Menus: Stop a nested loop clobbering the slug it is matching against.

src/wp-includes/nav-menu.php

@@ -1288,13 +1288,17 @@ function wp_map_nav_menu_locations( $new_nav_menu_locations, $old_nav_menu_locat
 				// Then see if any of the old locations...
 				foreach ( $old_nav_menu_locations as $location => $menu_id ) {
 
-					// ...and any slug in the same group...
-					foreach ( $slug_group as $slug ) {
+					/*
+					 * ...and any slug in the same group. This uses its own variable
+					 * because the outer loop's $slug is still needed for the
+					 * remaining new locations once this one is done.
+					 */
+					foreach ( $slug_group as $old_slug ) {
 
 						// ... have a match as well.
-						if ( is_string( $location ) && false === stripos( $location, $slug ) && false === stripos( $slug, $location ) ) {
+						if ( is_string( $location ) && false === stripos( $location, $old_slug ) && false === stripos( $old_slug, $location ) ) {
 							continue;
-						} elseif ( is_numeric( $location ) && $location !== $slug ) {
+						} elseif ( is_numeric( $location ) && $location !== $old_slug ) {
 							continue;
 						}
 
@@ -1310,7 +1314,7 @@ function wp_map_nav_menu_locations( $new_nav_menu_locations, $old_nav_menu_locat
 							// Go back and check the next new menu location.
 							continue 3;
 						}
-					} // End foreach ( $slug_group as $slug ).
+					} // End foreach ( $slug_group as $old_slug ).
 				} // End foreach ( $old_nav_menu_locations as $location => $menu_id ).
 			} // End foreach foreach ( $registered_nav_menus as $new_location => $name ).
 		} // End foreach ( $slug_group as $slug ).

tests/phpunit/tests/menu/nav-menu.php

@@ -179,6 +179,35 @@ public function test_location_guessing_one_menu_per_location() {
 		$this->assertSame( $expected_nav_menu_locations, $new_next_theme_nav_menu_locations );
 	}
 
+	/**
+	 * A new location that matches only one slug in its group should still be mapped
+	 * after an earlier location in the same group has been mapped.
+	 *
+	 * 'primary-menu' matches 'primary' and nothing else in that group, so unlike
+	 * 'main' in the test above it has no later slug to be picked up by.
+	 *
+	 * @ticket 65884
+	 *
+	 * @covers ::wp_map_nav_menu_locations
+	 */
+	public function test_location_guessing_after_an_earlier_location_in_the_group_matched() {
+		$this->register_nav_menu_locations( array( 'primary', 'primary-menu' ) );
+
+		$prev_theme_nav_menu_locations = array(
+			'header'   => 1,
+			'mainmenu' => 2,
+		);
+
+		$old_next_theme_nav_menu_locations = array();
+		$new_next_theme_nav_menu_locations = wp_map_nav_menu_locations( $old_next_theme_nav_menu_locations, $prev_theme_nav_menu_locations );
+
+		$expected_nav_menu_locations = array(
+			'primary'      => 1,
+			'primary-menu' => 2,
+		);
+		$this->assertSame( $expected_nav_menu_locations, $new_next_theme_nav_menu_locations );
+	}
+
 	/**
 	 * Technically possible to register menu locations numerically.
 	 *