Add @sharable annotation

Add @sharable annotation for classes and vals that are presumed
to be safely sharable between threads.

Also: Document CtxLazy.

src/dotty/tools/dotc/Bench.scala

@@ -10,7 +10,7 @@ import reporting.Reporter
 
 object Bench extends Driver {
 
-  private var numRuns = 1
+  @sharable private var numRuns = 1
 
   def newCompiler(): Compiler = new Compiler
 

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

@@ -209,7 +209,7 @@ object desugar {
     else tdef
   }
 
-  private val synthetic = Modifiers(Synthetic)
+  @sharable private val synthetic = Modifiers(Synthetic)
 
   private def toDefParam(tparam: TypeDef): TypeDef =
     tparam.withFlags(Param)

src/dotty/tools/dotc/ast/Trees.scala

@@ -1,4 +1,5 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package ast
 
 import core._
@@ -26,7 +27,7 @@ object Trees {
   type Untyped = Null
 
   /** The total number of created tree nodes, maintained if Stats.enabled */
-  var ntrees = 0
+  @sharable var ntrees = 0
 
   /** Modifiers and annotations for definitions
    *  @param flags          The set flags
@@ -68,7 +69,7 @@ object Trees {
     def tokenPos: Seq[(Token, Position)] = ???
   }
 
-  private var nextId = 0 // for debugging
+  @sharable private var nextId = 0 // for debugging
 
   type LazyTree = AnyRef     /* really: Tree | Lazy[Tree] */
   type LazyTreeList = AnyRef /* really: List[Tree] | Lazy[List[Tree]] */
@@ -723,9 +724,9 @@ object Trees {
     setMods(Modifiers[T](PrivateLocal))
   }
 
-  val theEmptyTree: Thicket[Type] = Thicket(Nil)
-  val theEmptyValDef = new EmptyValDef[Type]
-  val theEmptyModifiers = new Modifiers()
+  @sharable val theEmptyTree: Thicket[Type] = Thicket(Nil)
+  @sharable val theEmptyValDef = new EmptyValDef[Type]
+  @sharable val theEmptyModifiers = new Modifiers()
 
   def genericEmptyValDef[T >: Untyped]: ValDef[T]       = theEmptyValDef.asInstanceOf[ValDef[T]]
   def genericEmptyTree[T >: Untyped]: Thicket[T]        = theEmptyTree.asInstanceOf[Thicket[T]]
@@ -845,9 +846,9 @@ object Trees {
     type Annotated = Trees.Annotated[T]
     type Thicket = Trees.Thicket[T]
 
-    val EmptyTree: Thicket = genericEmptyTree
-    val EmptyValDef: ValDef = genericEmptyValDef
-    val EmptyModifiers: Modifiers = genericEmptyModifiers
+    @sharable val EmptyTree: Thicket = genericEmptyTree
+    @sharable val EmptyValDef: ValDef = genericEmptyValDef
+    @sharable val EmptyModifiers: Modifiers = genericEmptyModifiers
 
     // ----- Auxiliary creation methods ------------------
 

src/dotty/tools/dotc/config/Properties.scala

@@ -12,7 +12,7 @@ object Properties extends PropertiesTrait {
 
   /** Scala manifest attributes.
    */
-  val ScalaCompilerVersion = new AttributeName("Scala-Compiler-Version")
+  @sharable val ScalaCompilerVersion = new AttributeName("Scala-Compiler-Version")
 }
 
 trait PropertiesTrait {
@@ -23,7 +23,7 @@ trait PropertiesTrait {
   protected val propFilename = "/" + propCategory + ".properties"
 
   /** The loaded properties */
-  protected lazy val scalaProps: java.util.Properties = {
+  @sharable protected lazy val scalaProps: java.util.Properties = {
     val props = new java.util.Properties
     val stream = pickJarBasedOn getResourceAsStream propFilename
     if (stream ne null)

src/dotty/tools/dotc/config/ScalaVersion.scala

@@ -1,6 +1,7 @@
 /* @author  James Iry
  */
-package dotty.tools.dotc.config
+package dotty.tools
+package dotc.config
 
 import scala.util.{Try, Success, Failure}
 
@@ -15,7 +16,7 @@ sealed abstract class ScalaVersion extends Ordered[ScalaVersion] {
 /**
  * A scala version that sorts higher than all actual versions
  */
-case object NoScalaVersion extends ScalaVersion {
+@sharable case object NoScalaVersion extends ScalaVersion {
   def unparse = "none"
 
   def compare(that: ScalaVersion): Int = that match {

src/dotty/tools/dotc/core/Contexts.scala

@@ -28,6 +28,7 @@ import printing._
 import config.{Settings, ScalaSettings, Platform, JavaPlatform}
 import language.implicitConversions
 import DenotTransformers.DenotTransformer
+
 object Contexts {
 
