feat(share_plus)!: native share dialog for windows

* Platform specific implementation for using DataTransferManager on Windows
* DataTransferManager is only used on (& available for) Windows 10 builds 17763 or higher.
* On older Windows versions, existing old implementation is used i.e. launching mailto: URIs with subject & body query parameters.
* Getting the share result is not supported on Windows. Thus, shareWithResult & shareFilesWithResult always return ShareResultStatus.unavailable.
* This platform specific implementation beings supports for all existing methods available in package:share_plus to Windows, namely: share, shareFiles, shareWithResult, shareFilesWithResult, shareXFiles.

Author: alexmercerind

packages/share_plus/share_plus_windows/.clang-format

@@ -0,0 +1,12 @@
+# Defines the Chromium style for automatic reformatting.
+# http://clang.llvm.org/docs/ClangFormatStyleOptions.html
+BasedOnStyle: Chromium
+# This defaults to 'Auto'. Explicitly set it for a while, so that
+# 'vector<vector<int> >' in existing files gets formatted to
+# 'vector<vector<int>>'. ('Auto' means that clang-format will only use
+# 'int>>' if the file already contains at least one such instance.)
+Standard: Cpp11
+SortIncludes: true
+---
+Language: ObjC
+ColumnLimit: 100

packages/share_plus/share_plus_windows/lib/share_plus_windows.dart

@@ -3,14 +3,19 @@ library share_plus_windows;
 
 import 'dart:ui';
 
+import 'package:share_plus_windows/src/version_helper.dart';
 import 'package:url_launcher/url_launcher.dart';
 import 'package:share_plus_platform_interface/share_plus_platform_interface.dart';
 
-/// The Windows implementation of SharePlatform.
+/// The fallback Windows implementation of [SharePlatform], for older Windows versions.
+///
 class ShareWindows extends SharePlatform {
-  /// Register this dart class as the platform implementation for linux
+  /// If the modern Share UI i.e. `DataTransferManager` is not available, then use this Dart class instead of platform specific implementation.
+  ///
   static void registerWith() {
-    SharePlatform.instance = ShareWindows();
+    if (!VersionHelper.instance.isWindows10RS5OrGreater) {
+      SharePlatform.instance = ShareWindows();
+    }
   }
 
   /// Share text.

packages/share_plus/share_plus_windows/lib/src/version_helper.dart

@@ -0,0 +1,43 @@
+import 'dart:io';
+import 'dart:ffi';
+import 'package:ffi/ffi.dart';
+import 'package:win32/win32.dart';
+
+class VersionHelper {
+  static VersionHelper instance = VersionHelper._();
+
+  /// Whether the current OS is Windows 10 Redstone 5 or later.
+  /// This is used to determine whether the modern Share UI i.e. `DataTransferManager` is available or not.
+  ///
+  /// References: https://en.wikipedia.org/wiki/Windows_10_version_history
+  ///             https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-osversioninfoexa
+  ///
+  bool isWindows10RS5OrGreater = false;
+
+  static const int _kWindows10RS5BuildNumber = 17763;
+
+  VersionHelper._() {
+    if (Platform.isWindows) {
+      final pointer = calloc<OSVERSIONINFOEX>();
+      pointer.ref
+        ..dwOSVersionInfoSize = sizeOf<OSVERSIONINFOEX>()
+        ..dwBuildNumber = 0
+        ..dwMajorVersion = 0
+        ..dwMinorVersion = 0
+        ..dwPlatformId = 0
+        ..szCSDVersion = ''
+        ..wServicePackMajor = 0
+        ..wServicePackMinor = 0
+        ..wSuiteMask = 0
+        ..wProductType = 0
+        ..wReserved = 0;
+      final rtlGetVersion = DynamicLibrary.open('ntdll.dll').lookupFunction<
+          Void Function(Pointer<OSVERSIONINFOEX>),
+          void Function(Pointer<OSVERSIONINFOEX>)>('RtlGetVersion');
+      rtlGetVersion(pointer);
+      isWindows10RS5OrGreater =
+          pointer.ref.dwBuildNumber >= _kWindows10RS5BuildNumber;
+      calloc.free(pointer);
+    }
+  }
+}

packages/share_plus/share_plus_windows/pubspec.yaml

@@ -14,6 +14,8 @@ dependencies:
     sdk: flutter
   meta: ^1.7.0
   url_launcher: ^6.1.2
+  ffi: ^2.0.1
+  win32: ^2.3.8
 
