hijack reflect.ClassManifest definition

Author: bishabosha

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

@@ -4,8 +4,8 @@ package core
 
 import scala.annotation.{threadUnsafe => tu}
 import Types._, Contexts._, Symbols._, SymDenotations._, StdNames._, Names._, Phases._
-import Flags._, Scopes._, Decorators._, NameOps._, Periods._, NullOpsDecorator._
-import unpickleScala2.Scala2Unpickler.ensureConstructor
+import Flags._, Scopes._, Decorators._, NameOps._, Periods._, NullOpsDecorator._, Annotations.Annotation
+import unpickleScala2.Scala2Unpickler, Scala2Unpickler.ensureConstructor
 import scala.collection.mutable
 import collection.mutable
 import Denotations.SingleDenotation
@@ -778,6 +778,22 @@ class Definitions {
     else
       NoSymbol
   }
+  @tu lazy val ClassManifestAlias: Symbol = {
+    // `scala.reflect.ClassManifest` is a type alias to `scala.reflect.ClassTag`,
+    // however we need to prevent it from being dealiased for the purpose of summoning of
+    // a `ClassManifest`, which has a different result in Scala 2.
+    // With this solution values of `ClassManifest` and `ClassTag` are still interchangeable.
+    val alias = ReflectPackageClass.requiredType("ClassManifest")
+    alias.infoOrCompleter match
+      case original: LazyType =>
+        alias.info = new LazyType:
+          def complete(denot: SymDenotation)(using Context): Unit =
+            original.complete(denot) // complete it as normal, we then extract the type in the next step
+            val TypeAlias(HKTypeLambda(params, ref)) = (alias.info: @unchecked)
+            val annot = Annotation(UncheckedAnnot) // could be any annotation really
+            alias.info = HKTypeLambda.fromParams(params, TypeBounds(ref, AnnotatedType(ref, annot)))
+    alias
+  }
   @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")
@@ -1796,7 +1812,7 @@ class Definitions {
     this.initCtx = ctx
     if (!isInitialized) {
       // force initialization of every symbol that is synthesized or hijacked by the compiler
-      val forced = syntheticCoreClasses ++ syntheticCoreMethods ++ ScalaValueClasses() :+ JavaEnumClass
+      val forced = syntheticCoreClasses ++ syntheticCoreMethods ++ ScalaValueClasses() :+ JavaEnumClass :+ ClassManifestAlias
 
       isInitialized = true
     }

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -731,6 +731,11 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
       case tp: AndOrType =>
         // scalajs.js.|.UnionOps has a type parameter upper-bounded by `_ | _`
         tp.derivedAndOrType(mapArg(tp.tp1).bounds.hi, mapArg(tp.tp2).bounds.hi)
+      case tp @ AnnotatedType(inner, annot) =>
+        // added to support hijacking of `scala.reflect.ClassManifest`,
+        // we set its info to `[T] >: ClassTag[T] <: ClassTag[T] @unchecked`
+        val inner1 = elim(inner)
+        tp.derivedAnnotatedType(inner1, annot)
       case _ =>
         tp
     }

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

@@ -26,7 +26,8 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
 
   /** Handlers to synthesize implicits for special types */
   type SpecialHandler = (Type, Span) => Context ?=> Tree
-  private type SpecialHandlers = List[(ClassSymbol, SpecialHandler)]
+  type SpecialHandlerGen = Type => Context ?=> SpecialHandler
+  private type SpecialHandlers = List[(ClassSymbol, SpecialHandlerGen)]
 
   val synthesizedClassTag: SpecialHandler = (formal, span) =>
     formal.argInfos match
@@ -442,15 +443,9 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
           .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 findManifest(tp: Type, manifestClass: Symbol = if full then defn.ManifestClass else defn.ClassManifestAlias) =
+        materializeImplicit(manifestClass.typeRef.appliedTo(tp), span)
 
       def findSubManifest(tp: Type) =
         findManifest(tp, if (full) defn.ManifestClass else defn.OptManifestClass)
@@ -564,17 +559,24 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
 
   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.ManifestClass        -> synthesizedManifest,
-    defn.OptManifestClass     -> synthesizedOptManifest,
+  val synthesizedClassManifest: SpecialHandler = manifestOfFactory(defn.ClassManifestAlias)
+
+  def genSynthesizedClassTag(formal: Type)(using Context): SpecialHandler =
+    if formal.dealias.typeSymbol == defn.ClassManifestAlias then
+      synthesizedClassManifest
+    else
+      synthesizedClassTag
+
+  val specialHandlers: SpecialHandlers = List(
+    defn.ClassTagClass        -> genSynthesizedClassTag,
+    defn.TypeTestClass        -> Function.const(synthesizedTypeTest),
+    defn.CanEqualClass        -> Function.const(synthesizedCanEqual),
+    defn.ValueOfClass         -> Function.const(synthesizedValueOf),
+    defn.Mirror_ProductClass  -> Function.const(synthesizedProductMirror),
+    defn.Mirror_SumClass      -> Function.const(synthesizedSumMirror),
+    defn.MirrorClass          -> Function.const(synthesizedMirror),
+    defn.ManifestClass        -> Function.const(synthesizedManifest),
+    defn.OptManifestClass     -> Function.const(synthesizedOptManifest),
   )
 
