Use the standard [[nodiscard]] attribute instead of an FML macro.

assets/asset_resolver.h

@@ -21,8 +21,7 @@ class AssetResolver {
 
   virtual bool IsValid() const = 0;
 
-  FML_WARN_UNUSED_RESULT
-  virtual std::unique_ptr<fml::Mapping> GetAsMapping(
+  [[nodiscard]] virtual std::unique_ptr<fml::Mapping> GetAsMapping(
       const std::string& asset_name) const = 0;
 
  private:

flow/layers/layer.h

@@ -84,7 +84,7 @@ class Layer {
   // destruction.
   class AutoPrerollSaveLayerState {
    public:
-    FML_WARN_UNUSED_RESULT static AutoPrerollSaveLayerState Create(
+    [[nodiscard]] static AutoPrerollSaveLayerState Create(
         PrerollContext* preroll_context,
         bool save_layer_is_active = true,
         bool layer_itself_performs_readback = false);
@@ -133,12 +133,11 @@ class Layer {
   // draws a checkerboard over the layer if that is enabled in the PaintContext.
   class AutoSaveLayer {
    public:
-    FML_WARN_UNUSED_RESULT static AutoSaveLayer Create(
-        const PaintContext& paint_context,
-        const SkRect& bounds,
-        const SkPaint* paint);
+    [[nodiscard]] static AutoSaveLayer Create(const PaintContext& paint_context,
+                                              const SkRect& bounds,
+                                              const SkPaint* paint);
 
-    FML_WARN_UNUSED_RESULT static AutoSaveLayer Create(
+    [[nodiscard]] static AutoSaveLayer Create(
         const PaintContext& paint_context,
         const SkCanvas::SaveLayerRec& layer_rec);
 

flow/scene_update_context.h

@@ -162,9 +162,8 @@ class SceneUpdateContext {
   // CPU wait. Once Vulkan semaphores are available, this method must return
   // void and the implementation must submit surfaces on its own as soon as the
   // specific canvas operations are done.
-  FML_WARN_UNUSED_RESULT
-  std::vector<std::unique_ptr<SurfaceProducerSurface>> ExecutePaintTasks(
-      CompositorContext::ScopedFrame& frame);
+  [[nodiscard]] std::vector<std::unique_ptr<SurfaceProducerSurface>>
+  ExecutePaintTasks(CompositorContext::ScopedFrame& frame);
 
   float ScaleX() const { return metrics_->scale_x * top_scale_x_; }
   float ScaleY() const { return metrics_->scale_y * top_scale_y_; }

fml/compiler_specific.h

@@ -54,16 +54,6 @@
 #define FML_ALIGNOF(type) __alignof(type)
 #endif
 
-// Annotate a function indicating the caller must examine the return value.
-// Use like:
-//   int foo() FML_WARN_UNUSED_RESULT;
-// To explicitly ignore a result, see |ignore_result()| in base/macros.h.
-#if defined(__GNUC__) || defined(__clang__)
-#define FML_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
-#else
-#define FML_WARN_UNUSED_RESULT
-#endif
-
 // Tell the compiler a function is using a printf-style format string.
 // |format_param| is the one-based index of the format string parameter;
 // |dots_param| is the one-based index of the "..." parameter.

fml/message.h

@@ -87,23 +87,23 @@ class Message {
 
   template <typename T,
             typename = std::enable_if_t<std::is_trivially_copyable<T>::value>>
-  FML_WARN_UNUSED_RESULT bool Encode(const T& value) {
+  [[nodiscard]] bool Encode(const T& value) {
     if (auto* buffer = PrepareEncode(sizeof(T))) {
       ::memcpy(buffer, &value, sizeof(T));
       return true;
     }
     return false;
   }
 
-  FML_WARN_UNUSED_RESULT bool Encode(const MessageSerializable& value) {
+  [[nodiscard]] bool Encode(const MessageSerializable& value) {
     return value.Serialize(*this);
   }
 
   template <typename Traits,
             typename T,
             typename = std::enable_if_t<
                 std::is_base_of<MessageSerializable, T>::value>>
-  FML_WARN_UNUSED_RESULT bool Encode(const std::unique_ptr<T>& value) {
+  [[nodiscard]] bool Encode(const std::unique_ptr<T>& value) {
     // Encode if null.
     if (!Encode(static_cast<bool>(value))) {
       return false;
@@ -130,23 +130,23 @@ class Message {
 
   template <typename T,
             typename = std::enable_if_t<std::is_trivially_copyable<T>::value>>
-  FML_WARN_UNUSED_RESULT bool Decode(T& value) {
+  [[nodiscard]] bool Decode(T& value) {
     if (auto* buffer = PrepareDecode(sizeof(T))) {
       ::memcpy(&value, buffer, sizeof(T));
       return true;
     }
     return false;
   }
 
