[fuchsia] Expose view_ref as part of dart:fuchsia initialization (#15958)

fixes https://github.com/flutter/flutter/issues/47178

shell/platform/fuchsia/dart-pkg/fuchsia/lib/fuchsia.dart

@@ -18,8 +18,12 @@ Handle _environment;
 @pragma('vm:entry-point')
 Handle _outgoingServices;
 
+@pragma('vm:entry-point')
+Handle _viewRef;
+
 class MxStartupInfo {
   // TODO: refactor Handle to a Channel
+  // https://github.com/flutter/flutter/issues/49439
   static Handle takeEnvironment() {
     if (_outgoingServices == null && Platform.isFuchsia) {
       throw Exception(
@@ -31,6 +35,7 @@ class MxStartupInfo {
   }
 
   // TODO: refactor Handle to a Channel
+  // https://github.com/flutter/flutter/issues/49439
   static Handle takeOutgoingServices() {
     if (_outgoingServices == null && Platform.isFuchsia) {
       throw Exception(
@@ -40,6 +45,18 @@ class MxStartupInfo {
     _outgoingServices = null;
     return handle;
   }
+
+  // TODO: refactor Handle to a ViewRef
+  // https://github.com/flutter/flutter/issues/49439
+  static Handle takeViewRef() {
+    if (_viewRef == null && Platform.isFuchsia) {
+      throw Exception(
+          'Attempting to call takeViewRef more than once per process');
+    }
+    Handle handle = _viewRef;
+    _viewRef = null;
+    return handle;
+  }
 }
 
 void _setReturnCode(int returnCode) native 'SetReturnCode';

shell/platform/fuchsia/dart-pkg/fuchsia/sdk_ext/fuchsia.cc

@@ -102,7 +102,8 @@ void SetReturnCode(Dart_NativeArguments arguments) {
 }  // namespace
 
 void Initialize(fidl::InterfaceHandle<fuchsia::sys::Environment> environment,
-                zx::channel directory_request) {
+                zx::channel directory_request,
+                std::optional<zx::eventpair> view_ref) {
   zircon::dart::Initialize();
 
   Dart_Handle library = Dart_LookupLibrary(ToDart("dart:fuchsia"));
@@ -128,6 +129,13 @@ void Initialize(fidl::InterfaceHandle<fuchsia::sys::Environment> environment,
         ToDart(zircon::dart::Handle::Create(std::move(directory_request))));
     FML_CHECK(!tonic::LogIfError(result));
   }
+
+  if (view_ref) {
+    result = Dart_SetField(
+        library, ToDart("_viewRef"),
+        ToDart(zircon::dart::Handle::Create((*view_ref).release())));
+    FML_CHECK(!tonic::LogIfError(result));
+  }
 }
 
 }  // namespace dart

shell/platform/fuchsia/dart-pkg/fuchsia/sdk_ext/fuchsia.h

@@ -11,7 +11,8 @@ namespace fuchsia {
 namespace dart {
 
 void Initialize(fidl::InterfaceHandle<fuchsia::sys::Environment> environment,
-                zx::channel directory_request);
+                zx::channel directory_request,
+                std::optional<zx::eventpair> view_ref);
 
 }  // namespace dart
 }  // namespace fuchsia

shell/platform/fuchsia/dart_runner/builtin_libraries.cc

@@ -6,6 +6,7 @@
 
 #include <lib/fdio/namespace.h>
 #include <lib/zx/channel.h>
+#include <optional>
 
 #include "dart-pkg/fuchsia/sdk_ext/fuchsia.h"
 #include "flutter/fml/logging.h"
@@ -103,9 +104,10 @@ void InitBuiltinLibrariesForIsolate(
     zx::channel directory_request,
     bool service_isolate) {
   // dart:fuchsia --------------------------------------------------------------
+  // dart runner doesn't care about scenic view ref.
   if (!service_isolate) {
     fuchsia::dart::Initialize(std::move(environment),
-                              std::move(directory_request));
+                              std::move(directory_request), std::nullopt);
   }
 
   // dart:fuchsia.builtin ------------------------------------------------------

shell/platform/fuchsia/flutter/component.cc

@@ -13,7 +13,6 @@
 #include <lib/async/default.h>
 #include <lib/fdio/directory.h>
 #include <lib/fdio/namespace.h>
-#include <lib/ui/scenic/cpp/view_ref_pair.h>
 #include <lib/ui/scenic/cpp/view_token_pair.h>
 #include <lib/vfs/cpp/composed_service_dir.h>
 #include <lib/vfs/cpp/remote_dir.h>
@@ -616,7 +615,6 @@ void Application::CreateView(
       settings_,                     // settings
       std::move(isolate_snapshot_),  // isolate snapshot
       scenic::ToViewToken(std::move(view_token)),  // view token
-      scenic::ViewRefPair::New(),                  // view ref pair
       std::move(fdio_ns_),                         // FDIO namespace
       std::move(directory_request_)                // outgoing request
       ));

shell/platform/fuchsia/flutter/engine.cc

@@ -7,6 +7,7 @@
 #include "engine.h"
 
