Isolate the state of local name generation in a class.

Author: sjrd

src/dotty/tools/backend/sjs/JSCodeGen.scala

@@ -56,12 +56,13 @@ class JSCodeGen()(implicit ctx: Context) {
   private val primitives = new JSPrimitives(ctx)
 
   private val positionConversions = new JSPositions()
-  import positionConversions._
+  import positionConversions.{pos2irPos, implicitPos2irPos}
 
   // Some state --------------------------------------------------------------
 
   private val currentClassSym          = new ScopedVar[Symbol]
   private val currentMethodSym         = new ScopedVar[Symbol]
+  private val localNames               = new ScopedVar[LocalNameGenerator]
   /*
   private val thisLocalVarIdent        = new ScopedVar[Option[js.Ident]](None)
   private val fakeTailJumpParamRepl    = new ScopedVar[(Symbol, Symbol)]((NoSymbol, NoSymbol))
@@ -74,6 +75,9 @@ class JSCodeGen()(implicit ctx: Context) {
   private val paramAccessorLocals      = new ScopedVar(Map.empty[Symbol, js.ParamDef])
   */
 
+  /** Implicitly materializes the current local name generator. */
+  private implicit def implicitLocalNames: LocalNameGenerator = localNames.get
+
   private var isModuleInitialized: Boolean = false // see genApply for super calls
 
   //val countsOfReturnsToMatchEnd = mutable.Map.empty[Symbol, Int]
@@ -605,7 +609,9 @@ class JSCodeGen()(implicit ctx: Context) {
   // Generate a method -------------------------------------------------------
 
   private def genMethod(dd: DefDef): Option[js.MethodDef] = {
-    withNewLocalNameScope {
+    withScopedVars(
+        localNames := new LocalNameGenerator
+    ) {
       genMethodWithCurrentLocalNameScope(dd)
     }
   }

src/dotty/tools/backend/sjs/JSEncoding.scala

@@ -54,42 +54,44 @@ object JSEncoding {
 
   // Fresh local name generator ----------------------------------------------
 
-  private val usedLocalNames = new ScopedVar[mutable.Set[String]]
-  private val localSymbolNames = new ScopedVar[mutable.Map[Symbol, String]]
-  private val isReserved =
-    Set("arguments", "eval", ScalaJSEnvironmentName)
-
-  def withNewLocalNameScope[A](body: => A): A =
-    withScopedVars(
-        usedLocalNames := mutable.Set.empty,
-        localSymbolNames := mutable.Map.empty
-    )(body)
-
-  private def freshName(base: String = "x"): String = {
-    var suffix = 1
-    var longName = base
-    while (usedLocalNames(longName) || isReserved(longName)) {
-      suffix += 1
-      longName = base+"$"+suffix
-    }
-    usedLocalNames += longName
-    mangleJSName(longName)
-  }
+  class LocalNameGenerator {
+    import LocalNameGenerator._
+
+    private val usedLocalNames = mutable.Set.empty[String]
+    private val localSymbolNames = mutable.Map.empty[Symbol, String]
+
+    def localSymbolName(sym: Symbol)(implicit ctx: Context): String =
+      localSymbolNames.getOrElseUpdate(sym, freshName(sym.name.toString))
+
+    def freshLocalIdent()(implicit pos: ir.Position): js.Ident =
+      js.Ident(freshName(), None)
 
-  def freshLocalIdent()(implicit pos: ir.Position): js.Ident =
-    js.Ident(freshName(), None)
+    def freshLocalIdent(base: String)(implicit pos: ir.Position): js.Ident =
+      js.Ident(freshName(base), Some(base))
 
-  def freshLocalIdent(base: String)(implicit pos: ir.Position): js.Ident =
-    js.Ident(freshName(base), Some(base))
+    private def freshName(base: String = "x"): String = {
+      var suffix = 1
+      var longName = base
+      while (usedLocalNames(longName) || isReserved(longName)) {
+        suffix += 1
+        longName = base+"$"+suffix
+      }
+      usedLocalNames += longName
+      mangleJSName(longName)
+    }
+  }
 
-  private def localSymbolName(sym: Symbol)(implicit ctx: Context): String =
-    localSymbolNames.getOrElseUpdate(sym, freshName(sym.name.toString))
+  private object LocalNameGenerator {
+    private val isReserved =
+      Set("arguments", "eval", ScalaJSEnvironmentName)
+  }
 
   // Encoding methods ----------------------------------------------------------
 
-  def encodeLabelSym(sym: Symbol)(implicit ctx: Context, pos: ir.Position): js.Ident = {
+  def encodeLabelSym(sym: Symbol)(
+      implicit ctx: Context, pos: ir.Position, localNames: LocalNameGenerator): js.Ident = {
     require(sym.is(Flags.Label), "encodeLabelSym called with non-label symbol: " + sym)
-    js.Ident(localSymbolName(sym), Some(sym.unexpandedName.decoded))
+    js.Ident(localNames.localSymbolName(sym), Some(sym.unexpandedName.decoded))
   }
 
   private def allRefClasses(implicit ctx: Context): Set[Symbol] = {
@@ -190,10 +192,10 @@ object JSEncoding {
   }
 
   def encodeLocalSym(sym: Symbol)(
-      implicit ctx: Context, pos: ir.Position): js.Ident = {
+      implicit ctx: Context, pos: ir.Position, localNames: LocalNameGenerator): js.Ident = {
     require(!sym.owner.isClass && sym.isTerm && !sym.is(Flags.Method) && !sym.is(Flags.Module),
         "encodeLocalSym called with non-local symbol: " + sym)
-    js.Ident(localSymbolName(sym), Some(sym.unexpandedName.decoded))
+    js.Ident(localNames.localSymbolName(sym), Some(sym.unexpandedName.decoded))
   }
 
   def foreignIsImplClass(sym: Symbol)(implicit ctx: Context): Boolean =