fix #626, add AMD module format and make it default

lib/src/compiler/module_builder.dart

Index: lib/src/compiler/module_builder.dart
diff --git a/lib/src/compiler/module_builder.dart b/lib/src/compiler/module_builder.dart
index 6e72217f6d65df982eb17ce7384ef565e94f6e54..ef607040c83a449db2ad5a43605e953de0150658 100644
--- a/lib/src/compiler/module_builder.dart
+++ b/lib/src/compiler/module_builder.dart
@@ -105,8 +105,8 @@ class LegacyModuleBuilder extends _ModuleBuilder {
   }
 }
 
-/// Generates node modules.
-class NodeModuleBuilder extends _ModuleBuilder {
+/// Generates commonjs modules (used by node.js).

[nweiz, 2016/08/16 22:14:54]

Nit: "CommonJS" and "Node.js"

[Jennifer Messerly, 2016/08/24 22:39:51]

Done.

+class CommonJSModuleBuilder extends _ModuleBuilder {
   Program build(Program module) {
     var importStatements = <Statement>[];
 
@@ -152,6 +152,54 @@ class NodeModuleBuilder extends _ModuleBuilder {
   }
 }
 
+/// Generates requirejs/AMD modules (popular for use in browser).
+class RequireJSModuleBuilder extends _ModuleBuilder {
+  Program build(Program module) {
+    var importStatements = <Statement>[];
+
+    // Collect imports/exports/statements.
+    visitProgram(module);
+
+    var dependencies = <LiteralString>[];
+    var fnParams = <Parameter>[];
+    for (var import in imports) {
+      // TODO(jmesserly): we could use destructuring once Atom supports it.

[vsm, 2016/08/16 21:23:23]

nit: atom / electron would use common, not requirejs.  :-)

[Jennifer Messerly, 2016/08/16 21:29:28]

thanks, I will clarify that comment. It's more "TODO we haven't bothered to use
destructuring anywhere yet because some impls didn't support it"

+      var moduleVar =
+          new TemporaryId(pathToJSIdentifier(import.from.valueWithoutQuotes));
+      fnParams.add(moduleVar);
+      dependencies.add(import.from);
+
+      // TODO(jmesserly): optimize for the common case of a single import.
+      for (var importName in import.namedImports) {
+        assert(!importName.isStar); // import * not supported yet.

[nweiz, 2016/08/16 22:14:54]

Not supported by what?

[Jennifer Messerly, 2016/08/24 22:39:51]

clarified comment. the compiler doesn't emit `import *`, so we don't need to
support it here

+        var asName = importName.asName ?? importName.name;
+        importStatements.add(js.statement(
+            'const # = #.#', [asName, moduleVar, importName.name.name]));
+      }
+    }
+    statements.insertAll(0, importStatements);
+
+    if (exports.isNotEmpty) {
+      var exportedProps = <Property>[];
+      for (var export in exports) {
+        var names = export.exportedNames;
+        assert(names != null); // export * not supported in legacy modules.

[nweiz, 2016/08/16 22:14:54]

This isn't a legacy module, right?

[Jennifer Messerly, 2016/08/24 22:39:51]

clarified comment. The compiler doesn't emit `export *` (because of legacy
modules), so we don't need to support it.

+        for (var name in names) {
+          exportedProps.add(new Property(js.string(name.name), name));
+        }
+      }
+      statements.add(js.comment('Exports:'));
+      statements.add(
+          new Return(new ObjectInitializer(exportedProps, multiline: true)));
+    }
+
+    var block = js.statement("define(#, function(#) { 'use strict'; #; });",
+        [new ArrayInitializer(dependencies), fnParams, statements]);
+
+    return new Program([block]);
+  }
+}
+
 /// Escape [name] to make it into a valid identifier.
 String pathToJSIdentifier(String name) {
   return toJSIdentifier(path.basenameWithoutExtension(name));