Bug 853779 - Ensure we don't lose sessions when starting with a private window only; r=yoric

browser/components/sessionstore/src/SessionSaver.jsm

@@ -202,15 +202,6 @@ let SessionSaverInternal = {
       }
     }
 
-#ifndef XP_MACOSX
-    // Don't save invalid states.
-    // Looks like we currently have private windows, only.
-    if (state.windows.length == 0) {
-      stopWatchCancel("COLLECT_DATA_MS", "COLLECT_DATA_LONGEST_OP_MS");
-      return;
-    }
-#endif
-
     // Remove private windows from the list of closed windows.
     for (let i = state._closedWindows.length - 1; i >= 0; i--) {
       if (state._closedWindows[i].isPrivate) {
@@ -218,6 +209,13 @@ let SessionSaverInternal = {
       }
     }
 
+    // Make sure that we keep the previous session if we started with a single
+    // private window and no non-private windows have been opened, yet.
+    if (state.deferredInitialState) {
+      state.windows = state.deferredInitialState.windows || [];
+      delete state.deferredInitialState;
+    }
+
 #ifndef XP_MACOSX
     // We want to restore closed windows that are marked with _shouldRestore.
     // We're doing this here because we want to control this only when saving

browser/components/sessionstore/src/SessionStore.jsm

@@ -728,7 +728,7 @@ let SessionStoreInternal = {
           // We're starting with a single private window. Save the state we
           // actually wanted to restore so that we can do it later in case
           // the user opens another, non-private window.
-          this._deferredInitialState = aInitialState;
+          this._deferredInitialState = gSessionStartup.state;
 
           // Nothing to restore now, notify observers things are complete.
           Services.obs.notifyObservers(null, NOTIFY_WINDOWS_RESTORED, "");
@@ -1346,6 +1346,9 @@ let SessionStoreInternal = {
     // Don't include the last session state in getBrowserState().
     delete state.lastSessionState;
 
+    // Don't include any deferred initial state.
+    delete state.deferredInitialState;
+
     return this._toJSONString(state);
   },
 
@@ -2074,6 +2077,13 @@ let SessionStoreInternal = {
       state.lastSessionState = this._lastSessionState;
     }
 
+    // If we were called by the SessionSaver and started with only a private
+    // window we want to pass the deferred initial state to not lose the
+    // previous session.
+    if (this._deferredInitialState) {
+      state.deferredInitialState = this._deferredInitialState;
+    }
+
     return state;
   },
 
@@ -3524,6 +3534,14 @@ let SessionStoreInternal = {
    * @returns [defaultState, state]
    */
   _prepDataForDeferredRestore: function ssi_prepDataForDeferredRestore(state) {
+    // Make sure that we don't modify the global state as provided by
+    // nsSessionStartup.state. Converting the object to a JSON string and
+    // parsing it again is the easiest way to do that, although not the most
+    // efficient one. Deferred sessions that don't have automatic session
+    // restore enabled tend to be a lot smaller though so that this shouldn't
+    // be a big perf hit.
+    state = JSON.parse(JSON.stringify(state));
+
     let defaultState = { windows: [], selectedWindow: 1 };
 
     state.selectedWindow = state.selectedWindow || 1;