ZLPConstants: Convert to Swift

Soon, we'd like to expose a URL to pass to Linking.openURL to bring
the user to the system-level notification settings for the Zulip
app.

I think I was caught by a red herring when getting such a URL on a
simulator running iOS 16. I was using the URL given by the global
variable UIApplicationOpenNotificationSettingsURLString, new in iOS
15.4 --
  https://developer.apple.com/documentation/uikit/uiapplicationopennotificationsettingsurlstring?language=objc
-- and openURL was bringing me to the home page of the Settings app
instead of the Zulip-specific notification settings.

At first, I thought it was failing because I wasn't using the
Swift-only UIApplication.openNotificationSettingsURLString --
  https://developer.apple.com/documentation/uikit/uiapplication/4013180-opennotificationsettingsurlstrin
-- new in iOS 16.0 to replace that
UIApplicationOpenNotificationSettingsURLString, which in the Swift
doc is marked as deprecated:
  https://developer.apple.com/documentation/uikit/uiapplicationopennotificationsettingsurlstring

But then I did this Swift conversion and tried out the iOS 16+
thing, and it gave the same URL with the same bad result. 🤷
Now my theory is that something is busted with how Linking.openURL
works on the simulator. I tried with my iPhone and it opened to the
notification settings, as expected.

Anyway, might as well keep the work I did to convert this small
file, since Swift is the future. After reading docs and forum
discussions, including RN's official doc
  https://reactnative.dev/docs/0.68/native-modules-ios#exporting-swift
, here's what I did:

- Translate the Objective-C implementation, in ZLPConstants.m, to
  Swift, and rename the file from .m to .swift. Make sure it still
  has a PBXFileReference that appears in the ZulipMobile PBXGroup
  and in the "Compile Sources" build phase of the ZulipMobile
  target.
- Remove the .h file, its PBXFileReference, and the one place its
  PBXFileReference appeared: as a member of the ZulipMobile
  PBXGroup.
- Add a ZLPConstantsBridge.m, to register the Swift implementation
  with React Native. Make sure this new file has a PBXFileReference
  that appears in the ZulipMobile PBXGroup and in "Compile Sources".
- We already have a "bridging header",
  ios/ZulipMobile-Bridging-Header.h. Possibly we only need its first
  line, but I'm not sure, and it seems to work as-is.

