Correctly mark email as optional

Look at the flows to see if there is one we can complete without
an email address. Mark the email address as optional iff there is.

src/components/structures/login/Registration.js

@@ -93,6 +93,7 @@ module.exports = React.createClass({
             doingUIAuth: Boolean(this.props.sessionId),
             hsUrl: this.props.customHsUrl,
             isUrl: this.props.customIsUrl,
+            flows: null,
         };
     },
 
@@ -145,11 +146,27 @@ module.exports = React.createClass({
         });
     },
 
-    _replaceClient: function() {
+    _replaceClient: async function() {
         this._matrixClient = Matrix.createClient({
             baseUrl: this.state.hsUrl,
             idBaseUrl: this.state.isUrl,
         });
+        try {
+            const result = await this._makeRegisterRequest({});
+            // This should never succeed since we specified an empty
+            // auth object.
+            console.log("Expecting 401 from register request but got success!");
+        } catch (e) {
+            if (e.httpStatus === 401) {
+                this.setState({
+                    flows: e.data.flows,
+                });
+            } else {
+                this.setState({
+                    errorText: _t("Unable to query for supported registration methods"),
+                });
+            }
+        }
     },
 
     onFormSubmit: function(formVals) {
@@ -378,7 +395,7 @@ module.exports = React.createClass({
                     poll={true}
                 />
             );
-        } else if (this.state.busy || this.state.teamServerBusy) {
+        } else if (this.state.busy || this.state.teamServerBusy || !this.state.flows) {
             registerBody = <Spinner />;
         } else {
             let serverConfigSection;
@@ -408,6 +425,7 @@ module.exports = React.createClass({
                         onError={this.onFormValidationFailed}
                         onRegisterClick={this.onFormSubmit}
                         onTeamSelected={this.onTeamSelected}
+                        flows={this.state.flows}
                     />
                     { serverConfigSection }
                 </div>

src/components/views/login/RegistrationForm.js

@@ -1,6 +1,7 @@
 /*
 Copyright 2015, 2016 OpenMarket Ltd
 Copyright 2017 Vector Creations Ltd
+Copyright 2018 New Vector Ltd
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -49,7 +50,7 @@ module.exports = React.createClass({
         teamsConfig: PropTypes.shape({
             // Email address to request new teams
             supportEmail: PropTypes.string,
-            teams: PropTypes.arrayOf(React.PropTypes.shape({
+            teams: PropTypes.arrayOf(PropTypes.shape({
                 // The displayed name of the team
                 "name": PropTypes.string,
                 // The domain of team email addresses
@@ -60,6 +61,7 @@ module.exports = React.createClass({
         minPasswordLength: PropTypes.number,
         onError: PropTypes.func,
         onRegisterClick: PropTypes.func.isRequired, // onRegisterClick(Object) => ?Promise
+        flows: PropTypes.arrayOf(PropTypes.object),
     },
 
     getDefaultProps: function() {
@@ -273,12 +275,18 @@ module.exports = React.createClass({
         });
     },
 
+    _authStepIsRequired(step) {
+        // A step is required if no flow exists which does not include that step
+        // (Notwithstanding setups like either email or msisdn being required)
+        return !this.props.flows.some((flow) => {
+            return !flow.stages.includes(step);
+        });
+    },
+
     render: function() {
         const self = this;
 
-        const theme = SettingsStore.getValue("theme");
-        // FIXME: remove hardcoded Status team tweaks at some point
-        const emailPlaceholder = theme === 'status' ? _t("Email address") : _t("Email address (optional)");
+        const emailPlaceholder = this._authStepIsRequired('m.login.email.identity') ? _t("Email address") : _t("Email address (optional)");
 
         const emailSection = (
             <div>
@@ -315,6 +323,7 @@ module.exports = React.createClass({
         const CountryDropdown = sdk.getComponent('views.login.CountryDropdown');
         let phoneSection;
         if (!SdkConfig.get().disable_3pid_login) {
+            const phonePlaceholder = this._authStepIsRequired('m.login.msisdn') ? _t("Mobile phone number") : _t("Mobile phone number (optional)");
             phoneSection = (
                 <div className="mx_Login_phoneSection">
                     <CountryDropdown ref="phone_country" onOptionChange={this._onPhoneCountryChange}
@@ -324,7 +333,7 @@ module.exports = React.createClass({
                         showPrefix={true}
                     />
                     <input type="text" ref="phoneNumber"
-                        placeholder={_t("Mobile phone number (optional)")}
+                        placeholder={phonePlaceholder}
                         defaultValue={this.props.defaultPhoneNumber}
                         className={this._classForField(
                             FIELD_PHONE_NUMBER,