Support AOT mode for Windows (#18589)

- Adds a way to provide an AOT library to the C API.
- Adds app.so to the information provided by DartProject.
- Fixes the engine to only do static snapshot linking for Windows in
  debug mode, not all modes, so that the provided library is used.

Engine side of https://github.com/flutter/flutter/issues/38477

runtime/BUILD.gn

@@ -89,28 +89,6 @@ source_set("runtime") {
     "//third_party/skia",
   ]
 
-  # On Windows the engine finds the Dart snapshot data through symbols
-  # that are statically linked into the executable. On other platforms this
-  # data is obtained by a dynamic symbol lookup.
-  # The current Windows platform uses static-link instead of dynamic lookups.
-  # Because:
-  #  1. The size of the executable on Windows is not as concerned as on mobile
-  #     platforms.
-  #  2. If it is a dynamic lookup method, you need to modify the properties of
-  #     the memory page after the *.bin is dynamically loaded at runtime and
-  #     mark it as executable. This is feasible (similar to V8 on Windows), but
-  #     this increases the complexity of the implementation(These operations
-  #     involve the use of some system file/memory privilege APIs and there is
-  #     a risk of failure).
-  #  3. In the executable can enjoy the advantages of the windows preload
-  #     mechanism, speed up I/O.
-  if (is_win) {
-    if (flutter_runtime_mode == "profile" ||
-        flutter_runtime_mode == "release") {
-      deps += [ "//flutter/lib/snapshot" ]
-    }
-  }
-
   public_deps = [
     "//third_party/rapidjson",
   ]

runtime/dart_snapshot.cc

@@ -24,7 +24,7 @@ const char* DartSnapshot::kIsolateInstructionsSymbol =
 // data through symbols that are statically linked into the executable.
 // On other platforms this data is obtained by a dynamic symbol lookup.
 #define DART_SNAPSHOT_STATIC_LINK \
-  (OS_WIN || (OS_ANDROID && FLUTTER_JIT_RUNTIME))
+  ((OS_WIN || OS_ANDROID) && FLUTTER_JIT_RUNTIME)
 
 #if !DART_SNAPSHOT_STATIC_LINK
 

shell/platform/windows/client_wrapper/dart_project_unittests.cc

@@ -22,6 +22,11 @@ class DartProjectTest : public ::testing::Test {
     return project.assets_path();
   }
 
+  // Wrapper for accessing private aot_library_path_.
+  std::wstring GetProjectAotLibraryPath(const DartProject& project) {
+    return project.aot_library_path();
+  }
+
   // Wrapper for accessing private engine_switches.
   std::vector<std::string> GetProjectEngineSwitches(
       const DartProject& project) {
@@ -33,6 +38,7 @@ TEST_F(DartProjectTest, StandardProjectFormat) {
   DartProject project(L"test");
   EXPECT_EQ(GetProjectIcuDataPath(project), L"test\\icudtl.dat");
   EXPECT_EQ(GetProjectAssetsPath(project), L"test\\flutter_assets");
+  EXPECT_EQ(GetProjectAotLibraryPath(project), L"test\\app.so");
 }
 
 TEST_F(DartProjectTest, Switches) {

shell/platform/windows/client_wrapper/flutter_view_controller.cc

@@ -22,6 +22,8 @@ FlutterViewController::FlutterViewController(int width,
   FlutterDesktopEngineProperties properties = {};
   properties.assets_path = project.assets_path().c_str();
   properties.icu_data_path = project.icu_data_path().c_str();
+  // It is harmless to pass this in non-AOT mode.
+  properties.aot_library_path = project.aot_library_path().c_str();
   properties.switches = switch_count > 0 ? switches.data() : nullptr;
   properties.switches_count = switch_count;
   controller_ = FlutterDesktopCreateViewController(width, height, properties);

shell/platform/windows/client_wrapper/include/flutter/dart_project.h

@@ -17,12 +17,14 @@ class DartProject {
   // the following top-level items:
   // - icudtl.dat (provided as a resource by the Flutter tool)
   // - flutter_assets (as built by the Flutter tool)
+  // - app.so, for an AOT build (as built by the Flutter tool)
   //
   // The path can either be absolute, or relative to the directory containing
   // the running executable.
   explicit DartProject(const std::wstring& path) {
     assets_path_ = path + L"\\flutter_assets";
     icu_data_path_ = path + L"\\icudtl.dat";
+    aot_library_path_ = path + L"\\app.so";
   }
 
   ~DartProject() = default;
@@ -48,6 +50,7 @@ class DartProject {
 
   const std::wstring& assets_path() const { return assets_path_; }
   const std::wstring& icu_data_path() const { return icu_data_path_; }
+  const std::wstring& aot_library_path() const { return aot_library_path_; }
   const std::vector<std::string>& engine_switches() const {
     return engine_switches_;
   }
@@ -56,6 +59,9 @@ class DartProject {
   std::wstring assets_path_;
   // The path to the ICU data.
   std::wstring icu_data_path_;
+  // The path to the AOT library. This will always return a path, but non-AOT
+  // builds will not be expected to actually have a library at that path.
+  std::wstring aot_library_path_;
   // Switches to pass to the engine.
   std::vector<std::string> engine_switches_;
 };

shell/platform/windows/flutter_windows.cc

@@ -12,6 +12,7 @@
 #include <cstdlib>
 #include <filesystem>
 #include <iostream>
+#include <memory>
 #include <vector>
 
 #include "flutter/shell/platform/common/cpp/client_wrapper/include/flutter/plugin_registrar.h"
@@ -29,6 +30,33 @@
 
 static_assert(FLUTTER_ENGINE_VERSION == 1, "");
 