 #include <lib/async/cpp/task.h>
+#include <lib/ui/scenic/cpp/view_ref_pair.h>
 #include <zircon/status.h>
 #include <sstream>
 
@@ -55,7 +56,6 @@ Engine::Engine(Delegate& delegate,
                flutter::Settings settings,
                fml::RefPtr<const flutter::DartSnapshot> isolate_snapshot,
                fuchsia::ui::views::ViewToken view_token,
-               scenic::ViewRefPair view_ref_pair,
                UniqueFDIONS fdio_ns,
                fidl::InterfaceRequest<fuchsia::io::Directory> directory_request)
     : delegate_(delegate),
@@ -111,9 +111,14 @@ Engine::Engine(Delegate& delegate,
         });
       };
 
+  auto view_ref_pair = scenic::ViewRefPair::New();
   fuchsia::ui::views::ViewRef view_ref;
   view_ref_pair.view_ref.Clone(&view_ref);
 
+  fuchsia::ui::views::ViewRef dart_view_ref;
+  view_ref_pair.view_ref.Clone(&dart_view_ref);
+  zx::eventpair dart_view_ref_event_pair(std::move(dart_view_ref.reference));
+
   // Setup the callback that will instantiate the platform view.
   flutter::Shell::CreateCallback<flutter::PlatformView>
       on_create_platform_view = fml::MakeCopyable(
@@ -256,9 +261,10 @@ Engine::Engine(Delegate& delegate,
     svc->Connect(environment.NewRequest());
 
     isolate_configurator_ = std::make_unique<IsolateConfigurator>(
-        std::move(fdio_ns),              //
-        std::move(environment),          //
-        directory_request.TakeChannel()  //
+        std::move(fdio_ns),                  //
+        std::move(environment),              //
+        directory_request.TakeChannel(),     //
+        std::move(dart_view_ref_event_pair)  //
     );
   }
 

shell/platform/fuchsia/flutter/engine.h

@@ -11,7 +11,6 @@
 #include <fuchsia/ui/views/cpp/fidl.h>
 #include <lib/async-loop/cpp/loop.h>
 #include <lib/sys/cpp/service_directory.h>
-#include <lib/ui/scenic/cpp/view_ref_pair.h>
 #include <lib/zx/event.h>
 
 #include "flutter/fml/macros.h"
@@ -37,7 +36,6 @@ class Engine final {
          flutter::Settings settings,
          fml::RefPtr<const flutter::DartSnapshot> isolate_snapshot,
          fuchsia::ui::views::ViewToken view_token,
-         scenic::ViewRefPair view_ref_pair,
          UniqueFDIONS fdio_ns,
          fidl::InterfaceRequest<fuchsia::io::Directory> directory_request);
   ~Engine();

shell/platform/fuchsia/flutter/isolate_configurator.cc

@@ -16,10 +16,12 @@ namespace flutter_runner {
 IsolateConfigurator::IsolateConfigurator(
     UniqueFDIONS fdio_ns,
     fidl::InterfaceHandle<fuchsia::sys::Environment> environment,
-    zx::channel directory_request)
+    zx::channel directory_request,
+    zx::eventpair view_ref)
     : fdio_ns_(std::move(fdio_ns)),
       environment_(std::move(environment)),
-      directory_request_(std::move(directory_request)) {}
+      directory_request_(std::move(directory_request)),
+      view_ref_(std::move(view_ref)) {}
 
 IsolateConfigurator::~IsolateConfigurator() = default;
 
@@ -42,7 +44,8 @@ bool IsolateConfigurator::ConfigureCurrentIsolate() {
 
 void IsolateConfigurator::BindFuchsia() {
   fuchsia::dart::Initialize(std::move(environment_),
-                            std::move(directory_request_));
+                            std::move(directory_request_),
+                            std::move(view_ref_));
 }
 
 void IsolateConfigurator::BindZircon() {

shell/platform/fuchsia/flutter/isolate_configurator.h

@@ -21,7 +21,8 @@ class IsolateConfigurator final {
   IsolateConfigurator(
       UniqueFDIONS fdio_ns,
       fidl::InterfaceHandle<fuchsia::sys::Environment> environment,
-      zx::channel directory_request);
+      zx::channel directory_request,
+      zx::eventpair view_ref);
 
   ~IsolateConfigurator();
 
@@ -34,6 +35,7 @@ class IsolateConfigurator final {
   UniqueFDIONS fdio_ns_;
   fidl::InterfaceHandle<fuchsia::sys::Environment> environment_;
   zx::channel directory_request_;
+  zx::eventpair view_ref_;
 
   void BindFuchsia();
 

shell/platform/fuchsia/flutter/session_connection.cc

@@ -36,10 +36,6 @@ SessionConnection::SessionConnection(
 
   session_wrapper_.SetDebugName(debug_label_);
 
-  // TODO(SCN-975): Re-enable.
-  //   view_->GetToken(std::bind(&PlatformView::ConnectSemanticsProvider, this,
-  //                             std::placeholders::_1));
-
   root_view_.AddChild(root_node_);
   root_node_.SetEventMask(fuchsia::ui::gfx::kMetricsEventMask |
                           fuchsia::ui::gfx::kSizeChangeHintEventMask);