Fix fatal error when resetting an already deleted role (#57)

Author: danielbachhuber

features/roles.feature

@@ -111,6 +111,37 @@ Feature: Manage WordPress roles
       Success: Role reset.
       """
 
+  Scenario: Resetting an already-deleted role
+    Given a WP install
+
+    When I run `wp role delete editor`
+    Then STDOUT should be:
+      """
+      Success: Role with key 'editor' deleted.
+      """
+
+    When I try `wp role exists editor`
+    Then STDERR should be:
+      """
+      Error: Role with ID 'editor' does not exist.
+      """
+
+    When I run `wp role reset editor`
+    Then STDOUT should contain:
+      """
+      removed 0 capabilities from 'editor' role.
+      """
+    And STDOUT should contain:
+      """
+      Success: Role reset.
+      """
+
+    When I run `wp role exists editor`
+    Then STDOUT should be:
+      """
+      Success: Role with ID 'editor' exists.
+      """
+
   Scenario: Cloning a role
     When I try `wp role create reporter Reporter --clone=no-role`
     Then STDERR should be:

src/Role_Command.php

@@ -359,13 +359,14 @@ public function reset( $args, $assoc_args ) {
 			// phpcs:ignore WordPress.PHP.StrictComparisons.LooseComparison -- Object instances won't be same, strict check will fail here.
 			if ( $after[ $role_key ] != $before[ $role_key ] ) {
 				++$num_reset;
-				$restored_cap       = array_diff_key( $after[ $role_key ]->capabilities, $before[ $role_key ]->capabilities );
-				$removed_cap        = array_diff_key( $before[ $role_key ]->capabilities, $after[ $role_key ]->capabilities );
-				$restored_cap_count = count( $restored_cap );
-				$removed_cap_count  = count( $removed_cap );
-				$restored_text      = ( 1 === $restored_cap_count ) ? '%d capability' : '%d capabilities';
-				$removed_text       = ( 1 === $removed_cap_count ) ? '%d capability' : '%d capabilities';
-				$message            = "Restored {$restored_text} to and removed {$removed_text} from '%s' role.";
+				$before_capabilities = isset( $before[ $role_key ] ) ? $before[ $role_key ]->capabilities : [];
+				$restored_cap        = array_diff_key( $after[ $role_key ]->capabilities, $before_capabilities );
+				$removed_cap         = array_diff_key( $before_capabilities, $after[ $role_key ]->capabilities );
+				$restored_cap_count  = count( $restored_cap );
+				$removed_cap_count   = count( $removed_cap );
+				$restored_text       = ( 1 === $restored_cap_count ) ? '%d capability' : '%d capabilities';
+				$removed_text        = ( 1 === $removed_cap_count ) ? '%d capability' : '%d capabilities';
+				$message             = "Restored {$restored_text} to and removed {$removed_text} from '%s' role.";
 				WP_CLI::log( sprintf( $message, $restored_cap_count, $removed_cap_count, $role_key ) );
 			} else {
 				WP_CLI::log( "No changes necessary for '{$role_key}' role." );