Mind discarded status of tabs when internally handling them

Related discussion:
- https://bugzilla.mozilla.org/show_bug.cgi?id=1652925#c19

Content scripts should not be injected in discarded tabs, and
a discarded tab should treated as if it does not exist.

src/js/start.js

@@ -52,38 +52,45 @@ vAPI.app.onShutdown = function() {
 // the extension was launched. It can be used to inject content scripts
 // in already opened web pages, to remove whatever nuisance could make it to
 // the web pages before uBlock was ready.
+//
+// https://bugzilla.mozilla.org/show_bug.cgi?id=1652925#c19
+//   Mind discarded tabs.
 
 const initializeTabs = async function() {
     const manifest = browser.runtime.getManifest();
     if ( manifest instanceof Object === false ) { return; }
 
-    const tabs = await vAPI.tabs.query({ url: '<all_urls>' });
     const toCheck = [];
-    const checker = {
+    const tabIds = [];
-        file: 'js/scriptlets/should-inject-contentscript.js'
+    {
-    };
+        const checker = { file: 'js/scriptlets/should-inject-contentscript.js' };
+        const tabs = await vAPI.tabs.query({ url: '<all_urls>' });
         for ( const tab of tabs  ) {
-        µb.tabContextManager.commit(tab.id, tab.url);
+            if ( tab.discarded === true ) { continue; }
-        µb.bindTabToPageStats(tab.id);
+            const { id, url } = tab;
+            µb.tabContextManager.commit(id, url);
+            µb.bindTabToPageStats(id);
             // https://github.com/chrisaljoudi/uBlock/issues/129
             //   Find out whether content scripts need to be injected
             //   programmatically. This may be necessary for web pages which
             //   were loaded before uBO launched.
             toCheck.push(
-            /^https?:\/\//.test(tab.url)
+                /^https?:\/\//.test(url)
-                ? vAPI.tabs.executeScript(tab.id, checker)
+                    ? vAPI.tabs.executeScript(id, checker)
+                               .then(result => result, ( ) => false) 
                     : false
             );
+            tabIds.push(id);
+        }
     }
     const results = await Promise.all(toCheck);
     for ( let i = 0; i < results.length; i++ ) {
         const result = results[i];
         if ( result.length === 0 || result[0] !== true ) { continue; }
-        // Inject dclarative content scripts programmatically.
+        // Inject declarative content scripts programmatically.
-        const tabId = tabs[i].id;
         for ( const contentScript of manifest.content_scripts ) {
             for ( const file of contentScript.js ) {
-                vAPI.tabs.executeScript(tabId, {
+                vAPI.tabs.executeScript(tabIds[i], {
                     file: file,
                     allFrames: contentScript.all_frames,
                     runAt: contentScript.run_at

src/js/tab.js

@@ -577,26 +577,22 @@ housekeep itself.
         tabContexts.delete(this.tabId);
     };
 
-    TabContext.prototype.onTab = function(tab) {
-        if ( tab ) {
-            this.gcTimer = vAPI.setTimeout(( ) => this.onGC(), gcPeriod);
-        } else {
-            this.destroy();
-        }
-    };
-
     TabContext.prototype.onGC = async function() {
         if ( vAPI.isBehindTheSceneTabId(this.tabId) ) { return; }
         // https://github.com/gorhill/uBlock/issues/1713
         //   For unknown reasons, Firefox's setTimeout() will sometimes
         //   causes the callback function to be called immediately, bypassing
-        // the main event loop. For now this should prevent uBO from crashing
+        //   the main event loop. For now this should prevent uBO from
-        // as a result of the bad setTimeout() behavior.
+        //   crashing as a result of the bad setTimeout() behavior.
         if ( this.onGCBarrier ) { return; }
         this.onGCBarrier = true;
         this.gcTimer = null;
         const tab = await vAPI.tabs.get(this.tabId);
-        this.onTab(tab);
+        if ( tab instanceof Object === false || tab.discarded === true ) {
+            this.destroy();
+        } else {
+            this.gcTimer = vAPI.setTimeout(( ) => this.onGC(), gcPeriod);
+        }
         this.onGCBarrier = false;
     };
 
