Windows: linker compatibility with AppContainer for winuwp target (flutter/engine#24318)

* Update Windows linker settings to be compatible with AppContainer when target==winuwp

engine/src/flutter/shell/platform/embedder/BUILD.gn

@@ -245,6 +245,9 @@ if (enable_unittests) {
     sources = [ "tests/embedder_unittests_proctable.cc" ]
 
     defines = [ "FLUTTER_ENGINE_NO_PROTOTYPES" ]
+    if (is_win) {
+      libs = [ "psapi.lib" ]
+    }
 
     deps = [
       ":embedder",

engine/src/flutter/shell/platform/windows/BUILD.gn

@@ -170,7 +170,10 @@ executable("flutter_windows_unittests") {
   testonly = true
 
   if (target_os == "winuwp") {
-    libs = [ "windowsapp.lib" ]
+    libs = [
+      "windowsapp.lib",
+      "user32.lib",
+    ]
   }
 
   # Common Windows test sources.

engine/src/flutter/shell/platform/windows/key_event_handler.cc

@@ -122,7 +122,12 @@ KeyEventHandler::KeyEventHandler(flutter::BinaryMessenger* messenger,
               kChannelName,
               &flutter::JsonMessageCodec::GetInstance())),
       send_input_(send_input) {
+// As described in the header, UWP doesn't support the SendInput API hence we
+// only need to assert that the delegate is null in the non-UWP case since it is
+// expected to be null in the UWP case.
+#ifndef WINUWP
   assert(send_input != nullptr);
+#endif
 }
 
 KeyEventHandler::~KeyEventHandler() = default;
@@ -190,6 +195,15 @@ void KeyEventHandler::HandleResponse(bool handled,
       std::cerr << "Unable to find event " << id << " in pending events queue.";
       return;
     }
+
+// As described in the header, the user32 SendInput function is not supported in
+// UWP appcontainer and there is no WinRT equivalent hence we pass null for
+// SendInputDelegate param.  Since this handler is one of last resort, it is
+// only applicable for platformview scenarios where the host view can handle
+// input events in the event the Flutter view does not choose to handle them.
+// Since platformview is currently not support for desktop, there is no
+// functional gap caused by this currently.
+#ifndef WINUWP
     INPUT input_event;
     input_event.type = INPUT_KEYBOARD;
     input_event.ki = *key_event;
@@ -199,6 +213,7 @@ void KeyEventHandler::HandleResponse(bool handled,
                    "with scancode "
                 << scancode << " (character " << character << ")" << std::endl;
     }
+#endif
   }
 }
 
@@ -225,6 +240,10 @@ bool KeyEventHandler::KeyboardHook(FlutterWindowsView* view,
   event.AddMember(kKeyMapKey, kWindowsKeyMap, allocator);
 #ifndef WINUWP
   event.AddMember(kModifiersKey, GetModsForKeyState(), allocator);
+#else
+  // TODO: Implement modifiers in UWP codepath
+  // TODO: https://github.com/flutter/flutter/issues/70202
+  event.AddMember(kModifiersKey, 0, allocator);
 #endif
 
   switch (action) {

engine/src/flutter/shell/platform/windows/key_event_handler.h

@@ -27,8 +27,19 @@ class KeyEventHandler : public KeyboardHookHandler {
   using SendInputDelegate =
       std::function<UINT(UINT cInputs, LPINPUT pInputs, int cbSize)>;
 
+// the user32 SendInput function is not supported in UWP appcontainer and there
+// is no WinRT equivalent hence we pass null for SendInputDelegate param.  Since
+// this handler is one of last resort, it is only applicable for platformview
+// scenarios where the host view can handle input events in the event the
+// Flutter view does not choose to handle them. Since platformview is currently
+// not support for desktop, there is no functional gap caused by this currently.
+#ifdef WINUWP
+  explicit KeyEventHandler(flutter::BinaryMessenger* messenger,
+                           SendInputDelegate delegate = nullptr);
+#else
   explicit KeyEventHandler(flutter::BinaryMessenger* messenger,
                            SendInputDelegate delegate = SendInput);
+#endif
 
   virtual ~KeyEventHandler();
 

engine/src/flutter/shell/testing/BUILD.gn

@@ -13,6 +13,14 @@ executable("testing") {
   ]
 
   sources = [ "tester_main.cc" ]
+  if (is_win) {
+    libs = [
+      "psapi.lib",
+      "user32.lib",
+      "FontSub.lib",
+      "shlwapi.lib",
+    ]
+  }
 
   deps = [
     "//flutter/assets",

engine/src/flutter/tools/gn

@@ -105,6 +105,8 @@ def to_gn_args(args):
     gn_args['skia_use_fontconfig'] = args.enable_fontconfig
     gn_args['flutter_use_fontconfig'] = args.enable_fontconfig
     gn_args['flutter_enable_skshaper'] = args.enable_skshaper
+    if args.target_os == 'winuwp':
+      gn_args['skia_enable_winuwp'] = True
     if args.enable_skshaper:
       gn_args['skia_use_icu'] = True
       gn_args['skia_enable_icu_ubrk_safeclone'] = True