[A] = Ref.make
+}