fix temps that have the same name to have different Elements

this was happening because we picked up an == operator from analyzer's Element

also adds an assert, because I took way too much time figuring out what the heck was happening there :)

[email protected]

Review URL: https://codereview.chromium.org/1139673005

Author: John Messerly

pkg/dev_compiler/lib/src/codegen/js_codegen.dart

@@ -1172,7 +1172,7 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
       return _getTemp(element, '${name.substring(1)}');
     }
 
-    if (_isTemporary(element)) {
+    if (element is TemporaryVariableElement) {
       if (name[0] == '#') {
         return new JS.InterpolatedExpression(name.substring(1));
       } else {
@@ -1775,7 +1775,7 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     // * create a new subtype of LocalVariableElementImpl to mark a temp.
     var id =
         new SimpleIdentifier(new StringToken(TokenType.IDENTIFIER, name, -1));
-    id.staticElement = new LocalVariableElementImpl.forNode(id);
+    id.staticElement = new TemporaryVariableElement.forNode(id);
     id.staticType = type;
     return id;
   }
@@ -1802,8 +1802,6 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     return value;
   }
 
-  bool _isTemporary(Element node) => node.nameOffset == -1;
-
   /// Returns a new expression, which can be be used safely *once* on the
   /// left hand side, and *once* on the right side of an assignment.
   /// For example: `expr1[expr2] += y` can be compiled as
@@ -2619,3 +2617,13 @@ bool _isJsPeerInterface(DartObjectImpl value) =>
 // but we don't have summary support yet.
 // bool _supportJsExtensionMethod(AnnotatedNode node) =>
 //    _getAnnotation(node, "SupportJsExtensionMethod") != null;
+
+/// A special kind of element created by the compiler, signifying a temporary
+/// variable. These objects use instance equality, and should be shared
+/// everywhere in the tree where they are treated as the same variable.
+class TemporaryVariableElement extends LocalVariableElementImpl {
+  TemporaryVariableElement.forNode(Identifier name) : super.forNode(name);
+
+  int get hashCode => identityHashCode(this);
+  bool operator ==(Object other) => identical(this, other);
+}

pkg/dev_compiler/lib/src/codegen/js_names.dart

@@ -85,7 +85,10 @@ class _RenameVisitor extends VariableDeclarationVisitor {
 
   declare(Identifier node) {
     var id = identifierKey(node);
-    scope.declared.add(id);
+    var notAlreadyDeclared = scope.declared.add(id);
+    // Normal identifiers can be declared multiple times, because we don't
+    // implement block scope yet. However temps should only be declared once.
+    assert(notAlreadyDeclared || node is! TemporaryId);
     _markUsed(node, id, scope);
   }
 

pkg/dev_compiler/test/codegen/expect/try_catch.js

@@ -53,10 +53,10 @@ var core = dart.import(core);
   function wub() {
     try {
       throw "on without exception parameter";
-    } catch (e$) {
-      if (dart.is(e$, core.String)) {
+    } catch (e) {
+      if (dart.is(e, core.String)) {
       } else
-        throw e$;
+        throw e;
     }
 
   }