Ticket #57394: 3809.diff

src/wp-includes/user.php

@@ -2112 +2112 @@
                 return new WP_Error( 'user_login_too_long', __( 'Username may not be longer than 60 characters.' ) );
         }
 
+        // Username must be unique.
         if ( ! $update && username_exists( $user_login ) ) {
                 return new WP_Error( 'existing_user_login', __( 'Sorry, that username already exists!' ) );
         }
 
+        // Username must not exist as an existing email.
+        if ( email_exists( $user_login ) ) {
+                return new WP_Error( 'existing_user_login_as_email', __( 'Sorry, that username is not available.' ) );
+        }
+
         /**
          * Filters the list of disallowed usernames.
          *
@@ -3329 +3335 @@
                 $sanitized_user_login = '';
         } elseif ( username_exists( $sanitized_user_login ) ) {
                 $errors->add( 'username_exists', __( '<strong>Error:</strong> This username is already registered. Please choose another one.' ) );
-
+        } elseif ( email_exists( $sanitized_user_login ) ) {
+                $errors->add( 'username_exists_as_email', __( '<strong>Error:</strong> This username is not available. Please choose another one.' ) );
         } else {
                 /** This filter is documented in wp-includes/user.php */
                 $illegal_user_logins = (array) apply_filters( 'illegal_user_logins', array() );