   /** A context is passed basically everywhere in dotc.
@@ -473,7 +474,7 @@ object Contexts {
     gadt = new GADTMap(SimpleMap.Empty)
   }
 
-  object NoContext extends Context {
+  @sharable object NoContext extends Context {
     lazy val base = unsupported("base")
     override val implicits: ContextualImplicits = new ContextualImplicits(Nil, null)(this)
   }
@@ -620,7 +621,7 @@ object Contexts {
     /** implicit conversion that injects all ContextBase members into a context */
     implicit def toBase(ctx: Context): ContextBase = ctx.base
 
-    val theBase = new ContextBase // !!! DEBUG, so that we can use a minimal context for reporting even in code that normally cannot access a context
+    // @sharable val theBase = new ContextBase // !!! DEBUG, so that we can use a minimal context for reporting even in code that normally cannot access a context
   }
 
   /** Info that changes on each compiler run */

src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1,4 +1,5 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package core
 
 import Periods._, Contexts._, Symbols._, Denotations._, Names._, NameOps._, Annotations._
@@ -1713,8 +1714,8 @@ object SymDenotations {
     validFor = Period.allInRun(NoRunId) // will be brought forward automatically
   }
 
-  val NoDenotation = new NoDenotation
-  val NotDefinedHereDenotation = new NoDenotation
+  @sharable val NoDenotation = new NoDenotation
+  @sharable val NotDefinedHereDenotation = new NoDenotation
 
   // ---- Completion --------------------------------------------------------
 
@@ -1757,7 +1758,7 @@ object SymDenotations {
   val NoSymbolFn = (ctx: Context) => NoSymbol
 
   /** A missing completer */
-  class NoCompleter extends LazyType {
+  @sharable class NoCompleter extends LazyType {
     def complete(denot: SymDenotation)(implicit ctx: Context): Unit = unsupported("complete")
   }
 

src/dotty/tools/dotc/core/TypeOps.scala

@@ -1,4 +1,5 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package core
 
 import Contexts._, Types._, Symbols._, Names._, Flags._, Scopes._
@@ -572,5 +573,5 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
 
 object TypeOps {
   val emptyDNF = (Nil, Set[Name]()) :: Nil
-  var track = false // !!!DEBUG
+  @sharable var track = false // !!!DEBUG
 }

src/dotty/tools/dotc/core/Types.scala

@@ -1,4 +1,5 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package core
 
 import util.common._
@@ -35,7 +36,7 @@ import language.implicitConversions
 
 object Types {
 
-  private var nextId = 0
+  @sharable private var nextId = 0
 
   /** The class of types.
    *  The principal subclasses and sub-objects are as follows:
@@ -73,6 +74,7 @@ object Types {
 
 // ----- Tests -----------------------------------------------------
 
+    // debug only: a unique identifier for a type
     val uniqId = {
       nextId = nextId + 1
 //      if (nextId == 19555)
@@ -2752,13 +2754,13 @@ object Types {
   case class ImportType(expr: Tree) extends UncachedGroundType
 
   /** Sentinel for "missing type" */
-  case object NoType extends CachedGroundType {
+  @sharable case object NoType extends CachedGroundType {
     override def exists = false
     override def computeHash = hashSeed
   }
 
   /** Missing prefix */
-  case object NoPrefix extends CachedGroundType {
+  @sharable case object NoPrefix extends CachedGroundType {
     override def computeHash = hashSeed
   }
 
@@ -2775,7 +2777,7 @@ object Types {
 
   final class CachedWildcardType(optBounds: Type) extends WildcardType(optBounds)
 
-  object WildcardType extends WildcardType(NoType) {
+  @sharable object WildcardType extends WildcardType(NoType) {
     def apply(bounds: TypeBounds)(implicit ctx: Context) = unique(new CachedWildcardType(bounds))
   }
 
@@ -2983,7 +2985,7 @@ object Types {
     }
   }
 
-  object IdentityTypeMap extends TypeMap()(NoContext) {
+  @sharable object IdentityTypeMap extends TypeMap()(NoContext) {
     override def stopAtStatic = true
     def apply(tp: Type) = tp
   }
@@ -3208,7 +3210,7 @@ object Types {
 