@@ -1074,23 +1070,19 @@ vAPI.tabs = new vAPI.Tabs();
 /******************************************************************************/
 
 µBlock.updateTitle = (( ) => {
-    const tabIdToTimer = new Map();
+    const tabIdToCount = new Map();
     const delay = 499;
 
-    const tryAgain = function(entry) {
+    const updateTitle = async function(tabId) {
-        if ( entry.count === 1 ) { return false; }
+        let count = tabIdToCount.get(tabId);
-        entry.count -= 1;
+        if ( count === undefined ) { return; }
-        tabIdToTimer.set(
+        tabIdToCount.delete(tabId);
-            entry.tabId,
+        const tab = await vAPI.tabs.get(tabId);
-            vAPI.setTimeout(( ) => { updateTitle(entry); }, delay)
+        if ( tab instanceof Object === false || tab.discarded === true ) {
-        );
+            return;
-        return true;
+        }
-    };
-
-    const onTabReady = function(entry, tab) {
-        if ( !tab ) { return; }
         const µb = µBlock;
-        const pageStore = µb.pageStoreFromTabId(entry.tabId);
+        const pageStore = µb.pageStoreFromTabId(tabId);
         if ( pageStore === null ) { return; }
         // Firefox needs this: if you detach a tab, the new tab won't have
         // its rawURL set. Concretely, this causes the logger to report an
@@ -1098,35 +1090,32 @@ vAPI.tabs = new vAPI.Tabs();
         // TODO: Investigate for a fix vAPI-side.
         pageStore.rawURL = tab.url;
         µb.pageStoresToken = Date.now();
-        if ( !tab.title && tryAgain(entry) ) { return; }
         // https://github.com/gorhill/uMatrix/issues/225
         //   Sometimes title changes while page is loading.
-        const settled = tab.title && tab.title === pageStore.title;
+        const settled =
+            typeof tab.title === 'string' &&
+            tab.title !== '' &&
+            tab.title === pageStore.title;
         pageStore.title = tab.title || tab.url || '';
-        if ( !settled ) {
+        if ( settled ) { return; }
-            tryAgain(entry);
+        if ( tabIdToCount.has(tabId) ) { return; }
-        }
+        count -= 1;
+        if ( count === 0 ) { return; }
+        tabIdToCount.set(tabId, count);
+        updateTitleAsync(tabId);
     };
 
-    const updateTitle = async function(entry) {
+    const updateTitleAsync = function(tabId) {
-        tabIdToTimer.delete(entry.tabId);
+        vAPI.setTimeout(( ) => { updateTitle(tabId); }, delay);
-        const tab = await vAPI.tabs.get(entry.tabId);
-        onTabReady(entry, tab);
     };
 
     return function(tabId) {
         if ( vAPI.isBehindTheSceneTabId(tabId) ) { return; }
-        const timer = tabIdToTimer.get(tabId);
+        const count = tabIdToCount.get(tabId);
-        if ( timer !== undefined ) {
+        tabIdToCount.set(tabId, 5);
-            clearTimeout(timer);
+        if ( count === undefined ) {
+            updateTitleAsync(tabId);
         }
-        tabIdToTimer.set(
-            tabId,
-            vAPI.setTimeout(
-                updateTitle.bind(null, { tabId: tabId, count: 5 }),
-                delay
-            )
-        );
     };
 })();
 
@@ -1140,13 +1129,14 @@ vAPI.tabs = new vAPI.Tabs();
     let pageStoreJanitorSampleAt = 0;
     let pageStoreJanitorSampleSize = 10;
 
-    const pageStoreJanitor = function() {
-        const tabIds = Array.from(µBlock.pageStores.keys()).sort();
     const checkTab = async tabId => {
         const tab = await vAPI.tabs.get(tabId);
-            if ( tab ) { return; }
+        if ( tab instanceof Object && tab.discarded !== true ) { return; }
         µBlock.unbindTabFromPageStats(tabId);
     };
+
+    const pageStoreJanitor = function() {
+        const tabIds = Array.from(µBlock.pageStores.keys()).sort();
         if ( pageStoreJanitorSampleAt >= tabIds.length ) {
             pageStoreJanitorSampleAt = 0;
         }