db [nfc]: Comment on the use of getApplicationDocumentsDirectory

Signed-off-by: Zixuan James Li <[email protected]>

lib/model/store.dart

@@ -778,19 +778,22 @@ class LiveGlobalStore extends GlobalStore {
 
   /// The file path to use for the app database.
   static Future<File> _dbFile() async {
-    // What directory should we use?
-    //   path_provider's getApplicationSupportDirectory:
-    //     on Android, -> Flutter's PathUtils.getFilesDir -> https://developer.android.com/reference/android/content/Context#getFilesDir()
-    //       -> empirically /data/data/com.zulip.flutter/files/
-    //     on iOS, -> "Library/Application Support" via https://developer.apple.com/documentation/foundation/nssearchpathdirectory/nsapplicationsupportdirectory
-    //     on Linux, -> "${XDG_DATA_HOME:-~/.local/share}/com.zulip.flutter/"
-    //     All seem reasonable.
-    //   path_provider's getApplicationDocumentsDirectory:
-    //     on Android, -> Flutter's PathUtils.getDataDirectory -> https://developer.android.com/reference/android/content/Context#getDir(java.lang.String,%20int)
-    //       with https://developer.android.com/reference/android/content/Context#MODE_PRIVATE
-    //     on iOS, "Document directory" via https://developer.apple.com/documentation/foundation/nssearchpathdirectory/nsdocumentdirectory
-    //     on Linux, -> `xdg-user-dir DOCUMENTS` -> e.g. ~/Documents
-    //     That Linux answer is definitely not a fit.  Harder to tell about the rest.
+    // path_provider's getApplicationSupportDirectory:
+    //   on Android, -> Flutter's PathUtils.getFilesDir -> https://developer.android.com/reference/android/content/Context#getFilesDir()
+    //     -> empirically /data/data/com.zulip.flutter/files/
+    //   on iOS, -> "Library/Application Support" via https://developer.apple.com/documentation/foundation/nssearchpathdirectory/nsapplicationsupportdirectory
+    //   on Linux, -> "${XDG_DATA_HOME:-~/.local/share}/com.zulip.flutter/"
+    //
+    // This is reasonable for iOS per Apple's recommendation:
+    // > Use ["Library/Application Support"] to store all app data files except
+    // > those associated with the user’s documents. For example, you might use
+    // > this directory to store app-created data files, configuration files,
+    // > templates, or other fixed or modifiable resources that are managed by
+    // > the app.
+    // See: https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html#//apple_ref/doc/uid/TP40010672-CH2-SW2
+    //
+    // The paths are reasonable for both Android and Linux, compared to the
+    // ones from using path_provider's getApplicationDocumentsDirectory.
     final dir = await getApplicationSupportDirectory();
     return File(p.join(dir.path, 'zulip.db'));
   }