-  FML_WARN_UNUSED_RESULT bool Decode(MessageSerializable& value) {
+  [[nodiscard]] bool Decode(MessageSerializable& value) {
     return value.Deserialize(*this);
   }
 
   template <typename Traits,
             typename T,
             typename = std::enable_if_t<
                 std::is_base_of<MessageSerializable, T>::value>>
-  FML_WARN_UNUSED_RESULT bool Decode(std::unique_ptr<T>& value) {
+  [[nodiscard]] bool Decode(std::unique_ptr<T>& value) {
     // Decode if null.
     bool is_null = false;
     if (!Decode(is_null)) {
@@ -184,17 +184,13 @@ class Message {
   size_t data_length_ = 0;
   size_t size_read_ = 0;
 
-  FML_WARN_UNUSED_RESULT
-  bool Reserve(size_t size);
+  [[nodiscard]] bool Reserve(size_t size);
 
-  FML_WARN_UNUSED_RESULT
-  bool Resize(size_t size);
+  [[nodiscard]] bool Resize(size_t size);
 
-  FML_WARN_UNUSED_RESULT
-  uint8_t* PrepareEncode(size_t size);
+  [[nodiscard]] uint8_t* PrepareEncode(size_t size);
 
-  FML_WARN_UNUSED_RESULT
-  uint8_t* PrepareDecode(size_t size);
+  [[nodiscard]] uint8_t* PrepareDecode(size_t size);
 
   FML_DISALLOW_COPY_AND_ASSIGN(Message);
 };

fml/platform/darwin/scoped_block.h

@@ -72,7 +72,7 @@ class ScopedBlock {
     block_ = temp;
   }
 
-  B release() FML_WARN_UNUSED_RESULT {
+  [[nodiscard]] B release() {
     B temp = block_;
     block_ = nullptr;
     return temp;

fml/platform/darwin/scoped_nsobject.h

@@ -79,7 +79,7 @@ class scoped_nsprotocol {
   // scoped_nsprotocol<>::release() is like scoped_ptr<>::release.  It is NOT a
   // wrapper for [object_ release].  To force a scoped_nsprotocol<> to call
   // [object_ release], use scoped_nsprotocol<>::reset().
-  NST release() FML_WARN_UNUSED_RESULT {
+  [[nodiscard]] NST release() {
     NST temp = object_;
     object_ = nil;
     return temp;

fml/synchronization/semaphore.h

@@ -22,8 +22,7 @@ class Semaphore {
 
   bool IsValid() const;
 
-  FML_WARN_UNUSED_RESULT
-  bool TryWait();
+  [[nodiscard]] bool TryWait();
 
   void Signal();
 

fml/unique_object.h

@@ -78,7 +78,7 @@ class UniqueObject {
   // Release the object. The return value is the current object held by this
   // object. After this operation, this object will hold an invalid value, and
   // will not own the object any more.
-  T release() FML_WARN_UNUSED_RESULT {
+  [[nodiscard]] T release() {
     T old_generic = data_.generic;
     data_.generic = Traits::InvalidValue();
     return old_generic;

runtime/dart_isolate.cc

@@ -338,8 +338,7 @@ bool DartIsolate::LoadKernel(std::shared_ptr<const fml::Mapping> mapping,
   return true;
 }
 
-FML_WARN_UNUSED_RESULT
-bool DartIsolate::PrepareForRunningFromKernel(
+[[nodiscard]] bool DartIsolate::PrepareForRunningFromKernel(
     std::shared_ptr<const fml::Mapping> mapping,
     bool last_piece) {
   TRACE_EVENT0("flutter", "DartIsolate::PrepareForRunningFromKernel");
@@ -405,8 +404,7 @@ bool DartIsolate::PrepareForRunningFromKernel(
   return true;
 }
 
-FML_WARN_UNUSED_RESULT
-bool DartIsolate::PrepareForRunningFromKernels(
+[[nodiscard]] bool DartIsolate::PrepareForRunningFromKernels(
     std::vector<std::shared_ptr<const fml::Mapping>> kernels) {
   const auto count = kernels.size();
   if (count == 0) {
@@ -423,8 +421,7 @@ bool DartIsolate::PrepareForRunningFromKernels(
   return true;
 }
 
