Reapply "Added for-loop variable tracking and regular closures/initializers captured variable track…

pkg/compiler/lib/src/closure.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'common/names.dart' show Identifiers;
 import 'common/resolution.dart' show ParsingContext, Resolution;
 import 'common/tasks.dart' show CompilerTask, Measurer;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
 import 'constants/expressions.dart';
@@ skipping 66 matching lines @@
   /// Returns true if this [variable] is used inside a `try` block or a `sync*`
   /// generator (this is important to know because boxing/redirection needs to
   /// happen for those local variables).
   ///
   /// Variables that are used in a try must be treated as boxed because the
   /// control flow can be non-linear.
   ///
   /// Also parameters to a `sync*` generator must be boxed, because of the way
   /// we rewrite sync* functions. See also comments in
   /// [ClosureClassMap.useLocal].
-  bool variableIsUsedInTryOrSync(Local variable) => false;
+  bool localIsUsedInTryOrSync(Local variable) => false;
 
   /// Loop through each variable that has been defined in this scope, modified
   /// anywhere (this scope or another scope) and used in another scope. Because
   /// it is used in another scope, these variables need to be "boxed", creating
   /// a thin wrapper around accesses to these variables so that accesses get
-  /// the correct updated value. The variables in variablesUsedInTryOrSync may
+  /// the correct updated value. The variables in localsUsedInTryOrSync may
   /// be included in this set.
   ///
   /// In the case of loops, this is the set of iteration variables (or any
   /// variables declared in the for loop expression (`for (...here...)`) that
   /// need to be boxed to snapshot their value.
   void forEachBoxedVariable(f(Local local, FieldEntity field)) {}
 
   /// True if [variable] has been mutated and is also used in another scope.
   bool isBoxed(Local variable) => false;
-
-  /// True if this scope declares any variables that need to be boxed.
-  bool get hasBoxedVariables => false;
 }
 
 /// Class representing the usage of a scope that has been captured in the
 /// context of a closure.
 class ClosureScope extends ScopeInfo {
   const ClosureScope();
 
   /// If true, this closure accesses a variable that was defined in an outside
   /// scope and this variable gets modified at some point (sometimes we say that
   /// variable has been "captured"). In this situation, access to this variable
@@ skipping 18 matching lines @@
 ///     var lst = [];
 ///     for (int i = 0; i < 5; i++) lst.add(()=>i);
 ///     var result = list.map((f) => f()).toList();
 ///
 /// `result` will be [0, 1, 2, 3, 4], whereas were this JS code
 /// the result would be [5, 5, 5, 5, 5]. Because of this difference we need to
 /// create a closure for these sorts of loops to capture the variable's value at
 /// each iteration, by boxing the iteration variable[s].
 class LoopClosureScope extends ClosureScope {
   const LoopClosureScope();
+
+  /// True if this loop scope declares in the first part of the loop
+  /// `for (<here>;...;...)` any variables that need to be boxed.
+  bool get hasBoxedLoopVariables => false;
+
+  /// The set of iteration variables (or variables declared in the for loop
+  /// expression (`for (<here>; ... ; ...)`) that need to be boxed to snapshot
+  /// their value. These variables are also included in the set of
+  /// `forEachBoxedVariable` method. The distinction between these two sets is
+  /// in this example:
+  ///
+  ///     run(f) => f();
+  ///     var a;
+  ///     for (int i = 0; i < 3; i++) {
+  ///       var b = 3;
+  ///       a = () => b = i;
+  ///     }
+  ///
+  /// `i` would be a part of the boxedLoopVariables AND boxedVariables, but b
+  /// would only be a part of boxedVariables.
+  List<Local> get boxedLoopVariables => const <Local>[];
 }
 
 /// Class that describes the actual mechanics of how the converted, rewritten
 /// closure is implemented. For example, for the following closure (named foo
 /// for convenience):
 ///
 ///   var foo = (x) => y + x;
 ///
 /// We would produce the following class to control access to these variables in
 /// the following way (modulo naming of variables, assuming that y is modified
@@ skipping 486 matching lines @@
   // Otherwise contains the empty List.
   List<Local> boxedLoopVariables = const <Local>[];
 
   ClosureScopeImpl(this.boxElement, this.capturedVariables);
 
   Local get context => boxElement;
 
   bool get requiresContextBox => capturedVariables.keys.isNotEmpty;
 
   void forEachBoxedVariable(f(Local local, FieldEntity field)) {
-    if (capturedVariables.isNotEmpty) {
-      capturedVariables.forEach(f);
-    } else {
-      for (Local l in boxedLoopVariables) {
-        // The boxes for loop variables are constructed on-demand per-iteration
-        // in the locals handler.
-        f(l, null);
-      }
-    }
+    capturedVariables.forEach(f);
   }
 
