Emit local module like lazy val

The motivation is to use the new fine-grained lock scoping that
local lazies have since #5294.

Fixes scala/scala-dev#235

Co-Authored-By: Jason Zaugg <jzaugg@gmail.com>

6 files changed, 88 insertions, 40 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Fields.scala b/src/compiler/scala/tools/nsc/transform/Fields.scala
index 6cf6a5abce..0c6982384d 100644
--- a/src/compiler/scala/tools/nsc/transform/Fields.scala
+++ b/src/compiler/scala/tools/nsc/transform/Fields.scala
@@ -193,20 +193,6 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
   // not be emitted as ACC_FINAL. They are FINAL in the Scala sense, though: cannot be overridden.
   private final val ModuleOrLazyFieldFlags = FINAL | PrivateLocal | SYNTHETIC | NEEDS_TREES
 
-  private def newModuleVarSymbol(owner: Symbol, module: Symbol, tp: Type): TermSymbol = {
-//    println(s"new module var in $site for $module of type $tp")
-    val flags = MODULEVAR | (if (owner.isClass) ModuleOrLazyFieldFlags else 0)
-
-    val moduleVar =
-      (owner.newVariable(nme.moduleVarName(module.name.toTermName), module.pos.focus, flags)
-        setInfo tp
-        addAnnotation VolatileAttr)
-
-    moduleOrLazyVarOf(module) = moduleVar
-
-    moduleVar
-  }
-
   private def moduleInit(module: Symbol, moduleVar: Symbol) = {
 //    println(s"moduleInit for $module in ${module.ownerChain} --> ${moduleVarOf.get(module)}")
     def moduleVarRef = gen.mkAttributedRef(moduleVar)
@@ -380,8 +366,16 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
           (existingGetter ne NoSymbol) && (tp matches (site memberInfo existingGetter).resultType) // !existingGetter.isDeferred && -- see (3)
         }
 
-        def newModuleVarMember(member: Symbol): TermSymbol =
-          newModuleVarSymbol(clazz, member, site.memberType(member).resultType)
+        def newModuleVarMember(module: Symbol): TermSymbol = {
+          val moduleVar =
+            (clazz.newVariable(nme.moduleVarName(module.name.toTermName), module.pos.focus, MODULEVAR | ModuleOrLazyFieldFlags)
+             setInfo site.memberType(module).resultType
+             addAnnotation VolatileAttr)
+
+          moduleOrLazyVarOf(module) = moduleVar
+
+          moduleVar
+        }
 
         def newLazyVarMember(member: Symbol): TermSymbol =
           Fields.this.newLazyVarMember(clazz, member, site.memberType(member).resultType)
@@ -531,7 +525,8 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
     def mkTypedValDef(sym: Symbol, rhs: Tree = EmptyTree) = typedPos(sym.pos)(ValDef(sym, rhs)).asInstanceOf[ValDef]
 
     /**
-      * Desugar a local `lazy val x: Int = rhs` into
+      * Desugar a local `lazy val x: Int = rhs` or a local object into
+      *
       * ```
       * val x$lzy = new scala.runtime.LazyInt()
       * def x$lzycompute(): Int =
@@ -541,10 +536,13 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
       *  }
       * def x(): Int = if (x$lzy.initialized()) x$lzy.value() else x$lzycompute()
       * ```
+      *
+      * The expansion is the same for local lazy vals and local objects,
+      * except for the name of the val ($lzy or
       */
     private def mkLazyLocalDef(lazyVal: Symbol, rhs: Tree): Tree = {
       import CODE._
-      import scala.reflect.NameTransformer.LAZY_LOCAL_SUFFIX_STRING
+      import scala.reflect.{NameTransformer => nx}
       val owner = lazyVal.owner
 
       val lazyValType = lazyVal.tpe.resultType
@@ -555,8 +553,7 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
       val lazyName  = lazyVal.name.toTermName
       val pos       = lazyVal.pos.focus
 
-      // used twice: once in the same owner as the lazy val, another time inside the compute method
-      val localLazyName = lazyName append LAZY_LOCAL_SUFFIX_STRING
+      val localLazyName = lazyName append (if (lazyVal.isModule) nx.MODULE_VAR_SUFFIX_STRING else nx.LAZY_LOCAL_SUFFIX_STRING)
 
