Add error logging to GLFW and Flutter setup (#243)

Add error logging when starting the Flutter engine fails (on all
platforms), and on GLFW errors. Also exit early with error logging for
unrecoverable errors in the GLFW implementation.

Fixes #241.

Author: stuartmorgan

example/linux_fde/flutter_embedder_example.cc

@@ -54,7 +54,8 @@ std::string GetExecutableDirectory() {
 
 int main(int argc, char **argv) {
   if (!flutter_desktop_embedding::FlutterInit()) {
-    std::cerr << "Couldn't init GLFW" << std::endl;
+    std::cerr << "Unable to init GLFW; exiting." << std::endl;
+    return EXIT_FAILURE;
   }
 
   // Resources are located relative to the executable.
@@ -76,6 +77,7 @@ int main(int argc, char **argv) {
       640, 480, assets_path, icu_data_path, arguments);
   if (window == nullptr) {
     flutter_desktop_embedding::FlutterTerminate();
+    std::cerr << "Unable to create Flutter window; exiting." << std::endl;
     return EXIT_FAILURE;
   }
 

example/windows_fde/flutter_embedder_example.cpp

@@ -19,7 +19,8 @@
 
 int main(int argc, char **argv) {
   if (!flutter_desktop_embedding::FlutterInit()) {
-    std::cout << "Couldn't init GLFW" << std::endl;
+    std::cerr << "Unable to init GLFW; exiting." << std::endl;
+    return EXIT_FAILURE;
   }
   // Arguments for the Flutter Engine.
   std::vector<std::string> arguments;
@@ -33,6 +34,7 @@ int main(int argc, char **argv) {
       "..\\..\\library\\windows\\dependencies\\engine\\icudtl.dat", arguments);
   if (window == nullptr) {
     flutter_desktop_embedding::FlutterTerminate();
+    std::cerr << "Unable to create Flutter window; exiting." << std::endl;
     return EXIT_FAILURE;
   }
 

library/common/glfw/embedder.cc

@@ -239,6 +239,10 @@ static void *GLFWProcResolver(void *user_data, const char *name) {
   return reinterpret_cast<void *>(glfwGetProcAddress(name));
 }
 
+static void GLFWErrorCallback(int error_code, const char *description) {
+  std::cerr << "GLFW error " << error_code << ": " << description << std::endl;
+}
+
 // Spins up an instance of the Flutter Engine.
 //
 // This function launches the Flutter Engine in a background thread, supplying
@@ -276,17 +280,21 @@ static FlutterEngine RunFlutterEngine(
   auto result =
       FlutterEngineRun(FLUTTER_ENGINE_VERSION, &config, &args, window, &engine);
   if (result != kSuccess || engine == nullptr) {
+    std::cerr << "Failed to start Flutter engine: error " << result
+              << std::endl;
     return nullptr;
   }
   return engine;
 }
 
 namespace flutter_desktop_embedding {
 
-// Initialize glfw
-bool FlutterInit() { return glfwInit(); }
+bool FlutterInit() {
+  // Before making any GLFW calls, set up a logging error handler.
+  glfwSetErrorCallback(GLFWErrorCallback);
+  return glfwInit();
+}
 
-// Tear down glfw
 void FlutterTerminate() { glfwTerminate(); }
 
 PluginRegistrar *GetRegistrarForPlugin(GLFWwindow *flutter_window,

library/macos/FLEViewController.m

@@ -297,10 +297,14 @@ - (BOOL)launchEngineInternalWithAssetsPath:(NSURL *)assets
   flutterArguments.command_line_argv = argv;
   flutterArguments.platform_message_callback = (FlutterPlatformMessageCallback)OnPlatformMessage;
 
-  BOOL result = FlutterEngineRun(FLUTTER_ENGINE_VERSION, &config, &flutterArguments,
-                                 (__bridge void *)(self), &_engine) == kSuccess;
+  FlutterResult result = FlutterEngineRun(FLUTTER_ENGINE_VERSION, &config, &flutterArguments,
+                                 (__bridge void *)(self), &_engine);
   free(argv);
-  return result;
+  if (result != kSuccess) {
+    NSLog(@"Failed to start Flutter engine: error %d", result);
+    return NO;
+  }
+  return YES;
 }
 
 + (FlutterRendererConfig)createRenderConfigHeadless:(BOOL)headless {