Merge pull request #9600 from dotty-staging/add-serializable-to-objects-in-backend

Mitigate #9596 for SJS: Make objects serializable only in the JVM back-end.

Author: smarter

compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala

@@ -238,11 +238,30 @@ trait BCodeSkelBuilder extends BCodeHelpers {
 
       val ps = claszSymbol.info.parents
       val superClass: String = if (ps.isEmpty) ObjectReference.internalName else internalName(ps.head.widenDealias.typeSymbol)
-      val interfaceNames = classBTypeFromSymbol(claszSymbol).info.interfaces map {
+      val interfaceNames0 = classBTypeFromSymbol(claszSymbol).info.interfaces map {
         case classBType =>
           if (classBType.isNestedClass) { innerClassBufferASM += classBType }
           classBType.internalName
       }
+      /* To avoid deadlocks when combining objects, lambdas and multi-threading,
+       * lambdas in objects are compiled to instance methods of the module class
+       * instead of static methods (see tests/run/deadlock.scala and
+       * https://github.com/scala/scala-dev/issues/195 for details).
+       * This has worked well for us so far but this is problematic for
+       * serialization: serializing a lambda requires serializing all the values
+       * it captures, if this lambda is in an object, this means serializing the
+       * enclosing object, which fails if the object does not extend
+       * Serializable.
+       * Because serializing objects is basically free since #5775, it seems like
+       * the simplest solution is to simply make all objects Serializable, this
+       * certainly seems preferable to deadlocks.
+       * This cannot be done earlier because Scala.js would not like it (#9596).
+       */
+      val interfaceNames =
+        if (claszSymbol.is(ModuleClass) && !interfaceNames0.contains("java/io/Serializable"))
+          interfaceNames0 :+ "java/io/Serializable"
+        else
+          interfaceNames0
 
       val flags = javaFlags(claszSymbol)
 

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -616,8 +616,6 @@ object desugar {
       parents1 = enumClassTypeRef :: Nil
     if (isCaseClass | isCaseObject)
       parents1 = parents1 :+ scalaDot(str.Product.toTypeName) :+ scalaDot(nme.Serializable.toTypeName)
-    else if (isObject)
-      parents1 = parents1 :+ scalaDot(nme.Serializable.toTypeName)
     if (isEnum)
       parents1 = parents1 :+ ref(defn.EnumClass.typeRef)
 

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

@@ -377,15 +377,18 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
     newSymbol(clazz, nme.writeReplace, Method | Private | Synthetic,
         MethodType(Nil, defn.AnyRefType), coord = clazz.coord).entered.asTerm
 
-  /** If this is a serializable static object `Foo`, add the method:
+  /** If this is a static object `Foo`, add the method:
    *
    *      private def writeReplace(): AnyRef =
    *        new scala.runtime.ModuleSerializationProxy(classOf[Foo.type])
    *
    *  unless an implementation already exists, otherwise do nothing.
+   *
+   *  All static objects receive the `Serializable` flag in the back-end, so
+   *  we do that even for objects that are not serializable at this phase.
    */
   def serializableObjectMethod(clazz: ClassSymbol)(using Context): List[Tree] =
-    if clazz.is(Module) && clazz.isStatic && clazz.isSerializable && !hasWriteReplace(clazz) then
+    if clazz.is(Module) && clazz.isStatic && !hasWriteReplace(clazz) then
       List(
         DefDef(writeReplaceDef(clazz),
           _ => New(defn.ModuleSerializationProxyClass.typeRef,

