warn users that changing/resetting password will nuke E2E keys

src/components/structures/login/ForgotPassword.js

@@ -87,12 +87,28 @@ module.exports = React.createClass({
             this.showErrorDialog("New passwords must match each other.");
         }
         else {
+            var QuestionDialog = sdk.getComponent("dialogs.QuestionDialog");
+            Modal.createDialog(QuestionDialog, {
+                title: "Warning",
+                description:
+                    <div>
+                        Resetting password will currently reset any end-to-end encryption keys on all devices,
+                        making encrypted chat history unreadable.
+                        In future this <a href="https://github.com/vector-im/riot-web/issues/2671">may be improved</a>,
+                        but for now be warned.
+                    </div>,
+                button: "Continue",
+                onFinished: (confirmed) => {
+                    if (confirmed) {
                         this.submitPasswordReset(
                             this.state.enteredHomeserverUrl, this.state.enteredIdentityServerUrl,
                             this.state.email, this.state.password
                         );
                     }
                 },
+            });
+        }
+    },
 
     onInputChanged: function(stateKey, ev) {
         this.setState({

src/components/views/settings/ChangePassword.js

@@ -18,6 +18,7 @@ limitations under the License.
 
 var React = require('react');
 var MatrixClientPeg = require("../../../MatrixClientPeg");
+var Modal = require("../../../Modal");
 var sdk = require("../../../index");
 
 module.exports = React.createClass({
@@ -65,6 +66,19 @@ module.exports = React.createClass({
     changePassword: function(old_password, new_password) {
         var cli = MatrixClientPeg.get();
 
+        var QuestionDialog = sdk.getComponent("dialogs.QuestionDialog");
+        Modal.createDialog(QuestionDialog, {
+            title: "Warning",
+            description:
+                <div>
+                    Changing password will currently reset any end-to-end encryption keys on all devices,
+                    making encrypted chat history unreadable.
+                    This will be <a href="https://github.com/vector-im/riot-web/issues/2671">improved shortly</a>,
+                    but for now be warned.
+                </div>,
+            button: "Continue",
+            onFinished: (confirmed) => {
+                if (confirmed) {
                     var authDict = {
                         type: 'm.login.password',
                         user: cli.credentials.userId,
@@ -85,6 +99,9 @@ module.exports = React.createClass({
                             phase: self.Phases.Edit
                         });
                     }).done();
+                }
+            },
+        });
     },
 
     onClickChange: function() {