Author: chrisbobbe

ios/ZulipMobile.xcodeproj/project.pbxproj

@@ -12,8 +12,9 @@
 		13B07FC11A68108700A75B9A /* main.m in Sources */ = {isa = PBXBuildFile; fileRef = 13B07FB71A68108700A75B9A /* main.m */; };
 		42689E9C23466FF7007540AA /* webview in Resources */ = {isa = PBXBuildFile; fileRef = 42689E9B23466FF7007540AA /* webview */; };
 		8B40B9F327F7AEEC00D33897 /* zulip-icons.ttf in Resources */ = {isa = PBXBuildFile; fileRef = 3787526927F5503200B81DB8 /* zulip-icons.ttf */; };
+		8B44AB3E295B7601003D41A8 /* ZLPConstants.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8B44AB3A295B7263003D41A8 /* ZLPConstants.swift */; };
+		8B44AB40295B7D4D003D41A8 /* ZLPConstantsBridge.m in Sources */ = {isa = PBXBuildFile; fileRef = 8B44AB3F295B7D45003D41A8 /* ZLPConstantsBridge.m */; };
 		8BE55043253A2B6600B0BC8A /* LaunchScreen.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 8BE55041253A2B6600B0BC8A /* LaunchScreen.storyboard */; };
-		8BEA1EF024A6983D00674040 /* ZLPConstants.m in Sources */ = {isa = PBXBuildFile; fileRef = 8BEA1EEE24A6983D00674040 /* ZLPConstants.m */; };
 		A148FEFC1E9D8CB900479280 /* zulip.mp3 in Resources */ = {isa = PBXBuildFile; fileRef = A148FEFB1E9D8CB900479280 /* zulip.mp3 */; };
 		A65C1ECEE03CA6692FC807AA /* ExpoModulesProvider.swift in Sources */ = {isa = PBXBuildFile; fileRef = F2C68E38F2AA306A2C56A4B3 /* ExpoModulesProvider.swift */; };
 		C091D09FD11FDDB8E939257D /* libPods-ZulipMobile.a in Frameworks */ = {isa = PBXBuildFile; fileRef = 74F3CD22CB932FA7EEE0BB66 /* libPods-ZulipMobile.a */; };
@@ -34,9 +35,9 @@
 		42689E9B23466FF7007540AA /* webview */ = {isa = PBXFileReference; lastKnownFileType = folder; path = webview; sourceTree = "<group>"; };
 		66E34CC6219226D10091B852 /* ZulipMobile-Bridging-Header.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "ZulipMobile-Bridging-Header.h"; sourceTree = "<group>"; };
 		74F3CD22CB932FA7EEE0BB66 /* libPods-ZulipMobile.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = "libPods-ZulipMobile.a"; sourceTree = BUILT_PRODUCTS_DIR; };
+		8B44AB3A295B7263003D41A8 /* ZLPConstants.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; name = ZLPConstants.swift; path = ZulipMobile/ZLPConstants.swift; sourceTree = "<group>"; };
+		8B44AB3F295B7D45003D41A8 /* ZLPConstantsBridge.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; name = ZLPConstantsBridge.m; path = ZulipMobile/ZLPConstantsBridge.m; sourceTree = "<group>"; };
 		8BE55042253A2B6600B0BC8A /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.storyboard; name = Base; path = ZulipMobile/Base.lproj/LaunchScreen.storyboard; sourceTree = "<group>"; };
-		8BEA1EEE24A6983D00674040 /* ZLPConstants.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = ZLPConstants.m; path = ZulipMobile/ZLPConstants.m; sourceTree = "<group>"; };
-		8BEA1EEF24A6983D00674040 /* ZLPConstants.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = ZLPConstants.h; path = ZulipMobile/ZLPConstants.h; sourceTree = "<group>"; };
 		A148FEFB1E9D8CB900479280 /* zulip.mp3 */ = {isa = PBXFileReference; lastKnownFileType = audio.mp3; path = zulip.mp3; sourceTree = "<group>"; };
 		CFA67D1F1EC23BCB0070048E /* UtilManager.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = UtilManager.m; path = ZulipMobile/UtilManager.m; sourceTree = "<group>"; };
 		CFA67D211EC23BDD0070048E /* UtilManager.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = UtilManager.h; path = ZulipMobile/UtilManager.h; sourceTree = "<group>"; };
@@ -61,8 +62,8 @@
 		13B07FAE1A68108700A75B9A /* ZulipMobile */ = {
 			isa = PBXGroup;
 			children = (
-				8BEA1EEF24A6983D00674040 /* ZLPConstants.h */,
-				8BEA1EEE24A6983D00674040 /* ZLPConstants.m */,
+				8B44AB3F295B7D45003D41A8 /* ZLPConstantsBridge.m */,
+				8B44AB3A295B7263003D41A8 /* ZLPConstants.swift */,
 				3C4249EC1EF6E16500D245F1 /* ZulipMobile.entitlements */,
 				13B07FAF1A68108700A75B9A /* AppDelegate.h */,
 				13B07FB01A68108700A75B9A /* AppDelegate.mm */,
@@ -367,7 +368,8 @@
 			buildActionMask = 2147483647;
 			files = (
 				CFA67D201EC23BCB0070048E /* UtilManager.m in Sources */,
-				8BEA1EF024A6983D00674040 /* ZLPConstants.m in Sources */,
+				8B44AB3E295B7601003D41A8 /* ZLPConstants.swift in Sources */,
+				8B44AB40295B7D4D003D41A8 /* ZLPConstantsBridge.m in Sources */,
 				13B07FBC1A68108700A75B9A /* AppDelegate.mm in Sources */,
 				13B07FC11A68108700A75B9A /* main.m in Sources */,
 				A65C1ECEE03CA6692FC807AA /* ExpoModulesProvider.swift in Sources */,

ios/ZulipMobile/ZLPConstants.h

@@ -0,0 +1,20 @@
+import Foundation
+
+@objc(ZLPConstants)
+class ZLPConstants: NSObject {
+
+
+  // For why we include this, see
+  //   https://reactnative.dev/docs/0.68/native-modules-ios#exporting-constants
+  @objc
+  static func requiresMainQueueSetup() -> Bool {
+    // Initialization may be done on any thread; we don't need access to
+    // UIKit.
+    return false
+  }
+
+  @objc
+  func constantsToExport() -> [String: Any]! {
+    return ["resourceURL": Bundle.main.resourceURL!.absoluteString]
+  }
+}

ios/ZulipMobile/ZLPConstants.m

@@ -0,0 +1,7 @@
+#import "React/RCTBridgeModule.h"
+
+// Register the ZLPConstants implementation with React Native, needed
+// because ZLPConstants is in Swift:
+//   https://reactnative.dev/docs/0.68/native-modules-ios#exporting-swift
+@interface RCT_EXTERN_MODULE(ZLPConstants, NSObject)
+@end

ios/ZulipMobile/ZLPConstants.swift

@@ -180,10 +180,10 @@ function useMessageListProps(props: OuterProps): Props {
 // URL instead, at least in development.  We'd then just need to adjust
 // the `originWhitelist` we pass to `WebView`.
 //
-// - On iOS: We can't easily hardcode this because it includes UUIDs.
-//   So we bring it over the React Native bridge in ZLPConstants.m.
-//   It's a file URL because the app bundle's `resourceURL` is:
-//     https://developer.apple.com/documentation/foundation/bundle/1414821-resourceurl
+// - On iOS: We can't easily hardcode this because it includes UUIDs. So we
+//   bring it over the React Native bridge from our native module
+//   ZLPConstants. It's a file URL because the app bundle's `resourceURL` is:
+//   https://developer.apple.com/documentation/foundation/bundle/1414821-resourceurl
 //
 // - On Android: Different apps' WebViews see different (virtual) root
 //   directories as `file:///`, and in particular the WebView provides