tests/run-macros/tasty-extractors-2.check

@@ -25,7 +25,7 @@ OrType(TypeRef(TermRef(ThisType(TypeRef(NoPrefix(), "<root>")), "scala"), "Int")
 Inlined(None, Nil, Block(List(ClassDef("Foo", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, Nil)), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
-Inlined(None, Nil, Block(List(ValDef("Foo", TypeIdent("Foo$"), Some(Apply(Select(New(TypeIdent("Foo$")), "<init>"), Nil))), ClassDef("Foo$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), Nil, Some(ValDef("_", Singleton(Ident("Foo")), None)), Nil)), Literal(Constant(()))))
+Inlined(None, Nil, Block(List(ValDef("Foo", TypeIdent("Foo$"), Some(Apply(Select(New(TypeIdent("Foo$")), "<init>"), Nil))), ClassDef("Foo$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, Some(ValDef("_", Singleton(Ident("Foo")), None)), Nil)), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
 Inlined(None, Nil, Block(List(TypeDef("Foo", TypeBoundsTree(Inferred(), Inferred()))), Literal(Constant(()))))
@@ -49,7 +49,7 @@ TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 Inlined(None, Nil, Block(List(ClassDef("Foo", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(DefDef("a", Nil, Nil, Inferred(), Some(Literal(Constant(0))))))), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
-Inlined(None, Nil, Block(List(ClassDef("Foo", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), TypeSelect(Select(Ident("_root_"), "scala"), "Product"), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), Nil, None, List(DefDef("copy", Nil, List(Nil), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))))), ValDef("Foo", TypeIdent("Foo$"), Some(Apply(Select(New(TypeIdent("Foo$")), "<init>"), Nil))), ClassDef("Foo$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), Applied(Inferred(), List(Inferred())), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), Nil, Some(ValDef("_", Singleton(Ident("Foo")), None)), List(DefDef("apply", Nil, List(Nil), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))), DefDef("unapply", Nil, List(List(ValDef("x$1", Inferred(), None))), Singleton(Literal(Constant(true))), Some(Literal(Constant(true))))))), Literal(Constant(()))))
+Inlined(None, Nil, Block(List(ClassDef("Foo", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), TypeSelect(Select(Ident("_root_"), "scala"), "Product"), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), Nil, None, List(DefDef("copy", Nil, List(Nil), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))))), ValDef("Foo", TypeIdent("Foo$"), Some(Apply(Select(New(TypeIdent("Foo$")), "<init>"), Nil))), ClassDef("Foo$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), Applied(Inferred(), List(Inferred()))), Nil, Some(ValDef("_", Singleton(Ident("Foo")), None)), List(DefDef("apply", Nil, List(Nil), Inferred(), Some(Apply(Select(New(Inferred()), "<init>"), Nil))), DefDef("unapply", Nil, List(List(ValDef("x$1", Inferred(), None))), Singleton(Literal(Constant(true))), Some(Literal(Constant(true))))))), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
 Inlined(None, Nil, Block(List(ClassDef("Foo1", DefDef("<init>", Nil, List(List(ValDef("a", TypeIdent("Int"), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("a", Inferred(), None)))), Literal(Constant(()))))
@@ -58,13 +58,13 @@ TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 Inlined(None, Nil, Block(List(ClassDef("Foo2", DefDef("<init>", Nil, List(List(ValDef("b", TypeIdent("Int"), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("b", Inferred(), None)))), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
-Inlined(None, Nil, Block(List(ClassDef("Foo3", DefDef("<init>", Nil, List(List(ValDef("a", TypeIdent("Int"), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("a", Inferred(), None))), ValDef("Foo3", TypeIdent("Foo3$"), Some(Apply(Select(New(TypeIdent("Foo3$")), "<init>"), Nil))), ClassDef("Foo3$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), Nil, Some(ValDef("_", Singleton(Ident("Foo3")), None)), List(DefDef("$lessinit$greater$default$1", Nil, Nil, Inferred(), Some(Literal(Constant(5))))))), Literal(Constant(()))))
+Inlined(None, Nil, Block(List(ClassDef("Foo3", DefDef("<init>", Nil, List(List(ValDef("a", TypeIdent("Int"), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("a", Inferred(), None))), ValDef("Foo3", TypeIdent("Foo3$"), Some(Apply(Select(New(TypeIdent("Foo3$")), "<init>"), Nil))), ClassDef("Foo3$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, Some(ValDef("_", Singleton(Ident("Foo3")), None)), List(DefDef("$lessinit$greater$default$1", Nil, Nil, Inferred(), Some(Literal(Constant(5))))))), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
 Inlined(None, Nil, Block(List(ClassDef("Foo4", DefDef("<init>", Nil, List(List(ValDef("a", TypeIdent("Int"), None)), List(ValDef("b", TypeIdent("Int"), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("a", Inferred(), None), ValDef("b", Inferred(), None)))), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
-Inlined(None, Nil, Block(List(ClassDef("Foo5", DefDef("<init>", Nil, List(List(ValDef("a", TypeIdent("Int"), None)), List(ValDef("b", TypeIdent("Int"), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("a", Inferred(), None), ValDef("b", Inferred(), None))), ValDef("Foo5", TypeIdent("Foo5$"), Some(Apply(Select(New(TypeIdent("Foo5$")), "<init>"), Nil))), ClassDef("Foo5$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil), TypeSelect(Select(Ident("_root_"), "scala"), "Serializable")), Nil, Some(ValDef("_", Singleton(Ident("Foo5")), None)), List(DefDef("$lessinit$greater$default$2", Nil, List(List(ValDef("a", TypeIdent("Int"), None))), Inferred(), Some(Ident("a")))))), Literal(Constant(()))))
+Inlined(None, Nil, Block(List(ClassDef("Foo5", DefDef("<init>", Nil, List(List(ValDef("a", TypeIdent("Int"), None)), List(ValDef("b", TypeIdent("Int"), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("a", Inferred(), None), ValDef("b", Inferred(), None))), ValDef("Foo5", TypeIdent("Foo5$"), Some(Apply(Select(New(TypeIdent("Foo5$")), "<init>"), Nil))), ClassDef("Foo5$", DefDef("<init>", Nil, List(Nil), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, Some(ValDef("_", Singleton(Ident("Foo5")), None)), List(DefDef("$lessinit$greater$default$2", Nil, List(List(ValDef("a", TypeIdent("Int"), None))), Inferred(), Some(Ident("a")))))), Literal(Constant(()))))
 TypeRef(ThisType(TypeRef(NoPrefix(), "scala")), "Unit")
 
 Inlined(None, Nil, Block(List(ClassDef("Foo6", DefDef("<init>", Nil, List(List(ValDef("a", TypeIdent("Int"), None)), List(ValDef("b", Singleton(Ident("a")), None))), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), Nil, None, List(ValDef("a", Inferred(), None), ValDef("b", Inferred(), None)))), Literal(Constant(()))))