Implement try/catch without finally, and without type checks.

frog/leg/ssa/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.
 
 class ClosureFieldElement extends Element {
   ClosureFieldElement(SourceString name, ClassElement enclosing)
       : super(name, ElementKind.FIELD, enclosing);
 
   bool isInstanceMember() => true;
   bool isAssignable() => false;
@@ skipping 26 matching lines @@
   // boxes) to their boxElement.
   final Map<Element, Element> capturedFieldMapping;
 
   // Maps scopes ([Loop] and [FunctionExpression] nodes) to their
   // [ClosureScope] which contains their box and the
   // captured variables that are stored in the box.
   // This map will be empty if the method/closure of this [ClosureData] does not
   // contain any nested closure.
   final Map<Node, ClosureScope> capturingScopes;
 
+  final Set<Element> usedVariablesInTry;
+
   ClosureData(this.globalizedClosureElement, this.callElement)
       : this.freeVariableMapping = new Map<Element, Element>(),
         this.capturedFieldMapping = new Map<Element, Element>(),
-        this.capturingScopes = new Map<Node, ClosureScope>();
+        this.capturingScopes = new Map<Node, ClosureScope>(),
+        this.usedVariablesInTry = new Set<Element>();
 }
 
 Map<Node, ClosureData> _closureDataCache;
 Map<Node, ClosureData> get closureDataCache() {
   if (_closureDataCache === null) {
     _closureDataCache = new HashMap<Node, ClosureData>();
   }
   return _closureDataCache;
 }
 
 class ClosureTranslator extends AbstractVisitor {
   final Compiler compiler;
   final TreeElements elements;
   int boxCounter = 0;
+  bool inTryCatchOrFinally = false;
 
   // Map of captured variables. Initially they will map to themselves. If
   // a variable needs to be boxed then the scope declaring the variable
   // will update this mapping.
   Map<Element, Element> capturedVariableMapping;
   // List of encountered closures.
   List<FunctionExpression> closures;
 
   // The variables that have been declared in the current scope.
   List<Element> scopeVariables;
@@ skipping 65 matching lines @@
         freeVariableMapping[boxElement] = fieldElement;
       }
     }
   }
 
   void useLocal(Element element) {
     if (element.enclosingElement != currentFunctionElement) {
       assert(closureData.freeVariableMapping[element] == null ||
              closureData.freeVariableMapping[element] == element);
       closureData.freeVariableMapping[element] = element;
+    } else if (inTryCatchOrFinally) {
+      // TODO(ngeoffray): only do this if the variable is mutated.
+      closureData.usedVariablesInTry.add(element);
     }
   }
 
   void declareLocal(Element element) {
     scopeVariables.add(element);
   }
 
   visit(Node node) => node.accept(this);
 
   visitNode(Node node) => node.visitChildren(this);
@@ skipping 140 matching lines @@
       useLocal(element);
     }
 
     // If we just visited a closure we declare it. This is not always correct
     // since some closures are used as expressions and don't introduce any
     // name. But in this case the added local is simply not used.
     if (savedInsideClosure) {
       declareLocal(elements[node]);
     }
   }
+
+  visitTryStatement(TryStatement node) {
+    // TODO(ngeoffray): implement finer grain state.
+    inTryCatchOrFinally = true;
+    node.visitChildren(this);
+    inTryCatchOrFinally = false;
+  }
 }