   def tryAll(formal: Type, span: Span)(using Context): Tree =
@@ -587,10 +589,10 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
             tp.baseType(cls)
         val base = baseWithRefinements(formal)
         val result =
-          if (base <:< formal.widenExpr)
-            // With the subtype test we enforce that the searched type `formal` is of the right form
-            handler(base, span)
-          else EmptyTree
+          if base <:< formal.widenExpr then
+            handler(formal)(base, span)
+          else
+            EmptyTree
         result.orElse(recur(rest))
       case Nil =>
         EmptyTree

tests/disabled/reflect/neg/interop_abstypetags_arenot_classmanifests.check

@@ -0,0 +1,6 @@
+
+
+-- Error: tests/neg/interop_abstypetags_arenot_classmanifests/Test_3.scala:6:40 ----------------------------------------
+6 |    println(implicitly[ClassManifest[T]]) // error
+  |                                        ^
+  |                                        No ClassManifest available for T.

tests/disabled/reflect/neg/interop_abstypetags_arenot_classmanifests.scala

@@ -0,0 +1,12 @@
+import scala.reflect.runtime.universe._
+import scala.reflect.ClassManifest
+
+object Test extends App {
+  def weakTypeTagIsnotClassManifest[T: WeakTypeTag] = {
+    println(implicitly[ClassManifest[T]]) // error
+  }
+
+  // weakTypeTagIsnotClassManifest[Int]
+  // weakTypeTagIsnotClassManifest[String]
+  // weakTypeTagIsnotClassManifest[Array[Int]]
+}

tests/disabled/reflect/neg/interop_typetags_arenot_classmanifests.check

@@ -0,0 +1,8 @@
+package scala.reflect.api
+
+trait TypeTags { self: Universe =>
+  trait WeakTypeTag[T]
+  trait TypeTag[T] extends WeakTypeTag[T]
+}
+
+abstract class Universe extends TypeTags

tests/disabled/reflect/neg/interop_typetags_arenot_classmanifests.scala

@@ -0,0 +1,7 @@
+package scala.reflect
+
+package object runtime {
+
+  lazy val universe: api.Universe = new api.Universe {}
+
+}

tests/neg/interop_abstypetags_arenot_classmanifests.check

@@ -0,0 +1,6 @@
+
+
+-- Error: tests/neg/interop_typetags_arenot_classmanifests/Test_3.scala:6:40 -------------------------------------------
+6 |    println(implicitly[ClassManifest[T]]) // error
+  |                                        ^
+  |                                        No ClassManifest available for T.

tests/neg/interop_abstypetags_arenot_classmanifests/Test_3.scala

@@ -0,0 +1,12 @@
+import scala.reflect.runtime.universe._
+import scala.reflect.ClassManifest
+
+object Test extends App {
+  def typeTagIsnotClassManifest[T: TypeTag] = {
+    println(implicitly[ClassManifest[T]]) // error
+  }
+
+  // typeTagIsnotClassManifest[Int]
+  // typeTagIsnotClassManifest[String]
+  // typeTagIsnotClassManifest[Array[Int]]
+}

tests/neg/interop_abstypetags_arenot_classmanifests/api_1.scala

@@ -0,0 +1,8 @@
+package scala.reflect.api
+
+trait TypeTags { self: Universe =>
+  trait WeakTypeTag[T]
+  trait TypeTag[T] extends WeakTypeTag[T]
+}
+
+abstract class Universe extends TypeTags

tests/neg/interop_abstypetags_arenot_classmanifests/universe_2.scala

@@ -0,0 +1,7 @@
+package scala.reflect
+
+package object runtime {
+
+  lazy val universe: api.Universe = new api.Universe {}
+
+}

tests/neg/interop_typetags_arenot_classmanifests.check

@@ -0,0 +1,12 @@
+
+@deprecated("Suppress warnings", since="2.11")
+object Test extends App {
+  import scala.reflect.{ClassManifest, ClassTag}
+  def classTagIsClassManifest[T: ClassTag] = {
+    println(implicitly[ClassManifest[T]])
+  }
+
+  classTagIsClassManifest[Int]
+  classTagIsClassManifest[String]
+  classTagIsClassManifest[Array[Int]]
+}

tests/neg/interop_typetags_arenot_classmanifests/Test_3.scala

@@ -1,4 +1,4 @@
-import scala.reflect.{ClassTag, classTag}
+import scala.reflect.{ClassTag, classTag, ClassManifest}
 
 @deprecated("Suppress warnings", since="2.11")
 object Test extends App {

tests/neg/interop_typetags_arenot_classmanifests/api_1.scala

@@ -0,0 +1,2 @@
+scala.collection.immutable.List[scala.Option[Int]]
+Array[java.lang.String]

tests/neg/interop_typetags_arenot_classmanifests/universe_2.scala

@@ -0,0 +1,12 @@
+import scala.reflect.{ClassManifest, ClassTag}
+
+type CM[T] = reflect.ClassManifest[T] @annotation.nowarn("msg=deprecated")
+type CManifest[T] = CM[T] // test dealiasing mixed with annotated types
+
+@main def Test =
+  // manifests are ClassTags
+  val manifestListOptionInt: ClassTag[List[Option[Int]]] = summon[CManifest[List[Option[Int]]]]
+  val manifestArrayString: ClassTag[Array[String]] = summon[CManifest[Array[String]]]
+
+  println(manifestListOptionInt) // should print arguments to List
+  println(manifestArrayString)