Extract invoke-main stub generator.

pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart

+// Copyright (c) 2014, 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.
+
+part of dart2js.js_emitter;
+
+class MainCallStubGenerator {
+  final Compiler compiler;
+  final JavaScriptBackend backend;
+  final CodeEmitterTask emitterTask;
+
+  MainCallStubGenerator(this.compiler, this.backend, this.emitterTask);
+
+  /// Returns the code equivalent to:
+  ///   `function(args) { $.startRootIsolate(X.main$closure(), args); }`
+  jsAst.Expression _buildIsolateSetupClosure(Element appMain,
+                                            Element isolateMain) {
+    jsAst.Expression mainAccess =
+        emitterTask.isolateStaticClosureAccess(appMain);
+    // Since we pass the closurized version of the main method to
+    // the isolate method, we must make sure that it exists.
+    return js('function(a){ #(#, a); }',
+        [emitterTask.staticFunctionAccess(isolateMain), mainAccess]);
+  }
+
+
+  jsAst.Statement generateInvokeMain() {
+    Element main = compiler.mainFunction;
+    jsAst.Expression mainCallClosure = null;
+    if (compiler.hasIsolateSupport) {
+      Element isolateMain =
+        backend.isolateHelperLibrary.find(JavaScriptBackend.START_ROOT_ISOLATE);
+      mainCallClosure = _buildIsolateSetupClosure(main, isolateMain);
+    } else if (compiler.hasIncrementalSupport) {
+      mainCallClosure = js(
+          'function() { return #(); }',
+          emitterTask.staticFunctionAccess(main));
+    } else {
+      mainCallClosure = emitterTask.staticFunctionAccess(main);
+    }
+
+    jsAst.Expression currentScriptAccess =
+        emitterTask.generateEmbeddedGlobalAccess(embeddedNames.CURRENT_SCRIPT);
+
+    // This code finds the currently executing script by listening to the
+    // onload event of all script tags and getting the first script which
+    // finishes. Since onload is called immediately after execution this should
+    // not substantially change execution order.
+    return js.statement('''
+      (function (callback) {
+        if (typeof document === "undefined") {
+          callback(null);
+          return;
+        }
+        if (document.currentScript) {
+          callback(document.currentScript);
+          return;
+        }
+
+        var scripts = document.scripts;
+        function onLoad(event) {
+          for (var i = 0; i < scripts.length; ++i) {
+            scripts[i].removeEventListener("load", onLoad, false);
+          }
+          callback(event.target);
+        }
+        for (var i = 0; i < scripts.length; ++i) {
+          scripts[i].addEventListener("load", onLoad, false);
+        }
+      })(function(currentScript) {
+        #currentScript = currentScript;
+
+        if (typeof dartMainRunner === "function") {
+          dartMainRunner(#mainCallClosure, []);
+        } else {
+          #mainCallClosure([]);
+        }
+      })''',
+      {'currentScript': currentScriptAccess,
+       'mainCallClosure': mainCallClosure});
+  }
+}