-FML_WARN_UNUSED_RESULT
-bool DartIsolate::PrepareForRunningFromKernels(
+[[nodiscard]] bool DartIsolate::PrepareForRunningFromKernels(
     std::vector<std::unique_ptr<const fml::Mapping>> kernels) {
   std::vector<std::shared_ptr<const fml::Mapping>> shared_kernels;
   for (auto& kernel : kernels) {
@@ -460,9 +457,9 @@ bool DartIsolate::MarkIsolateRunnable() {
   return true;
 }
 
-FML_WARN_UNUSED_RESULT
-static bool InvokeMainEntrypoint(Dart_Handle user_entrypoint_function,
-                                 Dart_Handle args) {
+[[nodiscard]] static bool InvokeMainEntrypoint(
+    Dart_Handle user_entrypoint_function,
+    Dart_Handle args) {
   if (tonic::LogIfError(user_entrypoint_function)) {
     FML_LOG(ERROR) << "Could not resolve main entrypoint function.";
     return false;
@@ -488,10 +485,9 @@ static bool InvokeMainEntrypoint(Dart_Handle user_entrypoint_function,
 }
 
 /// @note Procedure doesn't copy all closures.
-FML_WARN_UNUSED_RESULT
-bool DartIsolate::Run(const std::string& entrypoint_name,
-                      const std::vector<std::string>& args,
-                      const fml::closure& on_run) {
+[[nodiscard]] bool DartIsolate::Run(const std::string& entrypoint_name,
+                                    const std::vector<std::string>& args,
+                                    const fml::closure& on_run) {
   TRACE_EVENT0("flutter", "DartIsolate::Run");
   if (phase_ != Phase::Ready) {
     return false;
@@ -517,11 +513,11 @@ bool DartIsolate::Run(const std::string& entrypoint_name,
 }
 
 /// @note Procedure doesn't copy all closures.
-FML_WARN_UNUSED_RESULT
-bool DartIsolate::RunFromLibrary(const std::string& library_name,
-                                 const std::string& entrypoint_name,
-                                 const std::vector<std::string>& args,
-                                 const fml::closure& on_run) {
+[[nodiscard]] bool DartIsolate::RunFromLibrary(
+    const std::string& library_name,
+    const std::string& entrypoint_name,
+    const std::vector<std::string>& args,
+    const fml::closure& on_run) {
   TRACE_EVENT0("flutter", "DartIsolate::RunFromLibrary");
   if (phase_ != Phase::Ready) {
     return false;

runtime/dart_isolate.h

@@ -241,8 +241,7 @@ class DartIsolate : public UIDartState {
   /// @return     Whether the isolate was prepared and the described phase
   ///             transition made.
   ///
-  FML_WARN_UNUSED_RESULT
-  bool PrepareForRunningFromPrecompiledCode();
+  [[nodiscard]] bool PrepareForRunningFromPrecompiledCode();
 
   //----------------------------------------------------------------------------
   /// @brief      Prepare the isolate for running for a a list of kernel files.
@@ -265,9 +264,9 @@ class DartIsolate : public UIDartState {
   /// @return     If the kernel mapping supplied was successfully used to
   ///             prepare the isolate.
   ///
-  FML_WARN_UNUSED_RESULT
-  bool PrepareForRunningFromKernel(std::shared_ptr<const fml::Mapping> kernel,
-                                   bool last_piece = true);
+  [[nodiscard]] bool PrepareForRunningFromKernel(
+      std::shared_ptr<const fml::Mapping> kernel,
+      bool last_piece = true);
 
   //----------------------------------------------------------------------------
   /// @brief      Prepare the isolate for running for a a list of kernel files.
@@ -284,8 +283,7 @@ class DartIsolate : public UIDartState {
   /// @return     If the kernel mappings supplied were successfully used to
   ///             prepare the isolate.
   ///
-  FML_WARN_UNUSED_RESULT
-  bool PrepareForRunningFromKernels(
+  [[nodiscard]] bool PrepareForRunningFromKernels(
       std::vector<std::shared_ptr<const fml::Mapping>> kernels);
 
   //----------------------------------------------------------------------------
@@ -303,8 +301,7 @@ class DartIsolate : public UIDartState {
   /// @return     If the kernel mappings supplied were successfully used to
   ///             prepare the isolate.
   ///
-  FML_WARN_UNUSED_RESULT
-  bool PrepareForRunningFromKernels(
+  [[nodiscard]] bool PrepareForRunningFromKernels(
       std::vector<std::unique_ptr<const fml::Mapping>> kernels);
 