   // ----- Debug ---------------------------------------------------------
 
-  var debugTrace = false
+  @sharable var debugTrace = false
 
   val watchList = List[String](
   ) map (_.toTypeName)

src/dotty/tools/dotc/parsing/Parsers.scala

@@ -36,11 +36,11 @@ object Parsers {
     def nonePositive: Boolean = parCounts forall (_ <= 0)
   }
 
-  object Location extends Enumeration {
+  @sharable object Location extends Enumeration {
     val InParens, InBlock, InPattern, ElseWhere = Value
   }
 
-  object ParamOwner extends Enumeration {
+  @sharable object ParamOwner extends Enumeration {
     val Class, Type, TypeParam, Def = Value
   }
 

src/dotty/tools/dotc/transform/CheckReentrant.scala

@@ -20,7 +20,6 @@ import typer.Checking
 import Names.Name
 import NameOps._
 import StdNames._
-import util.CtxLazy
 
 
 /** The first tree transform

src/dotty/tools/dotc/transform/CtxLazy.scala

@@ -1,7 +1,15 @@
 package dotty.tools.dotc
-package util
+package transform
 import core.Contexts.Context
 
+/** Utility class for lazy values whose evaluation depends on a context.
+ *  This should be used whenever the evaluation of a lazy expression
+ *  depends on some context, but the value can be re-used afterwards
+ *  with a different context.
+ *
+ *  A typical use case is a lazy val in a phase object which exists once per root context where
+ *  the expression intiializing the lazy val depends only on the root context, but not any changes afterwards.
+ */
 class CtxLazy[T](expr: Context => T) {
   private var myValue: T = _
   private var forced = false

src/dotty/tools/dotc/transform/TreeTransform.scala

@@ -1,4 +1,5 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package transform
 
 import dotty.tools.dotc.ast.tpd
@@ -194,7 +195,7 @@ object TreeTransforms {
     }
   }
 
-  val NoTransform = new TreeTransform {
+  @sharable val NoTransform = new TreeTransform {
     def phase = unsupported("phase")
     idx = -1
   }

src/dotty/tools/dotc/typer/Implicits.scala

@@ -681,4 +681,4 @@ class TermRefSet(implicit ctx: Context) extends mutable.Traversable[TermRef] {
         f(TermRef(pre, sym))
 }
 
-object EmptyTermRefSet extends TermRefSet()(NoContext)
+@sharable object EmptyTermRefSet extends TermRefSet()(NoContext)

src/dotty/tools/dotc/typer/Inferencing.scala

@@ -257,7 +257,7 @@ trait Inferencing { this: Checking =>
 }
 
 /** An enumeration controlling the degree of forcing in "is-dully-defined" checks. */
-object ForceDegree extends Enumeration {
+@sharable object ForceDegree extends Enumeration {
   val none,           // don't force type variables
       noBottom,       // force type variables, fail if forced to Nothing or Null
       all = Value     // force type variables, don't fail

src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -151,7 +151,7 @@ object ProtoTypes {
    *  operation is further selection. In this case, the expression need not be a value.
    *  @see checkValue
    */
-  object AnySelectionProto extends SelectionProto(nme.WILDCARD, WildcardType, NoViewsAllowed)
+  @sharable object AnySelectionProto extends SelectionProto(nme.WILDCARD, WildcardType, NoViewsAllowed)
 
   /** A prototype for selections in pattern constructors */
   class UnapplySelectionProto(name: Name) extends SelectionProto(name, WildcardType, NoViewsAllowed)
@@ -308,7 +308,7 @@ object ProtoTypes {
    *
    *    [] _
    */
-  object AnyFunctionProto extends UncachedGroundType with MatchAlways
+  @sharable object AnyFunctionProto extends UncachedGroundType with MatchAlways
 
   /** Add all parameters in given polytype `pt` to the constraint's domain.
    *  If the constraint contains already some of these parameters in its domain,

src/dotty/tools/dotc/util/SourceFile.scala

@@ -131,7 +131,7 @@ case class SourceFile(file: AbstractFile, content: Array[Char]) {
   override def toString = file.toString
 }
 
-object NoSource extends SourceFile("<no source>", Nil) {
+@sharable object NoSource extends SourceFile("<no source>", Nil) {
   override def exists = false
 }
 

src/dotty/tools/dotc/util/Stats.scala

@@ -1,10 +1,11 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package util
 
 import core.Contexts._
 import collection.mutable
 
-object Stats {
+@sharable object Stats {
 
   final val enabled = true