Fix email registration, pt. 2

Regressed in https://github.com/matrix-org/matrix-react-sdk/pull/2768
where we check for an existing stored account first and restore that
instead if it exist, telling the user. We usually make a guest account
when the user first hits the page though, so this just restored this
guest account.

Don't restore the account if it's just a guest account (which, as per
comment, is not perfect, but is definitely better than the current
behaviour).

Fixes https://github.com/vector-im/riot-web/issues/9581

src/Lifecycle.js

@@ -126,6 +126,15 @@ export function getStoredSessionOwner() {
     return hsUrl && userId && accessToken ? userId : null;
 }
 
+/**
+ * @returns {bool} True if the stored session is for a guest user or false if it is
+ *     for a real user. If there is no stored session, return null.
+ */
+export function getStoredSessionIsGuest() {
+    const {hsUrl, isUrl, accessToken, userId, deviceId, isGuest} = _getLocalStorageSessionVars();
+    return hsUrl && userId && accessToken ? isGuest : null;
+}
+
 /**
  * @param {Object} queryParams    string->string map of the
  *     query-parameters extracted from the real query-string of the starting
@@ -235,7 +244,15 @@ function _getLocalStorageSessionVars() {
     const userId = localStorage.getItem("mx_user_id");
     const deviceId = localStorage.getItem("mx_device_id");
 
-    return {hsUrl, isUrl, accessToken, userId, deviceId};
+    let isGuest;
+    if (localStorage.getItem("mx_is_guest") !== null) {
+        isGuest = localStorage.getItem("mx_is_guest") === "true";
+    } else {
+        // legacy key name
+        isGuest = localStorage.getItem("matrix-is-guest") === "true";
+    }
+
+    return {hsUrl, isUrl, accessToken, userId, deviceId, isGuest};
 }
 
 // returns a promise which resolves to true if a session is found in
@@ -253,15 +270,7 @@ async function _restoreFromLocalStorage() {
         return false;
     }
 
-    const {hsUrl, isUrl, accessToken, userId, deviceId} = _getLocalStorageSessionVars();
-
-    let isGuest;
-    if (localStorage.getItem("mx_is_guest") !== null) {
-        isGuest = localStorage.getItem("mx_is_guest") === "true";
-    } else {
-        // legacy key name
-        isGuest = localStorage.getItem("matrix-is-guest") === "true";
-    }
+    const {hsUrl, isUrl, accessToken, userId, deviceId, isGuest} = _getLocalStorageSessionVars();
 
     if (accessToken && userId && hsUrl) {
         console.log(`Restoring session for ${userId}`);

src/components/structures/MatrixChat.js

@@ -1735,9 +1735,13 @@ export default React.createClass({
     onRegistered: function(credentials) {
         if (this.state.register_session_id) {
             // The user came in through an email validation link. To avoid overwriting
-            // their session, check to make sure the session isn't someone else.
+            // their session, check to make sure the session isn't someone else, and
+            // isn't a guest user since we'll usually have set a guest user session before
+            // starting the registration process. This isn't perfect since it's possible
+            // the user had a separate guest session they didn't actually mean to replace.
             const sessionOwner = Lifecycle.getStoredSessionOwner();
-            if (sessionOwner && sessionOwner !== credentials.userId) {
+            const sessionIsGuest = Lifecycle.getStoredSessionIsGuest();
+            if (sessionOwner && !sessionIsGuest && sessionOwner !== credentials.userId) {
                 console.log(
                     `Found a session for ${sessionOwner} but ${credentials.userId} is trying to verify their ` +
                     `email address. Restoring the session for ${sessionOwner} with warning.`,