       // The lazy holder val need not be mutable, as we write to its field.
       // In fact, it MUST not be mutable to avoid capturing it as an ObjectRef in lambdalift
@@ -730,8 +727,9 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
           val cd = super.transform(ClassDef(statSym.moduleClass, impl) setType NoType)
           if (currOwner.isClass) cd
           else { // local module -- symbols cannot be generated by info transformer, so do it all here
-            val moduleVar = newModuleVarSymbol(currOwner, statSym, statSym.info.resultType)
-            Thicket(cd :: mkTypedValDef(moduleVar) :: mkAccessor(statSym)(moduleInit(statSym, moduleVar)) :: Nil)
+            val Block(stats, _) = mkLazyLocalDef(statSym, gen.newModule(statSym, statSym.info.resultType))
+
+            Thicket(cd :: stats)
           }
 
         case tree =>
diff --git a/test/files/run/SD-235.scala b/test/files/run/SD-235.scala
new file mode 100644
index 0000000000..eb79c6fe71
--- /dev/null
+++ b/test/files/run/SD-235.scala
@@ -0,0 +1,39 @@
+class C {
+  var ORef: Object = null
+  def test = {
+    object O {
+      assert(!Thread.holdsLock(C.this))
+      assert(Thread.holdsLock(ORef))
+    }
+    val captor = new { def oh = O }
+    val refField = captor.getClass.getDeclaredFields.last
+    refField.setAccessible(true)
+    assert(refField.getType.toString.contains("LazyRef"), refField)
+    ORef = refField.get(captor)
+    O
+  }
+}
+
+class D {
+  var ORef: Object = null
+  def test = {
+    lazy val O = {
+      assert(!Thread.holdsLock(D.this))
+      assert(Thread.holdsLock(ORef))
+      "O"
+    }
+    val captor = new { def oh = O }
+    val refField = captor.getClass.getDeclaredFields.last
+    refField.setAccessible(true)
+    assert(refField.getType.toString.contains("LazyRef"), refField)
+    ORef = refField.get(captor)
+    O
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    new C().test
+    new D().test
+  }
+}
diff --git a/test/files/run/delambdafy_t6028.check b/test/files/run/delambdafy_t6028.check
index 7b319c92dd..86cb1d5e97 100644
--- a/test/files/run/delambdafy_t6028.check
+++ b/test/files/run/delambdafy_t6028.check
@@ -15,7 +15,7 @@ package <empty> {
       }
     };
     def bar(barParam: String): Object = {
-      @volatile var MethodLocalObject$module: runtime.VolatileObjectRef = scala.runtime.VolatileObjectRef.zero();
+      lazy <artifact> val MethodLocalObject$module: scala.runtime.LazyRef = new scala.runtime.LazyRef();
       T.this.MethodLocalObject$1(barParam, MethodLocalObject$module)
     };
     def tryy(tryyParam: String): Function0 = {
@@ -42,13 +42,14 @@ package <empty> {
       <synthetic> <stable> <artifact> def $outer(): T = MethodLocalObject$2.this.$outer;
       <synthetic> <stable> <artifact> def $outer(): T = MethodLocalObject$2.this.$outer
     };
-    final private[this] def MethodLocalObject$lzycompute$1(barParam$1: String, MethodLocalObject$module$1: runtime.VolatileObjectRef): Unit = T.this.synchronized[Unit](if (MethodLocalObject$module$1.elem.$asInstanceOf[T#MethodLocalObject$2.type]().eq(null))
-      MethodLocalObject$module$1.elem = new T#MethodLocalObject$2.type(T.this, barParam$1));
-    final <stable> private[this] def MethodLocalObject$1(barParam$1: String, MethodLocalObject$module$1: runtime.VolatileObjectRef): T#MethodLocalObject$2.type = {
-      if (MethodLocalObject$module$1.elem.$asInstanceOf[T#MethodLocalObject$2.type]().eq(null))
-        T.this.MethodLocalObject$lzycompute$1(barParam$1, MethodLocalObject$module$1);
-      (MethodLocalObject$module$1.elem.$asInstanceOf[T#MethodLocalObject$2.type](): T#MethodLocalObject$2.type)
-    };
+    final <artifact> private[this] def MethodLocalObject$lzycompute$1(barParam$1: String, MethodLocalObject$module$1: scala.runtime.LazyRef): T#MethodLocalObject$2.type = MethodLocalObject$module$1.synchronized[T#MethodLocalObject$2.type](if (MethodLocalObject$module$1.initialized())
+      MethodLocalObject$module$1.value().$asInstanceOf[T#MethodLocalObject$2.type]()
+    else
+      MethodLocalObject$module$1.initialize(new T#MethodLocalObject$2.type(T.this, barParam$1)).$asInstanceOf[T#MethodLocalObject$2.type]());
+    final private[this] def MethodLocalObject$1(barParam$1: String, MethodLocalObject$module$1: scala.runtime.LazyRef): T#MethodLocalObject$2.type = if (MethodLocalObject$module$1.initialized())
+      MethodLocalObject$module$1.value().$asInstanceOf[T#MethodLocalObject$2.type]()
+    else
+      T.this.MethodLocalObject$lzycompute$1(barParam$1, MethodLocalObject$module$1);
