Fix setting guild role positions (#751)

src/structures/Guild.js

@@ -630,6 +630,32 @@ class Guild {
     return this.client.rest.methods.deleteGuild(this);
   }
 
+  /**
+   * Set the position of a role in this guild
+   * @param {string|Role} role the role to edit, can be a role object or a role ID.
+   * @param {number} position the new position of the role
+   * @returns {Promise<Guild>}
+   */
+  setRolePosition(role, position) {
+    if (role instanceof Role) {
+      role = role.id;
+    } else if (typeof role !== 'string') {
+      return Promise.reject(new Error('Supplied role is not a role or string'));
+    }
+
+    position = Number(position);
+    if (isNaN(position)) {
+      return Promise.reject(new Error('Supplied position is not a number'));
+    }
+
+    const updatedRoles = this.roles.array().map(r => ({
+      id: r.id,
+      position: r.id === role ? position : (r.position < position ? r.position : r.position + 1),
+    }));
+
+    return this.client.rest.methods.setRolePositions(this.id, updatedRoles);
+  }
+
   /**
    * Whether this Guild equals another Guild. It compares all properties, so for most operations
    * it is advisable to just compare `guild.id === guild2.id` as it is much faster and is often

src/structures/Role.js

@@ -230,7 +230,7 @@ class Role {
    *  .catch(console.error);
    */
   setPosition(position) {
-    return this.client.rest.methods.updateGuildRole(this, { position });
+    return this.guild.setRolePosition(this, position);
   }
 
   /**