Bug 1094409 - Explain in the preferences UI the reason when e10s is disabled. r=felipe

browser/components/preferences/in-content/main.js

@@ -92,9 +92,32 @@ var gMainPane = {
     setEventListener("e10sAutoStart", "command",
                      gMainPane.enableE10SChange);
     let e10sCheckbox = document.getElementById("e10sAutoStart");
-    let e10sPref = document.getElementById("browser.tabs.remote.autostart");
-    let e10sTempPref = document.getElementById("e10sTempPref");
-    e10sCheckbox.checked = e10sPref.value || e10sTempPref.value;
+    e10sCheckbox.checked = Services.appinfo.browserTabsRemoteAutostart;
+
+    // If e10s is blocked for some reason unrelated to prefs, we want to disable
+    // the checkbox.
+    if (!Services.appinfo.browserTabsRemoteAutostart) {
+      let e10sBlockedReason = Cc["@mozilla.org/supports-string;1"].createInstance(Ci.nsISupportsString);
+      let appinfo = Services.appinfo.QueryInterface(Ci.nsIObserver);
+      appinfo.observe(e10sBlockedReason, "getE10SBlocked", "")
+      if (e10sBlockedReason.data) {
+        if (e10sBlockedReason.data == "Safe mode") {
+          // If the only reason we're disabled is because of safe mode, then
+          // we want to allow the user to un-toggle the pref.
+          // We're relying on the nsAppRunner code only specifying "Safe mode"
+          // as the reason if the pref is otherwise enabled, and there are no
+          // other reasons to block e10s.
+          // Update the checkbox to reflect the pref state.
+          e10sCheckbox.checked = true;
+        } else {
+          e10sCheckbox.disabled = true;
+          e10sCheckbox.label += " (disabled: " + e10sBlockedReason.data + ")";
+        }
+      }
+    }
+
+    // If E10S is blocked because of safe mode, we want the checkbox to be
+    // enabled
 #endif
 
 #ifdef MOZ_DEV_EDITION

toolkit/xre/nsAppRunner.cpp

@@ -615,6 +615,9 @@ bool gSafeMode = false;
  * singleton.
  */
 class nsXULAppInfo : public nsIXULAppInfo,
+#ifdef NIGHTLY_BUILD
+                     public nsIObserver,
+#endif
 #ifdef XP_WIN
                      public nsIWinAppHelper,
 #endif
@@ -630,6 +633,9 @@ public:
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_NSIXULAPPINFO
   NS_DECL_NSIXULRUNTIME
+#ifdef NIGHTLY_BUILD
+  NS_DECL_NSIOBSERVER
+#endif
 #ifdef MOZ_CRASHREPORTER
   NS_DECL_NSICRASHREPORTER
   NS_DECL_NSIFINISHDUMPINGCALLBACK
@@ -642,6 +648,9 @@ public:
 NS_INTERFACE_MAP_BEGIN(nsXULAppInfo)
   NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIXULRuntime)
   NS_INTERFACE_MAP_ENTRY(nsIXULRuntime)
+#ifdef NIGHTLY_BUILD
+  NS_INTERFACE_MAP_ENTRY(nsIObserver)
+#endif
 #ifdef XP_WIN
   NS_INTERFACE_MAP_ENTRY(nsIWinAppHelper)
 #endif
@@ -842,8 +851,25 @@ nsXULAppInfo::GetProcessID(uint32_t* aResult)
 }
 
 static bool gBrowserTabsRemoteAutostart = false;
+static nsString gBrowserTabsRemoteDisabledReason;
 static bool gBrowserTabsRemoteAutostartInitialized = false;
 
+#ifdef NIGHTLY_BUILD
+NS_IMETHODIMP
+nsXULAppInfo::Observe(nsISupports *aSubject, const char *aTopic, const char16_t *aData) {
+  if (!nsCRT::strcmp(aTopic, "getE10SBlocked")) {
+    nsCOMPtr<nsISupportsString> ret = do_QueryInterface(aSubject);
+    if (!ret)
+      return NS_ERROR_FAILURE;
+
+    ret->SetData(gBrowserTabsRemoteDisabledReason);
+
+    return NS_OK;
+  }
+  return NS_ERROR_FAILURE;
+}
+#endif
+
 NS_IMETHODIMP
 nsXULAppInfo::GetBrowserTabsRemoteAutostart(bool* aResult)
 {
@@ -4538,8 +4564,10 @@ XRE_GetProcessType()
 
 static void
 LogE10sBlockedReason(const char *reason) {
+  gBrowserTabsRemoteDisabledReason.Assign(NS_ConvertASCIItoUTF16(reason));
+
   nsAutoString msg(NS_LITERAL_STRING("==================\nE10s has been blocked from running because:\n"));
-  msg.Append(NS_ConvertASCIItoUTF16(reason));
+  msg.Append(gBrowserTabsRemoteDisabledReason);
   msg.AppendLiteral("\n==================\n");
   nsCOMPtr<nsIConsoleService> console(do_GetService("@mozilla.org/consoleservice;1"));
   if (console) {
@@ -4574,11 +4602,11 @@ mozilla::BrowserTabsRemoteAutostart()
 
   if (prefEnabled) {
     if (gSafeMode) {
-      LogE10sBlockedReason("Firefox is in safe mode.");
+      LogE10sBlockedReason("Safe mode");
     } else if (disabledForA11y) {
-      LogE10sBlockedReason("An accessibility tool is active.");
+      LogE10sBlockedReason("An accessibility tool is active");
     } else if (disabledForIME) {
-      LogE10sBlockedReason("The keyboard being used has activated IME.");
+      LogE10sBlockedReason("The keyboard being used has activated IME");
     } else {
       gBrowserTabsRemoteAutostart = true;
     }
@@ -4635,7 +4663,7 @@ mozilla::BrowserTabsRemoteAutostart()
 
     if (accelDisabled) {
       gBrowserTabsRemoteAutostart = false;
-      LogE10sBlockedReason("Hardware acceleration is disabled.");
+      LogE10sBlockedReason("Hardware acceleration is disabled");
     }
   }
 #endif