-  bool get hasBoxedVariables => !capturedVariables.isEmpty;
+  bool get hasBoxedLoopVariables => boxedLoopVariables.isNotEmpty;
 
   bool isBoxed(Local variable) {
     return capturedVariables.containsKey(variable);
   }
 
   void forEachCapturedVariable(
       f(LocalVariableElement variable, BoxFieldElement boxField)) {
     capturedVariables.forEach(f);
   }
 
   // Should not be called. Added to make the new interface happy.
-  bool variableIsUsedInTryOrSync(Local variable) =>
-      throw new UnsupportedError("ClosureScopeImpl.variableIsUsedInTryOrSync");
+  bool localIsUsedInTryOrSync(Local variable) =>
+      throw new UnsupportedError("ClosureScopeImpl.localIsUsedInTryOrSync");
 
   // Should not be called. Added to make the new interface happy.
   Local get thisLocal =>
       throw new UnsupportedError("ClosureScopeImpl.thisLocal");
 
   String toString() {
     String separator = '';
     StringBuffer sb = new StringBuffer();
     sb.write('ClosureScopeImpl(');
     if (boxElement != null) {
@@ skipping 49 matching lines @@
   /// Set of [variable]s referenced in this scope that are used inside a
   /// `try` block or a `sync*` generator (this is important to know because
   /// boxing/redirection needs to happen for those local variables).
   ///
   /// Variables that are used in a try must be treated as boxed because the
   /// control flow can be non-linear.
   ///
   /// Also parameters to a `sync*` generator must be boxed, because of the way
   /// we rewrite sync* functions. See also comments in [useLocal].
   // TODO(johnniwinther): Add variables to this only if the variable is mutated.
-  final Set<Local> variablesUsedInTryOrSync = new Set<Local>();
+  final Set<Local> localsUsedInTryOrSync = new Set<Local>();
 
   ClosureClassMap(this.closureEntity, this.closureClassEntity, this.callMethod,
       this.thisLocal);
 
-  bool get hasBoxedVariables =>
-      throw new UnsupportedError("ClosureClassMap.hasBoxedVariables");
-
   List<Local> get createdFieldEntities {
     List<Local> fields = <Local>[];
     if (closureClassEntity == null) return const <Local>[];
     closureClassEntity.closureFields.forEach((field) {
       fields.add(field.local);
     });
     return fields;
   }
 
   void addFreeVariable(Local element) {
     assert(freeVariableMap[element] == null);
     freeVariableMap[element] = null;
   }
 
   Iterable<Local> get freeVariables => freeVariableMap.keys;
 
   bool isFreeVariable(Local element) {
     return freeVariableMap.containsKey(element);
   }
 
   void forEachFreeVariable(f(Local variable, FieldEntity field)) {
     freeVariableMap.forEach(f);
   }
 
   FieldEntity get thisFieldEntity => freeVariableMap[thisLocal];
 
-  bool variableIsUsedInTryOrSync(Local variable) =>
-      variablesUsedInTryOrSync.contains(variable);
+  bool localIsUsedInTryOrSync(Local variable) =>
+      localsUsedInTryOrSync.contains(variable);
 
   Local getLocalVariableForClosureField(ClosureFieldElement field) {
     return field.local;
   }
 
   bool get isClosure => closureEntity != null;
 
   bool capturingScopesBox(Local variable) {
     return capturingScopes.values.any((scope) {
       return scope.boxedLoopVariables.contains(variable);
@@ skipping 228 matching lines @@
 
     if (insideClosure && !inCurrentContext(variable)) {
       closureData.addFreeVariable(variable);
     } else if (inTryStatement) {
       // Don't mark the this-element or a self-reference. This would complicate
       // things in the builder.
       // Note that nested (named) functions are immutable.
       if (variable != closureData.thisLocal &&
           variable != closureData.closureEntity &&
           variable is! TypeVariableLocal) {
-        closureData.variablesUsedInTryOrSync.add(variable);
+        closureData.localsUsedInTryOrSync.add(variable);
       }
     } else if (variable is LocalParameterElement &&
         variable.functionDeclaration.asyncMarker == AsyncMarker.SYNC_STAR) {
       // Parameters in a sync* function are shared between each Iterator created
       // by the Iterable returned by the function, therefore they must be boxed.
-      closureData.variablesUsedInTryOrSync.add(variable);
+      closureData.localsUsedInTryOrSync.add(variable);
     }
   }
 
   void useTypeVariableAsLocal(ResolutionTypeVariableType typeVariable) {
     useLocal(new TypeVariableLocal(
         typeVariable, outermostElement, outermostElement.memberContext));
   }
 
   void declareLocal(LocalVariableElement element) {
     scopeVariables.add(element);
@@ skipping 480 matching lines @@
 ///
 /// Move the below classes to a JS model eventually.
 ///
 abstract class JSEntity implements MemberEntity {
   Local get declaredEntity;
 }
 
 abstract class PrivatelyNamedJSEntity implements JSEntity {
   Entity get rootOfScope;
 }