Support for hot source reloading in the Linux glfw sky_shell (#2755)

- [x] Wire up synchronous script reloading in the library tag handler.
- [x] Allow glfw sky_shell to start from dart source as well as bundle.

flutter/tonic/dart_library_loader.cc

@@ -200,19 +200,88 @@ DartLibraryLoader::DartLibraryLoader(DartState* dart_state)
 DartLibraryLoader::~DartLibraryLoader() {
 }
 
+
+static void BlockWaitingForDependencies(
+    DartLibraryLoader* loader,
+    const std::unordered_set<DartDependency*>& dependencies) {
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner =
+      base::MessageLoop::current()->task_runner();
+  base::RunLoop run_loop;
+  task_runner->PostTask(
+      FROM_HERE,
+      base::Bind(
+          &DartLibraryLoader::WaitForDependencies,
+          base::Unretained(loader),
+          dependencies,
+          base::Bind(
+             base::IgnoreResult(&base::SingleThreadTaskRunner::PostTask),
+             task_runner.get(), FROM_HERE,
+             run_loop.QuitClosure())));
+  run_loop.Run();
+}
+
+static void InnerLoadScript(
+    const std::string& script_uri,
+    DartLibraryLoader* library_loader) {
+  // When spawning isolates, Dart expects the script loading to be completed
+  // before returning from the isolate creation callback. The mojo dart
+  // controller also expects the isolate to be finished loading a script
+  // before the isolate creation callback returns.
+
+  // We block here by creating a nested message pump and waiting for the load
+  // to complete.
+
+  DCHECK(base::MessageLoop::current() != nullptr);
+  base::MessageLoop::ScopedNestableTaskAllower allow(
+      base::MessageLoop::current());
+
+  // Initiate the load.
+  DartLibraryLoader& loader = *library_loader;
+  std::unordered_set<DartDependency*> dependencies;
+  {
+    DartDependencyCatcher dependency_catcher(loader);
+    loader.LoadScript(script_uri);
+    // Copy dependencies before dependency_catcher goes out of scope.
+    dependencies = std::unordered_set<DartDependency*>(
+        dependency_catcher.dependencies());
+  }
+
+  // Run inner message loop.
+  BlockWaitingForDependencies(&loader, dependencies);
+
+  // Finalize loading.
+  LogIfError(Dart_FinalizeLoading(true));
+}
+
+
+static void LoadScriptSync(
+    const std::string& script_uri,
+    DartLibraryLoader* library_loader) {
+  CHECK(base::MessageLoop::current() != nullptr);
+  // Thread has a message loop, use it.
+  InnerLoadScript(script_uri, library_loader);
+}
+
+
 Dart_Handle DartLibraryLoader::HandleLibraryTag(Dart_LibraryTag tag,
                                                 Dart_Handle library,
                                                 Dart_Handle url) {
-  DCHECK(Dart_IsLibrary(library));
+  DCHECK(Dart_IsLibrary(library) || Dart_IsNull(library));
   DCHECK(Dart_IsString(url));
-  if (tag == Dart_kCanonicalizeUrl)
+  if (tag == Dart_kCanonicalizeUrl) {
     return DartState::Current()->library_loader().CanonicalizeURL(library, url);
+  }
   if (tag == Dart_kImportTag) {
     return DartState::Current()->library_loader().Import(library, url);
   }
   if (tag == Dart_kSourceTag) {
     return DartState::Current()->library_loader().Source(library, url);
   }
+  if (tag == Dart_kScriptTag) {
+    LoadScriptSync(StdStringFromDart(url),
+                   &DartState::Current()->library_loader());
+    return Dart_Null();
+  }
   DCHECK(false);
   return Dart_NewApiError("Unknown library tag.");
 }

sky/shell/platform/glfw/init_glfw.cc

@@ -17,11 +17,27 @@
 namespace sky {
 namespace shell {
 
+static bool IsDartFile(const std::string& script_uri) {
+  std::string dart_extension = ".dart";
+  return script_uri.rfind(dart_extension) ==
+         (script_uri.size() - dart_extension.size());
+}
+
 bool InitInteractive() {
   base::CommandLine& command_line = *base::CommandLine::ForCurrentProcess();
 
+  auto args = command_line.GetArgs();
+  if (args.empty())
+    return false;
+
   std::string bundle_path =
       command_line.GetSwitchValueASCII(sky::shell::switches::kFLX);
+
+  if (bundle_path.empty()) {
+    // Alternatively, use the first positional argument.
+    bundle_path = args[0];
+  }
+
   if (bundle_path.empty())
     return false;
 
@@ -38,10 +54,16 @@ bool InitInteractive() {
   CHECK(gfx::GLSurface::InitializeOneOff());
   glfwMakeContextCurrent(NULL);
 
-  std::string script_uri = std::string("file://") + bundle_path;
-  // TODO(abarth): Listen for a GLFW callback to delete this window.
-  (new WindowImpl(window))->RunFromBundle(script_uri, bundle_path);
-
+  if (IsDartFile(bundle_path)) {
+    // Load directly from source.
+    // TODO(abarth): Listen for a GLFW callback to delete this window.
+    (new WindowImpl(window))->RunFromFile(bundle_path);
+  } else {
+    std::string script_uri = std::string("file://") + bundle_path;
+    // Load from a bundle.
+    // TODO(abarth): Listen for a GLFW callback to delete this window.
+    (new WindowImpl(window))->RunFromBundle(script_uri, bundle_path);
+  }
   return true;
 }
 

sky/shell/platform/glfw/window_impl.cc

@@ -99,6 +99,12 @@ void WindowImpl::RunFromBundle(const std::string& script_uri,
   engine_->RunFromBundle(script_uri, bundle_path);
 }
 
+void WindowImpl::RunFromFile(const std::string& file) {
+  // TODO(johnmccutchan): Wire up support for asset bundles when running
+  // from source.
+  engine_->RunFromFile(file, "", "");
+}
+
 void WindowImpl::UpdateViewportMetrics(int width, int height) {
   auto metrics = sky::ViewportMetrics::New();
   metrics->physical_width = width;

sky/shell/platform/glfw/window_impl.h

@@ -26,6 +26,8 @@ class WindowImpl : public mojo::ServiceProvider,
   void RunFromBundle(const std::string& script_uri,
                      const std::string& bundle_path);
 
+  void RunFromFile(const std::string& file);
+
   void UpdateViewportMetrics(int width, int height);
   void DispatchMouseButtonEvent(int button, int action, int mods);
   void DispatchMouseMoveEvent(double x, double y);