Issue 4919 - Make getBackupFiles in lib/filterStorage.js asynchronous

lib/filterStorage.js

Index: lib/filterStorage.js
===================================================================
--- a/lib/filterStorage.js
+++ b/lib/filterStorage.js
@@ -700,36 +700,58 @@ let FilterStorage = exports.FilterStorag
     );
     if (!explicitFile)
       this._saving = true;
 
     checkBackupRequired(writeFilters, removeLastBackup);
   },
 
   /**
-   * Returns the list of existing backup files.
-   * @return {nsIFile[]}
+   * @typedef FileInfo
+   * @type {object}
+   * @property {nsIFile} file
+   * @property {number} lastModified
+   */
+
+  /**
+   * Returns a promise resolving in a list of existing backup files.
+   * @return {Promise.<FileInfo[]>}
    */
   getBackupFiles()
   {
-    let result = [];
+    let backups = [];
 
     let [, part1, part2] = /^(.*)(\.\w+)$/.exec(
       FilterStorage.sourceFile.leafName
     ) || [null, FilterStorage.sourceFile.leafName, ""];
-    for (let i = 1; ; i++)
+
+    function checkBackupFile(index)
     {
-      let file = FilterStorage.sourceFile.clone();
-      file.leafName = part1 + "-backup" + i + part2;
-      if (file.exists())
-        result.push(file);
-      else
-        break;
+      return new Promise((resolve, reject) =>
+      {
+        let file = FilterStorage.sourceFile.clone();
+        file.leafName = part1 + "-backup" + index + part2;
+
+        IO.statFile(file, (error, result) =>
+        {
+          if (!error && result.exists)
+          {
+            backups.push({
+              file,
+              lastModified: result.lastModified
+            });
+            resolve(checkBackupFile(index + 1));

[kzar, 2017/03/29 11:51:33]

The recursion here is slightly hairy but I can't think of a better alternative
either. I considered Promise.all but since we don't know how many files to check
in advance I guess that wouldn't work.

+          }
+          else
+            resolve(backups);
+        });
+      });
     }
-    return result;
+
+    return checkBackupFile(1);
   }
 };
 
 /**
  * Joins subscription's filters to the subscription without any notifications.
  * @param {Subscription} subscription
  *   filter subscription that should be connected to its filters
  */