   //----------------------------------------------------------------------------
@@ -323,10 +320,9 @@ class DartIsolate : public UIDartState {
   /// @return     If the isolate successfully transitioned to the running phase
   ///             and the main entrypoint was invoked.
   ///
-  FML_WARN_UNUSED_RESULT
-  bool Run(const std::string& entrypoint,
-           const std::vector<std::string>& args,
-           const fml::closure& on_run = nullptr);
+  [[nodiscard]] bool Run(const std::string& entrypoint,
+                         const std::vector<std::string>& args,
+                         const fml::closure& on_run = nullptr);
 
   //----------------------------------------------------------------------------
   /// @brief      Transition the root isolate to the `Phase::Running` phase and
@@ -346,20 +342,18 @@ class DartIsolate : public UIDartState {
   /// @return     If the isolate successfully transitioned to the running phase
   ///             and the main entrypoint was invoked.
   ///
-  FML_WARN_UNUSED_RESULT
-  bool RunFromLibrary(const std::string& library_name,
-                      const std::string& entrypoint,
-                      const std::vector<std::string>& args,
-                      const fml::closure& on_run = nullptr);
+  [[nodiscard]] bool RunFromLibrary(const std::string& library_name,
+                                    const std::string& entrypoint,
+                                    const std::vector<std::string>& args,
+                                    const fml::closure& on_run = nullptr);
 
   //----------------------------------------------------------------------------
   /// @brief      Transition the isolate to the `Phase::Shutdown` phase. The
   ///             only thing left to do is to collect the isolate.
   ///
   /// @return     If the isolate succesfully transitioned to the shutdown phase.
   ///
-  FML_WARN_UNUSED_RESULT
-  bool Shutdown();
+  [[nodiscard]] bool Shutdown();
 
   //----------------------------------------------------------------------------
   /// @brief      Registers a callback that will be invoked in isolate scope
@@ -418,19 +412,17 @@ class DartIsolate : public UIDartState {
               std::string advisory_script_uri,
               std::string advisory_script_entrypoint,
               bool is_root_isolate);
-  FML_WARN_UNUSED_RESULT bool Initialize(Dart_Isolate isolate);
+  [[nodiscard]] bool Initialize(Dart_Isolate isolate);
 
   void SetMessageHandlingTaskRunner(fml::RefPtr<fml::TaskRunner> runner);
 
   bool LoadKernel(std::shared_ptr<const fml::Mapping> mapping, bool last_piece);
 
-  FML_WARN_UNUSED_RESULT
-  bool LoadLibraries();
+  [[nodiscard]] bool LoadLibraries();
 
   bool UpdateThreadPoolNames() const;
 
-  FML_WARN_UNUSED_RESULT
-  bool MarkIsolateRunnable();
+  [[nodiscard]] bool MarkIsolateRunnable();
 
   void OnShutdownCallback();
 

runtime/dart_service_isolate.h

@@ -33,8 +33,7 @@ class DartServiceIsolate {
 
   // Returns a handle for the callback that can be used in
   // RemoveServerStatusCallback
-  FML_WARN_UNUSED_RESULT
-  static CallbackHandle AddServerStatusCallback(
+  [[nodiscard]] static CallbackHandle AddServerStatusCallback(
       const ObservatoryServerStateCallback& callback);
 
   // Accepts the handle returned by AddServerStatusCallback

runtime/dart_vm_lifecycle.h

@@ -26,10 +26,10 @@ namespace flutter {
 // DartVMRef instances may be created on any thread.
 class DartVMRef {
  public:
-  FML_WARN_UNUSED_RESULT
-  static DartVMRef Create(Settings settings,
-                          fml::RefPtr<DartSnapshot> vm_snapshot = nullptr,
-                          fml::RefPtr<DartSnapshot> isolate_snapshot = nullptr);
+  [[nodiscard]] static DartVMRef Create(
+      Settings settings,
+      fml::RefPtr<DartSnapshot> vm_snapshot = nullptr,
+      fml::RefPtr<DartSnapshot> isolate_snapshot = nullptr);
 
   DartVMRef(DartVMRef&&);
 

runtime/service_protocol.cc

@@ -146,8 +146,7 @@ bool ServiceProtocol::HandleMessage(std::string_view method,
   return service_protocol->HandleMessage(method, params, response);
 }
 
-FML_WARN_UNUSED_RESULT
-static bool HandleMessageOnHandler(
+[[nodiscard]] static bool HandleMessageOnHandler(
     ServiceProtocol::Handler* handler,
     std::string_view method,
     const ServiceProtocol::Handler::ServiceProtocolMap& params,