Fixes in codegen and test script

lib/src/codegen/js_codegen.dart

 // Copyright (c) 2015, 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.
 
 library dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet;
 import 'dart:io' show Directory, File;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
@@ skipping 1519 matching lines @@
   }
 
   @override
   JS.Statement visitCatchClause(CatchClause node) {
     var body = [];
 
     var savedCatch = _catchParameter;
     if (node.catchKeyword != null) {
       var name = node.exceptionParameter;
       if (name != null && name.name != _catchParameter) {
-        body.add(js.statement('let # = #;', [_visit(name), _catchParameter]));

[Jennifer Messerly, 2015/03/11 20:28:54]

hmmm. This is not going to have source location associated with the variable.
Maybe not a big deal. (maybe we should put it on the assignment statement
anyway)

Curious, what did this generate as? I'm worried if our visitSimpleIdentifier
logic isn't catching all of these cases.  If it's wrong here it would be wrong
in other cases (right?)... I think it started too simple -- Analyzer's visitors
tend to do more significant series of checks. Probably we should visit the
Element and make sure all of the cases are handled.

(another thing we should probably be using more is inSetterContext)

[Siggi Cherem (dart-lang), 2015/03/11 23:27:22]

Oh, I see.
Here the problem was that visitSimpleIdentifier is assuming that identifiers are
expressions, so it was returning a VariableUse. The let statement expects a
VariableDeclaration or a name, so for example, here is the error you'd get from
js_ast with the regression test (`try_catch.dart`):


Interpolated value #0 is not a VariableDeclaration or String: VariableUse(e)
#0      InstantiatorGeneratorVisitor.error
(package:dev_compiler/src/js/template.dart:154:5)
#1     
InstantiatorGeneratorVisitor.visitInterpolatedVariableDeclaration.<anonymous
closure> (package:dev_compiler/src/js/template.dart:295:19)
#2      InstantiatorGeneratorVisitor.visitVariableInitialization.<anonymous
closure> (package:dev_compiler/src/js/template.dart:584:26)
#3      InstantiatorGeneratorVisitor.visitVariableDeclarationList.<anonymous
closure> (package:dev_compiler/src/js/template.dart:560:34)
#4      InstantiatorGeneratorVisitor.visitExpressionStatement.<anonymous
closure> (package:dev_compiler/src/js/template.dart:361:29)
#5      Template.instantiate (package:dev_compiler/src/js/template.dart:104:26)
#6      JsBuilder.statement (package:dev_compiler/src/js/builder.dart:224:32)
#7      JSCodegenVisitor.visitCatchClause
(package:dev_compiler/src/codegen/js_codegen.dart:1540:30)
#8      CatchClause.accept (package:analyzer/src/generated/ast.dart:4078:57)
#9      JSCodegenVisitor._visit
(package:dev_compiler/src/codegen/js_codegen.dart:1730:29)
#10     JSCodegenVisitor._visitList
(package:dev_compiler/src/codegen/js_codegen.dart:1743:46)
#11     JSCodegenVisitor._visitCatch
(package:dev_compiler/src/codegen/js_codegen.dart:1518:44)
#12     JSCodegenVisitor.visitTryStatement
(package:dev_compiler/src/codegen/js_codegen.dart:1497:53)
...


It seemed strange to change the behavior on visitSimpelIdentifier, so instead I
went ahead and created the node with the sourcespan info here.

[Jennifer Messerly, 2015/03/11 23:48:00]

ouch, yeah, it seems like my Template.visitInterpolatedVariableDeclaration is
not general enough to handle that case :|

I'd probably put the blame here on the JS AST structure not quite being what we
want. But yeah, your new code is fine to do, and it's the same workaround we do
elsewhere.

+        body.add(js.statement('let # = #;', [name.name, _catchParameter]));
         _catchParameter = name.name;
       }
       if (node.stackTraceParameter != null) {
         var stackVar = node.stackTraceParameter.name;
         body.add(js.statement(
             'let # = dart.stackTrace(#);', [stackVar, _visit(name)]));
       }
     }
 
     body.add(_visit(node.body));
@@ skipping 486 matching lines @@
 
     // TODO(jmesserly): in many cases marking the end will be unncessary.
     printer.mark(_location(node.end));
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }