[Feature] macOS support

Author: chipweinberger

README.md

@@ -275,3 +275,66 @@ public class MainApplication extends FlutterApplication {
   }
 }
 ```
+
+#### MacOS
+
+Due to limmitations on MacOS (see https://github.com/flutter/flutter/issues/65222), you need to put this code in your `lib/main.dart` file
+
+**lib/main.dart**
+```
+@pragma('vm:entry-point')
+void _flutterIsolateEntryPoint() => FlutterIsolate.macosIsolateInitialize();
+```
+
+**You also need to manually fix plugin registration .**
+
+On iOS, Flutter automatically generates a file `GeneratedPluginRegistrant.m` during build that registers all native code plugins during app start. This allows Flutter to find the platform channels.
+
+The generated file looks something like this:
+
+**GeneratedPluginRegistrant.m**
+```
+//
+//  Generated file. Do not edit.
+//
+
+// clang-format off
+
+#import "GeneratedPluginRegistrant.h"
+
+#if __has_include(<flutter_downloader/FlutterDownloaderPlugin.h>)
+#import <flutter_downloader/FlutterDownloaderPlugin.h>
+#else
+@import flutter_downloader;
+#endif
+
+#if __has_include(<path_provider_foundation/PathProviderPlugin.h>)
+#import <path_provider_foundation/PathProviderPlugin.h>
+#else
+@import path_provider_foundation;
+#endif
+
+@implementation GeneratedPluginRegistrant
+
++ (void)registerWithRegistry:(NSObject<FlutterPluginRegistry>*)registry {
+  [FlutterDownloaderPlugin registerWithRegistrar:[registry registrarForPlugin:@"FlutterDownloaderPlugin"]];
+  [PathProviderPlugin registerWithRegistrar:[registry registrarForPlugin:@"PathProviderPlugin"]];
+}
+
+@end
+```
+
+On iOS, this generated file uses Objective-C so `flutter_isolate` can find it using `NSClassFromString(@"GeneratedPluginRegistrant")`.
+
+However, on macOS, this generated file uses Swift & does not use a class, so `NSClassFromString` will not work.
+
+In order to fix plugin registration on MacOS, you need to follow these steps.
+
+1. copy `ios/runner/GeneratedPluginRegistrant.m` from iOS and copy it to `macos/runner/GeneratedPluginRegistrant.m`
+2. copy `ios/runner/GeneratedPluginRegistrant.h` from iOS and copy it to `macos/runner/GeneratedPluginRegistrant.h`
+3. open Xcode, right click on "Runner" -> "Add Files to Runner" and add macos files from steps 1 & 2
+4. delete plugins from `macos/runner/GeneratedPluginRegistrant.m` if they do not support macos
+
+See the example app for a demonstration of this.
+
+

example/ios/Runner.xcodeproj/project.pbxproj

@@ -283,7 +283,7 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
-			shellScript = "/bin/sh \"$FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh\" embed_and_thin";
+			shellScript = "/bin/sh \"$FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh\" embed_and_thin\n";
 		};
 		92A1C2A239E39EB33357B1C8 /* [CP] Embed Pods Frameworks */ = {
 			isa = PBXShellScriptBuildPhase;
@@ -315,7 +315,7 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
-			shellScript = "/bin/sh \"$FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh\" build";
+			shellScript = "/bin/sh \"$FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh\" build\n";
 		};
 		9E3AF0DCD678CD20A6F7D6E8 /* [CP] Check Pods Manifest.lock */ = {
 			isa = PBXShellScriptBuildPhase;

example/lib/main.dart

@@ -1,22 +1,28 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:flutter/material.dart';
 import 'package:flutter_isolate/flutter_isolate.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:flutter_downloader/flutter_downloader.dart';
 
+@pragma('vm:entry-point')