     final <artifact> private[this] def $anonfun$tryy$1(tryyParam$1: String, tryyLocal$1: runtime.ObjectRef): Unit = try {
       tryyLocal$1.elem = tryyParam$1
     } finally ()
diff --git a/test/files/run/local_obj.scala b/test/files/run/local_obj.scala
new file mode 100644
index 0000000000..25123f7078
--- /dev/null
+++ b/test/files/run/local_obj.scala
@@ -0,0 +1,9 @@
+class C {
+  val z = 2
+  def mod = { object x { val y = z } ; x.y }
+}
+
+object Test extends App {
+  val c = new C
+  assert(c.mod == c.z, s"${c.mod} != ${c.z}")
+}
diff --git a/test/files/run/t6028.check b/test/files/run/t6028.check
index 903ea3b753..05634fa8eb 100644
--- a/test/files/run/t6028.check
+++ b/test/files/run/t6028.check
@@ -15,7 +15,7 @@ package <empty> {
       }
     };
     def bar(barParam: Int): Object = {
-      @volatile var MethodLocalObject$module: runtime.VolatileObjectRef = scala.runtime.VolatileObjectRef.zero();
+      lazy <artifact> val MethodLocalObject$module: scala.runtime.LazyRef = new scala.runtime.LazyRef();
       T.this.MethodLocalObject$1(barParam, MethodLocalObject$module)
     };
     def tryy(tryyParam: Int): Function0 = {
@@ -54,13 +54,14 @@ package <empty> {
       <synthetic> <stable> <artifact> def $outer(): T = MethodLocalObject$2.this.$outer;
       <synthetic> <stable> <artifact> def $outer(): T = MethodLocalObject$2.this.$outer
     };
-    final private[this] def MethodLocalObject$lzycompute$1(barParam$1: Int, MethodLocalObject$module$1: runtime.VolatileObjectRef): Unit = T.this.synchronized[Unit](if (MethodLocalObject$module$1.elem.$asInstanceOf[T#MethodLocalObject$2.type]().eq(null))
-      MethodLocalObject$module$1.elem = new T#MethodLocalObject$2.type(T.this, barParam$1));
-    final <stable> private[this] def MethodLocalObject$1(barParam$1: Int, MethodLocalObject$module$1: runtime.VolatileObjectRef): T#MethodLocalObject$2.type = {
-      if (MethodLocalObject$module$1.elem.$asInstanceOf[T#MethodLocalObject$2.type]().eq(null))
-        T.this.MethodLocalObject$lzycompute$1(barParam$1, MethodLocalObject$module$1);
-      (MethodLocalObject$module$1.elem.$asInstanceOf[T#MethodLocalObject$2.type](): T#MethodLocalObject$2.type)
-    };
+    final <artifact> private[this] def MethodLocalObject$lzycompute$1(barParam$1: Int, MethodLocalObject$module$1: scala.runtime.LazyRef): T#MethodLocalObject$2.type = MethodLocalObject$module$1.synchronized[T#MethodLocalObject$2.type](if (MethodLocalObject$module$1.initialized())
+      MethodLocalObject$module$1.value().$asInstanceOf[T#MethodLocalObject$2.type]()
+    else
+      MethodLocalObject$module$1.initialize(new T#MethodLocalObject$2.type(T.this, barParam$1)).$asInstanceOf[T#MethodLocalObject$2.type]());
+    final private[this] def MethodLocalObject$1(barParam$1: Int, MethodLocalObject$module$1: scala.runtime.LazyRef): T#MethodLocalObject$2.type = if (MethodLocalObject$module$1.initialized())
+      MethodLocalObject$module$1.value().$asInstanceOf[T#MethodLocalObject$2.type]()
+    else
+      T.this.MethodLocalObject$lzycompute$1(barParam$1, MethodLocalObject$module$1);
     @SerialVersionUID(value = 0) final <synthetic> class $anonfun$tryy$1 extends scala.runtime.AbstractFunction0$mcV$sp with Serializable {
       def <init>($outer: T, tryyParam$1: Int, tryyLocal$1: runtime.IntRef): <$anon: Function0> = {
         $anonfun$tryy$1.super.<init>();
diff --git a/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala b/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala
index 8861577366..5cedc483cd 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala
@@ -105,10 +105,10 @@ class ScalaInlineInfoTest extends BytecodeTesting {
         ("x4$(LT;)I",                                                  MethodInlineInfo(true ,false,false)),
         ("x5()I",                                                     MethodInlineInfo(true, false,false)),
         ("x5$(LT;)I",                                                  MethodInlineInfo(true ,false,false)),
-        ("L$1(Lscala/runtime/VolatileObjectRef;)LT$L$2$;",            MethodInlineInfo(true, false,false)),
+        ("L$1(Lscala/runtime/LazyRef;)LT$L$2$;",                      MethodInlineInfo(true, false,false)),
         ("nest$1()I",                                                 MethodInlineInfo(true, false,false)),
         ("$init$(LT;)V",                                              MethodInlineInfo(true,false,false)),
-        ("L$lzycompute$1(Lscala/runtime/VolatileObjectRef;)V",        MethodInlineInfo(true,false,false))
+        ("L$lzycompute$1(Lscala/runtime/LazyRef;)LT$L$2$;",           MethodInlineInfo(true,false,false))
       ),
       None // warning
     )