 dev_dependencies:
   flutter_test:
@@ -23,8 +25,6 @@ dev_dependencies:
 
 flutter:
   plugin:
-    implements: share_plus
     platforms:
       windows:
-        dartPluginClass: ShareWindows
-        pluginClass: none
+        pluginClass: SharePlusWindowsPluginCApi

packages/share_plus/share_plus_windows/windows/.gitignore

@@ -0,0 +1,17 @@
+flutter/
+
+# Visual Studio user-specific files.
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+# Visual Studio build-related files.
+x64/
+x86/
+
+# Visual Studio cache files
+# files ending in .cache can be ignored
+*.[Cc]ache
+# but keep track of directories ending in .cache
+!*.[Cc]ache/

packages/share_plus/share_plus_windows/windows/CMakeLists.txt

@@ -0,0 +1,53 @@
+# The Flutter tooling requires that developers have a version of Visual Studio
+# installed that includes CMake 3.14 or later. You should not increase this
+# version, as doing so will cause the plugin to fail to compile for some
+# customers of the plugin.
+cmake_minimum_required(VERSION 3.14)
+
+# Project-level configuration.
+set(PROJECT_NAME "share_plus_windows")
+project(${PROJECT_NAME} LANGUAGES CXX)
+
+# This value is used when generating builds using this plugin, so it must
+# not be changed
+set(PLUGIN_NAME "share_plus_windows_plugin")
+
+# Any new source files that you add to the plugin should be added here.
+list(APPEND PLUGIN_SOURCES
+  "share_plus_windows_plugin.cpp"
+  "share_plus_windows_plugin.h"
+)
+
+# Define the plugin library target. Its name must not be changed (see comment
+# on PLUGIN_NAME above).
+add_library(${PLUGIN_NAME} SHARED
+  "include/share_plus_windows/share_plus_windows_plugin_c_api.h"
+  "share_plus_windows_plugin_c_api.cpp"
+  ${PLUGIN_SOURCES}
+)
+
+# Apply a standard set of build settings that are configured in the
+# application-level CMakeLists.txt. This can be removed for plugins that want
+# full control over build settings.
+apply_standard_settings(${PLUGIN_NAME})
+
+# Symbols are hidden by default to reduce the chance of accidental conflicts
+# between plugins. This should not be removed; any symbols that should be
+# exported should be explicitly exported with the FLUTTER_PLUGIN_EXPORT macro.
+set_target_properties(${PLUGIN_NAME} PROPERTIES
+  CXX_VISIBILITY_PRESET hidden)
+target_compile_definitions(${PLUGIN_NAME} PRIVATE FLUTTER_PLUGIN_IMPL)
+
+# Source include directories and library dependencies. Add any plugin-specific
+# dependencies here.
+target_include_directories(${PLUGIN_NAME} INTERFACE
+  "${CMAKE_CURRENT_SOURCE_DIR}/include")
+target_link_libraries(${PLUGIN_NAME} PRIVATE flutter flutter_wrapper_plugin)
+
+# List of absolute paths to libraries that should be bundled with the plugin.
+# This list could contain prebuilt libraries, or libraries created by an
+# external build triggered from this build file.
+set(share_plus_windows_bundled_libraries
+  ""
+  PARENT_SCOPE
+)

packages/share_plus/share_plus_windows/windows/include/share_plus_windows/share_plus_windows_plugin_c_api.h

@@ -0,0 +1,23 @@
+#ifndef FLUTTER_PLUGIN_SHARE_PLUS_WINDOWS_PLUGIN_C_API_H_
+#define FLUTTER_PLUGIN_SHARE_PLUS_WINDOWS_PLUGIN_C_API_H_
+
+#include <flutter_plugin_registrar.h>
+
+#ifdef FLUTTER_PLUGIN_IMPL
+#define FLUTTER_PLUGIN_EXPORT __declspec(dllexport)
+#else
+#define FLUTTER_PLUGIN_EXPORT __declspec(dllimport)
+#endif
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+FLUTTER_PLUGIN_EXPORT void SharePlusWindowsPluginCApiRegisterWithRegistrar(
+    FlutterDesktopPluginRegistrarRef registrar);
+
+#if defined(__cplusplus)
+}  // extern "C"
+#endif
+
+#endif  // FLUTTER_PLUGIN_SHARE_PLUS_WINDOWS_PLUGIN_C_API_H_