fix(dart_libs): add _dart suffix only for reserved lib names.

Closes #871

tools/transpiler/src/outputgeneration/DartParseTreeWriter.js

@@ -516,7 +516,19 @@ export class DartParseTreeWriter extends JavaScriptParseTreeWriter {
   }
 
   toString() {
-    return "library " + this.libName + "_dart;\n" + super.toString();
+    return "library " + this._transformLibName(this.libName) + ";\n" + super.toString();
+  }
+
+  _transformLibName(libName) {
+    var parts = libName.split('.');
+    for (var part of parts) {
+      if (DART_RESERVED_WORDS.indexOf(part) != -1) {
+        return libName + '_dart';
+      }
+    }
+    return libName;
   }
 }
 
+// see: https://www.dartlang.org/docs/dart-up-and-running/ch02.html for a full list.
+const DART_RESERVED_WORDS = ['if', 'switch'];

tools/transpiler/unittest/transpilertests.js

@@ -27,7 +27,7 @@ describe('transpile to dart', function(){
         "var s1:string = \"${a}\";" +
         "var s2:string = '\\${a}';" +
         "var s3:string = '$a';");
-      expect(result.js).toBe("library test_dart;\n" +
+      expect(result.js).toBe("library test;\n" +
       "num a = 1;\n" +
       "String s1 = \"\\${a}\";\n" +
       "String s2 = '\\${a}';\n" +
@@ -39,7 +39,7 @@ describe('transpile to dart', function(){
         "var a:number = 1;" +
         "var s1:string = `$a`;" +
         "var s2:string = `\\$a`;");
-      expect(result.js).toBe("library test_dart;\n" +
+      expect(result.js).toBe("library test;\n" +
       "num a = 1;\n" +
       "String s1 = '''\\$a''';\n" +
       "String s2 = '''\\$a''';\n");
@@ -49,7 +49,7 @@ describe('transpile to dart', function(){
       var result = compiler.compile(options, "test.js",
         "var a:number = 1;" +
         "var s1:string = `${a}`;");
-      expect(result.js).toBe("library test_dart;\n" +
+      expect(result.js).toBe("library test;\n" +
       "num a = 1;\n" +
       "String s1 = '''${a}''';\n");
     });
@@ -60,25 +60,31 @@ describe('transpile to dart', function(){
     it('should support types without generics', function() {
       var result = compiler.compile(options, "test.js",
         "var a:List = [];");
-      expect(result.js).toBe("library test_dart;\nList a = [];\n");
+      expect(result.js).toBe("library test;\nList a = [];\n");
     });
 
     it('should support one level generics', function() {
       var result = compiler.compile(options, "test.js",
         "var a:List<string> = [];");
-      expect(result.js).toBe("library test_dart;\nList<String> a = [];\n");
+      expect(result.js).toBe("library test;\nList<String> a = [];\n");
     });
 
     it('should support multiple one level generics', function() {
       var result = compiler.compile(options, "test.js",
         "var a:List<A,B> = [];");
-      expect(result.js).toBe("library test_dart;\nList<A, B> a = [];\n");
+      expect(result.js).toBe("library test;\nList<A, B> a = [];\n");
     });
 
     it('should support nested generics', function() {
       var result = compiler.compile(options, "test.js",
         "var a:List<A<B>> = [];");
-      expect(result.js).toBe("library test_dart;\nList<A<B>> a = [];\n");
+      expect(result.js).toBe("library test;\nList<A<B>> a = [];\n");
+    });
+
+    it('should add dart suffix to reserved words', function() {
+      var result = compiler.compile(options, "project/if.js",
+        "var a;");
+      expect(result.js).toBe("library project.if_dart;\nvar a;\n");
     });
   });
 });