Bug 1657291 - Replace UrlbarPrefsObserver with an ordered list of wea…

…k observers internal to UrlbarPrefs. r=harry

Differential Revision: https://phabricator.services.mozilla.com/D85971

browser/components/urlbar/UrlbarPrefs.jsm

@@ -233,7 +233,16 @@ class Preferences {
    */
   constructor() {
     this._map = new Map();
-    this._observer = new UrlbarPrefsObserver(pref => this._onPrefChanged(pref));
+    this.QueryInterface = ChromeUtils.generateQI([
+      "nsIObserver",
+      "nsISupportsWeakReference",
+    ]);
+    Services.prefs.addObserver(PREF_URLBAR_BRANCH, this, true);
+    for (let pref of PREF_OTHER_DEFAULTS.keys()) {
+      Services.prefs.addObserver(pref, this, true);
+    }
+    this._observerWeakRefs = [];
+    this.addObserver(this);
   }
 
   /**
@@ -271,14 +280,52 @@ class Preferences {
     setter(pref, value);
   }
 
+  /**
+   * Adds a preference observer.  Observers are held weakly.
+   *
+   * @param {object} observer
+   *        An object that must have a method named `onPrefChanged`, which will
+   *        be called when a urlbar preference changes.  It will be passed the
+   *        pref name.  For prefs in the `browser.urlbar.` branch, the name will
+   *        be relative to the branch.  For other prefs, the name will be the
+   *        full name.
+   */
+  addObserver(observer) {
+    this._observerWeakRefs.push(Cu.getWeakReference(observer));
+  }
+
+  /**
+   * Observes preference changes.
+   *
+   * @param {nsISupports} subject
+   * @param {string} topic
+   * @param {string} data
+   */
+  observe(subject, topic, data) {
+    let pref = data.replace(PREF_URLBAR_BRANCH, "");
+    if (!PREF_URLBAR_DEFAULTS.has(pref) && !PREF_OTHER_DEFAULTS.has(pref)) {
+      return;
+    }
+    for (let i = 0; i < this._observerWeakRefs.length; ) {
+      let observer = this._observerWeakRefs[i].get();
+      if (!observer) {
+        // The observer has been GC'ed, so remove it from our list.
+        this._observerWeakRefs.splice(i, 1);
+      } else {
+        observer.onPrefChanged(pref);
+        ++i;
+      }
+    }
+  }
+
   /**
    * Called when a pref tracked by UrlbarPrefs changes.
    *
    * @param {string} pref
    *        The name of the pref, relative to `browser.urlbar.` if the pref is
    *        in that branch.
    */
-  _onPrefChanged(pref) {
+  onPrefChanged(pref) {
     this._map.delete(pref);
     // Some prefs may influence others.
     if (pref == "matchBuckets") {
@@ -403,45 +450,4 @@ class Preferences {
   }
 }
 
-/**
- * A weak preferences observer.  You must hold on to instances of this class
- * because otherwise they will be garbage collected.
- */
-class UrlbarPrefsObserver {
-  /**
-   * Constructor.
-   *
-   * @param {function} callback
-   *   Called when a urlbar preference changes.  It will be passed the pref
-   *   name.  For prefs in the `browser.urlbar.` branch, the name will be
-   *   relative to the branch.  For other prefs, the name will be the full name.
-   */
-  constructor(callback) {
-    this._callback = callback;
-    this.QueryInterface = ChromeUtils.generateQI([
-      "nsIObserver",
-      "nsISupportsWeakReference",
-    ]);
-    Services.prefs.addObserver(PREF_URLBAR_BRANCH, this, true);
-    for (let pref of PREF_OTHER_DEFAULTS.keys()) {
-      Services.prefs.addObserver(pref, this, true);
-    }
-  }
-
-  /**
-   * Observes preference changes.
-   *
-   * @param {nsISupports} subject
-   * @param {string} topic
-   * @param {string} data
-   */
-  observe(subject, topic, data) {
-    let pref = data.replace(PREF_URLBAR_BRANCH, "");
-    if (!PREF_URLBAR_DEFAULTS.has(pref) && !PREF_OTHER_DEFAULTS.has(pref)) {
-      return;
-    }
-    this._callback(pref);
-  }
-}
-
 var UrlbarPrefs = new Preferences();

browser/components/urlbar/UrlbarSearchOneOffs.jsm

@@ -12,7 +12,6 @@ const { XPCOMUtils } = ChromeUtils.import(
 XPCOMUtils.defineLazyModuleGetters(this, {
   SearchOneOffs: "resource:///modules/SearchOneOffs.jsm",
   UrlbarPrefs: "resource:///modules/UrlbarPrefs.jsm",
-  UrlbarPrefsObserver: "resource:///modules/UrlbarPrefs.jsm",
   UrlbarSearchUtils: "resource:///modules/UrlbarSearchUtils.jsm",
   UrlbarTokenizer: "resource:///modules/UrlbarTokenizer.jsm",
   UrlbarUtils: "resource:///modules/UrlbarUtils.jsm",
@@ -57,9 +56,7 @@ class UrlbarSearchOneOffs extends SearchOneOffs {
     super(view.panel.querySelector(".search-one-offs"));
     this.view = view;
     this.input = view.input;
-    this._prefObserver = new UrlbarPrefsObserver(pref =>
-      this._onPrefChanged(pref)
-    );
+    UrlbarPrefs.addObserver(this);
   }
 
   /**
@@ -194,6 +191,23 @@ class UrlbarSearchOneOffs extends SearchOneOffs {
     );
   }
 
+  /**
+   * Called when a pref tracked by UrlbarPrefs changes.
+   *
+   * @param {string} changedPref
+   *   The name of the pref, relative to `browser.urlbar.` if the pref is in
+   *   that branch.
+   */
+  onPrefChanged(changedPref) {
+    // Null out this._engines when the local-one-offs-related prefs change so
+    // that they rebuild themselves the next time the view opens.
+    let prefs = [...LOCAL_MODES.values()].map(({ pref }) => pref);
+    prefs.push("update2", "update2.localOneOffs", "update2.oneOffsRefresh");
+    if (prefs.includes(changedPref)) {
+      this._engines = null;
+    }
+  }
+
   /**
    * Overrides _rebuildEngineList to add the local one-offs.
    *
@@ -251,21 +265,4 @@ class UrlbarSearchOneOffs extends SearchOneOffs {
 
     this.handleSearchCommand(event, engineOrSource);
   }
-
-  /**
-   * Called when a pref tracked by UrlbarPrefs changes.
-   *
-   * @param {string} changedPref
-   *   The name of the pref, relative to `browser.urlbar.` if the pref is in
-   *   that branch.
-   */
-  _onPrefChanged(changedPref) {
-    // Null out this._engines when the local-one-offs-related prefs change so
-    // that they rebuild themselves the next time the view opens.
-    let prefs = [...LOCAL_MODES.values()].map(({ pref }) => pref);
-    prefs.push("update2", "update2.localOneOffs", "update2.oneOffsRefresh");
-    if (prefs.includes(changedPref)) {
-      this._engines = null;
-    }
-  }
 }