Call Dart plugin registrant if available

Author: Emmanuel Garcia

runtime/dart_isolate.cc

@@ -674,6 +674,7 @@ bool DartIsolate::MarkIsolateRunnable() {
 
 [[nodiscard]] static bool InvokeMainEntrypoint(
     Dart_Handle user_entrypoint_function,
+    Dart_Handle plugin_registrant_function,
     Dart_Handle args) {
   if (tonic::LogIfError(user_entrypoint_function)) {
     FML_LOG(ERROR) << "Could not resolve main entrypoint function.";
@@ -689,6 +690,20 @@ bool DartIsolate::MarkIsolateRunnable() {
     return false;
   }
 
+  if (tonic::GetErrorHandleType(plugin_registrant_function) ==
+      tonic::DartErrorHandleType::kNoError) {
+    // The plugin registrant may or may not be defined.
+    // If it's not defined, then continue as usual.
+    // The tests in the framework will ensure that the Dart plugin registrant is
+    // called when defined.
+    if (tonic::LogIfError(tonic::DartInvokeField(
+            Dart_LookupLibrary(tonic::ToDart("dart:ui")), "_runMainZoned",
+            {start_main_isolate_function, plugin_registrant_function, args}))) {
+      FML_LOG(ERROR) << "Could not invoke the Dart plugin registrant.";
+      return false;
+    }
+  }
+
   if (tonic::LogIfError(tonic::DartInvokeField(
           Dart_LookupLibrary(tonic::ToDart("dart:ui")), "_runMainZoned",
           {start_main_isolate_function, user_entrypoint_function, args}))) {
@@ -716,12 +731,18 @@ bool DartIsolate::RunFromLibrary(std::optional<std::string> library_name,
   auto entrypoint_handle = entrypoint.has_value() && !entrypoint.value().empty()
                                ? tonic::ToDart(entrypoint.value().c_str())
                                : tonic::ToDart("main");
+  auto entrypoint_args = tonic::ToDart(args);
   auto user_entrypoint_function =
       ::Dart_GetField(library_handle, entrypoint_handle);
-
-  auto entrypoint_args = tonic::ToDart(args);
-
-  if (!InvokeMainEntrypoint(user_entrypoint_function, entrypoint_args)) {
+  // The Dart plugin registrant is generated by the Flutter tool.
+  // In general, this function binds a plugin implementation to their platform
+  // interface based on the configuration in the app's pubpec.yaml, and the
+  // plugin's pubspec.yaml.
+  auto plugin_registrant_function =
+      ::Dart_GetField(library_handle, tonic::ToDart("_registerPlugins"));
+
+  if (!InvokeMainEntrypoint(user_entrypoint_function,
+                            plugin_registrant_function, entrypoint_args)) {
     return false;
   }