+// Attempts to load AOT data from the given path, which must be absolute and
+// non-empty. Logs and returns nullptr on failure.
+UniqueAotDataPtr LoadAotData(std::filesystem::path aot_data_path) {
+  if (aot_data_path.empty()) {
+    std::cerr
+        << "Attempted to load AOT data, but no aot_library_path was provided."
+        << std::endl;
+    return nullptr;
+  }
+  if (!std::filesystem::exists(aot_data_path)) {
+    std::cerr << "Can't load AOT data from " << aot_data_path.u8string()
+              << "; no such file." << std::endl;
+    return nullptr;
+  }
+  std::string path_string = aot_data_path.u8string();
+  FlutterEngineAOTDataSource source = {};
+  source.type = kFlutterEngineAOTDataSourceTypeElfPath;
+  source.elf_path = path_string.c_str();
+  FlutterEngineAOTData data = nullptr;
+  auto result = FlutterEngineCreateAOTData(&source, &data);
+  if (result != kSuccess) {
+    std::cerr << "Failed to load AOT data from: " << path_string << std::endl;
+    return nullptr;
+  }
+  return UniqueAotDataPtr(data);
+}
+
 // Spins up an instance of the Flutter Engine.
 //
 // This function launches the Flutter Engine in a background thread, supplying
@@ -108,7 +136,12 @@ static std::unique_ptr<FlutterDesktopEngineState> RunFlutterEngine(
 
   std::filesystem::path assets_path(engine_properties.assets_path);
   std::filesystem::path icu_path(engine_properties.icu_data_path);
-  if (assets_path.is_relative() || icu_path.is_relative()) {
+  std::filesystem::path aot_library_path =
+      engine_properties.aot_library_path == nullptr
+          ? std::filesystem::path()
+          : std::filesystem::path(engine_properties.aot_library_path);
+  if (assets_path.is_relative() || icu_path.is_relative() ||
+      (!aot_library_path.empty() && aot_library_path.is_relative())) {
     // Treat relative paths as relative to the directory of this executable.
     std::filesystem::path executable_location =
         flutter::GetExecutableDirectory();
@@ -120,10 +153,22 @@ static std::unique_ptr<FlutterDesktopEngineState> RunFlutterEngine(
     }
     assets_path = std::filesystem::path(executable_location) / assets_path;
     icu_path = std::filesystem::path(executable_location) / icu_path;
+    if (!aot_library_path.empty()) {
+      aot_library_path =
+          std::filesystem::path(executable_location) / aot_library_path;
+    }
   }
   std::string assets_path_string = assets_path.u8string();
   std::string icu_path_string = icu_path.u8string();
 
+  if (FlutterEngineRunsAOTCompiledDartCode()) {
+    state->aot_data = LoadAotData(aot_library_path);
+    if (!state->aot_data) {
+      std::cerr << "Unable to start engine without AOT data." << std::endl;
+      return nullptr;
+    }
+  }
+
   FlutterProjectArgs args = {};
   args.struct_size = sizeof(FlutterProjectArgs);
   args.assets_path = assets_path_string.c_str();
@@ -137,6 +182,9 @@ static std::unique_ptr<FlutterDesktopEngineState> RunFlutterEngine(
     return window->HandlePlatformMessage(engine_message);
   };
   args.custom_task_runners = &custom_task_runners;
+  if (state->aot_data) {
+    args.aot_data = state->aot_data.get();
+  }
 
   FLUTTER_API_SYMBOL(FlutterEngine) engine = nullptr;
   auto result =

shell/platform/windows/public/flutter_windows.h

@@ -5,6 +5,7 @@
 #ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_PUBLIC_FLUTTER_H_
 #define FLUTTER_SHELL_PLATFORM_WINDOWS_PUBLIC_FLUTTER_H_
 
+#include <Windows.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -12,8 +13,6 @@
 #include "flutter_messenger.h"
 #include "flutter_plugin_registrar.h"
 
-#include "Windows.h"
-
 #if defined(__cplusplus)
 extern "C" {
 #endif
@@ -40,6 +39,12 @@ typedef struct {
   // containing the executable.
   const wchar_t* icu_data_path;
 
+  // The path to the AOT libary file for your application, if any.
+  // This can either be an absolute path or a path relative to the directory
+  // containing the executable. This can be nullptr for a non-AOT build, as
+  // it will be ignored in that case.
+  const wchar_t* aot_library_path;
+
   // The switches to pass to the Flutter engine.
   //
   // See: https://github.com/flutter/engine/blob/master/shell/common/switches.h

shell/platform/windows/window_state.h

@@ -39,6 +39,14 @@ struct FlutterDesktopView {
   flutter::Win32FlutterWindow* window;
 };
 
+struct AotDataDeleter {
+  void operator()(FlutterEngineAOTData aot_data) {
+    FlutterEngineCollectAOTData(aot_data);
+  }
+};
+
+using UniqueAotDataPtr = std::unique_ptr<_FlutterEngineAOTData, AotDataDeleter>;
+
 // Struct for storing state of a Flutter engine instance.
 struct FlutterDesktopEngineState {
   // The handle to the Flutter engine instance.
@@ -46,6 +54,9 @@ struct FlutterDesktopEngineState {
 
   // Task runner for tasks posted from the engine.
   std::unique_ptr<flutter::Win32TaskRunner> task_runner;
+
+  // AOT data, if any.
+  UniqueAotDataPtr aot_data;
 };
 
 // State associated with the plugin registrar.