feat: add ACP option to require email address on new registration

public/language/en-GB/admin/settings/email.json

@@ -37,6 +37,8 @@
 	"subscriptions.hour": "Digest Hour",
 	"subscriptions.hour-help": "Please enter a number representing the hour to send scheduled email digests (e.g. <code>0</code> for midnight, <code>17</code> for 5:00pm). Keep in mind that this is the hour according to the server itself, and may not exactly match your system clock.<br /> The approximate server time is: <span id=\"serverTime\"></span><br /> The next daily digest is scheduled to be sent  <span id=\"nextDigestTime\"></span>",
 	"notifications.remove-images": "Remove images from email notifications",
+	"require-email-address": "Require new users to specify an email address",
+	"require-email-address-warning": "By default, users can opt-out of entering an email address. Enabling this option means they have to enter an email address in order to proceed with registration. <strong>It does not ensure user will enter a real email address, nor even an address they own.</strong>",
 	"include-unverified-emails": "Send emails to recipients who have not explicitly confirmed their emails",
 	"include-unverified-warning": "By default, users with emails associated with their account have already been verified, but there are situations where this is not the case (e.g. SSO logins, grandfathered users, etc). <strong>Enable this setting at your own risk</strong> &ndash; sending emails to unverified addresses may be a violation of regional anti-spam laws."
 }

src/user/interstitials.js

@@ -57,9 +57,15 @@ Interstitials.email = async (data) => {
 						// User attempting to edit another user's email -- not allowed
 						throw new Error('[[error:no-privileges]]');
 					}
-				} else if (current) {
-					// User explicitly clearing their email
-					await user.email.remove(userData.uid, data.req.session.id);
+				} else {
+					if (meta.config.requireEmailAddress) {
+						throw new Error('[[error:invalid-email]]');
+					}
+
+					if (current) {
+						// User explicitly clearing their email
+						await user.email.remove(userData.uid, data.req.session.id);
+					}
 				}
 			} else {
 				// New registrants have the confirm email sent from user.create()

src/views/admin/settings/email.tpl

@@ -27,6 +27,14 @@
 				</label>
 			</div>
 
+			<div class="checkbox">
+				<label for="requireEmailAddress" class="mdl-switch mdl-js-switch mdl-js-ripple-effect">
+					<input class="mdl-switch__input" type="checkbox" id="requireEmailAddress" data-field="requireEmailAddress" name="requireEmailAddress" />
+					<span class="mdl-switch__label">[[admin/settings/email:require-email-address]]</span>
+				</label>
+			</div>
+			<p class="help-block">[[admin/settings/email:require-email-address-warning]]</p>
+
 			<div class="checkbox">
 				<label for="includeUnverifiedEmails" class="mdl-switch mdl-js-switch mdl-js-ripple-effect">
 					<input class="mdl-switch__input" type="checkbox" id="includeUnverifiedEmails" data-field="includeUnverifiedEmails" name="includeUnverifiedEmails" />