Support name table sharing across Global instances

  - Add UI to enable name table sharing
  - Expose name table caching through PipelineMain

Author: retronym

src/compiler/scala/tools/nsc/Global.scala

@@ -23,6 +23,7 @@ import io.{AbstractFile, Path, SourceReader}
 import reporters.Reporter
 import util.{ClassPath, returning}
 import scala.reflect.ClassTag
+import scala.reflect.internal.{NameTable, Names}
 import scala.reflect.internal.util.{BatchSourceFile, FreshNameCreator, NoSourceFile, ScalaClassLoader, ScriptSourceFile, SourceFile, StatisticsStatics}
 import scala.reflect.internal.pickling.PickleBuffer
 import symtab.{Flags, SymbolTable, SymbolTrackers}
@@ -35,7 +36,6 @@ import transform.patmat.PatternMatching
 import transform._
 import backend.{JavaPlatform, ScalaPrimitives}
 import backend.jvm.{BackendStats, GenBCode}
-import scala.concurrent.Future
 import scala.language.postfixOps
 import scala.tools.nsc.ast.{TreeGen => AstTreeGen}
 import scala.tools.nsc.classpath._
@@ -59,6 +59,13 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
 
   override def isCompilerUniverse = true
   override val useOffsetPositions = !currentSettings.Yrangepos
+  override protected def newNameTable: NameTable[this.type] = {
+    if (currentSettings.YcacheNameTable) {
+      val NoFiles = Nil
+      Global.nameTableCache.getOrCreate(NoFiles, () => new NameTable[Names.dummyNamesInstance.type](synchronizeNames = true, Names.dummyNamesInstance), closeableRegistry, checkStamps = true).asInstanceOf[NameTable[this.type]]
+    }
+    else super.newNameTable
+  }
 
   type RuntimeClass = java.lang.Class[_]
   implicit val RuntimeClassTag: ClassTag[RuntimeClass] = ClassTag[RuntimeClass](classOf[RuntimeClass])
@@ -1736,4 +1743,7 @@ object Global {
     override def keepsTypeParams = false
     def run() { throw new Error("InitPhase.run") }
   }
+
+  // TODO factor reference counting caching out of FileBasedCache for use in spots like this.
+  private val nameTableCache = new FileBasedCache[NameTable[_]]
 }

src/compiler/scala/tools/nsc/PipelineMain.scala

@@ -382,10 +382,13 @@ class PipelineMainClass(label: String, parallelism: Int, strategy: BuildStrategy
 
     val cacheMacro = java.lang.Boolean.getBoolean("scala.pipeline.cache.macro.classloader")
     val cachePlugin = java.lang.Boolean.getBoolean("scala.pipeline.cache.plugin.classloader")
+    val cacheNameTable = java.lang.Boolean.getBoolean("scala.pipeline.cache.name.table")
     if (cacheMacro)
       command.settings.YcacheMacroClassLoader.value = "always"
     if (cachePlugin)
       command.settings.YcachePluginClassLoader.value = "always"
+    if (cacheNameTable)
+      command.settings.YcacheNameTable.value = true
 
     if (strategy != Traditional) {
       command.settings.YpickleJava.value = true

src/compiler/scala/tools/nsc/settings/ScalaSettings.scala

@@ -244,6 +244,7 @@ trait ScalaSettings extends AbsScalaSettings
   val YpartialUnification = BooleanSetting ("-Ypartial-unification", "Enable partial unification in type constructor inference")
   val Yvirtpatmat     = BooleanSetting    ("-Yvirtpatmat", "Enable pattern matcher virtualization")
   val Youtline        = BooleanSetting    ("-Youtline", "Don't compile method bodies. Use together with `-Ystop-afer:pickler to generate the pickled signatures for all source files.").internalOnly()
+  val YcacheNameTable = BooleanSetting  ("-Ycache-name-table", "Share a single name table for concurrently running instances of the compiler")
 
   val exposeEmptyPackage = BooleanSetting ("-Yexpose-empty-package", "Internal only: expose the empty package.").internalOnly()
   val Ydelambdafy        = ChoiceSetting  ("-Ydelambdafy", "strategy", "Strategy used for translating lambdas into JVM code.", List("inline", "method"), "method")