+void _flutterIsolateEntryPoint() => FlutterIsolate.macosIsolateInitialize();
+
 @pragma('vm:entry-point')
 void isolate2(String arg) {
   getTemporaryDirectory().then((dir) async {
     print("isolate2 temporary directory: $dir");
 
-    await FlutterDownloader.initialize(debug: true);
-    FlutterDownloader.registerCallback(AppWidget.downloaderCallback);
+    if (Platform.isMacOS == false) {
+      await FlutterDownloader.initialize(debug: true);
+      FlutterDownloader.registerCallback(AppWidget.downloaderCallback);
 
-    var url = 'https://raw.githubusercontent.com/rmawatson/flutter_isolate/master/README.md';
+      var url = 'https://raw.githubusercontent.com/rmawatson/flutter_isolate/master/README.md';
 
-    // ignore: unused_local_variable
-    final taskId = await FlutterDownloader.enqueue(url: url, savedDir: dir.path);
+      // ignore: unused_local_variable
+      final taskId = await FlutterDownloader.enqueue(url: url, savedDir: dir.path);
+    }
   });
   Timer.periodic(Duration(seconds: 1), (timer) => print("Timer Running From Isolate 2"));
 }

example/macos/.gitignore

@@ -0,0 +1,7 @@
+# Flutter-related
+**/Flutter/ephemeral/
+**/Pods/
+
+# Xcode-related
+**/dgph
+**/xcuserdata/

example/macos/Flutter/Flutter-Debug.xcconfig

@@ -0,0 +1,2 @@
+#include? "Pods/Target Support Files/Pods-Runner/Pods-Runner.debug.xcconfig"
+#include "ephemeral/Flutter-Generated.xcconfig"

example/macos/Flutter/Flutter-Release.xcconfig

@@ -0,0 +1,2 @@
+#include? "Pods/Target Support Files/Pods-Runner/Pods-Runner.release.xcconfig"
+#include "ephemeral/Flutter-Generated.xcconfig"

example/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -0,0 +1,14 @@
+//
+//  Generated file. Do not edit.
+//
+
+import FlutterMacOS
+import Foundation
+
+import flutter_isolate
+import path_provider_foundation
+
+func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  FlutterIsolatePluginMacOS.register(with: registry.registrar(forPlugin: "FlutterIsolatePluginMacOS"))
+  PathProviderPlugin.register(with: registry.registrar(forPlugin: "PathProviderPlugin"))
+}

example/macos/Podfile

@@ -0,0 +1,43 @@
+platform :osx, '10.14'
+
+# CocoaPods analytics sends network stats synchronously affecting flutter build latency.
+ENV['COCOAPODS_DISABLE_STATS'] = 'true'
+
+project 'Runner', {
+  'Debug' => :debug,
+  'Profile' => :release,
+  'Release' => :release,
+}
+
+def flutter_root
+  generated_xcode_build_settings_path = File.expand_path(File.join('..', 'Flutter', 'ephemeral', 'Flutter-Generated.xcconfig'), __FILE__)
+  unless File.exist?(generated_xcode_build_settings_path)
+    raise "#{generated_xcode_build_settings_path} must exist. If you're running pod install manually, make sure \"flutter pub get\" is executed first"
+  end
+
+  File.foreach(generated_xcode_build_settings_path) do |line|
+    matches = line.match(/FLUTTER_ROOT\=(.*)/)
+    return matches[1].strip if matches
+  end
+  raise "FLUTTER_ROOT not found in #{generated_xcode_build_settings_path}. Try deleting Flutter-Generated.xcconfig, then run \"flutter pub get\""
+end
+
+require File.expand_path(File.join('packages', 'flutter_tools', 'bin', 'podhelper'), flutter_root)
+
+flutter_macos_podfile_setup
+
+target 'Runner' do
+  use_frameworks!
+  use_modular_headers!
+
+  flutter_install_all_macos_pods File.dirname(File.realpath(__FILE__))
+  target 'RunnerTests' do
+    inherit! :search_paths
+  end
+end
+
+post_install do |installer|
+  installer.pods_project.targets.each do |target|
+    flutter_additional_macos_build_settings(target)
+  end
+end