Check for duplicate library names

lib/src/codegen/js_codegen.dart

Index: lib/src/codegen/js_codegen.dart
diff --git a/lib/src/codegen/js_codegen.dart b/lib/src/codegen/js_codegen.dart
index 87d29fceef6978e42cd9af85c9c150f20aec3050..109462fe52b33b594f725a7f3281a2f41f92d2dd 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -114,7 +114,6 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
         jsDefaultValue = getConstantField(jsName, 'name', types.stringType);
       }
     }
-    if (jsDefaultValue == null) jsDefaultValue = '{}';
 
     // TODO(jmesserly): visit scriptTag, directives?
 
@@ -163,16 +162,16 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     }
 
     var name = new JS.Identifier(jsLibraryName(currentLibrary));

[Jennifer Messerly, 2015/06/05 16:22:27]

suggestion, maybe build the Identifier later, and have `name` store the String?

String name = jsLibraryName(currentLibrary);


That way the string can be used directly, instead of `name.name`

I think in most places, js_ast will implicitly convert the string to an
identifier (for better or worse), but if needed, could do:

var nameId = new JS.Identifier(name);

[vsm, 2015/06/05 17:01:04]

Done.

+    var jsName = js.string(name.name, "'");
 
     // TODO(jmesserly): it would be great to run the renamer on the body,
     // then figure out if we really need each of these parameters.
     // See ES6 modules: https://github.com/dart-lang/dev_compiler/issues/34
     var program = [
-      js.statement('var # = dart.defineLibrary(#, #);', [
-        name,
-        name,
-        js.call(jsDefaultValue)
-      ])
+      jsDefaultValue != null
+          ? js.statement(
+              'dart.defineLibrary(#, #);', [jsName, js.call(jsDefaultValue)])
+          : js.statement('dart.defineLibrary(#);', [jsName])
     ];
 
     var params = [_exportsVar];
@@ -182,7 +181,8 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
       params.add(temp);
       args.add(name);
       var helper = _loader.libraryIsLoaded(library) ? 'import' : 'lazyImport';
-      program.add(js.statement('var # = dart.#(#);', [name, helper, name]));
+      program
+          .add(js.statement('dart.#(#);', [helper, js.string(name.name, "'")]));
     });
 
     program.add(js.statement("(function(#) { 'use strict'; #; })(#);", [