Navigation block: Add an unstable location attribute (#32491)

* Navigation block: Add an unstable location attribute

* Change the signature and name of the function that renders a classic menu

* Use the location parameter when rendering the classic menu

* lint fix

packages/block-library/src/navigation/block.json

@@ -42,6 +42,9 @@
 		"isResponsive": {
 			"type": "boolean",
 			"default": false
+		},
+		"__unstable__location": {
+			"type": "string"
 		}
 	},
 	"providesContext": {

packages/block-library/src/navigation/index.php

@@ -85,6 +85,37 @@ function block_core_navigation_build_css_font_sizes( $attributes ) {
 	return $font_sizes;
 }
 
+/**
+ * Renders a Navigation Block derived from data from the theme_location assigned
+ * via the block attribute 'location'.
+ *
+ * If the theme doesn't explicity support 'block-nav-menus' or no location was provided
+ * as a block attribute then an empty string is returned.
+ *
+ * @param  array $location The location of the classic menu to display.
+ * @param  array $attributes Navigation block attributes.
+ * @return string|false HTML markup of a generated Navigation Block or false if no location is specified.
+ */
+function render_classic_location_menu( $location, $attributes ) {
+	if ( empty( $location ) ) {
+		return false;
+	}
+
+	$block_attributes = $attributes;
+	unset( $block_attributes['__unstable__location'] );
+
+	return wp_nav_menu(
+		array(
+			'theme_location'   => $location,
+			'block_attributes' => $block_attributes,
+			'container'        => '',
+			'items_wrap'       => '%3$s',
+			'fallback_cb'      => false,
+			'echo'             => false,
+		)
+	);
+}
+
 /**
  * Returns the top-level submenu SVG chevron icon.
  *
@@ -133,6 +164,14 @@ function render_block_core_navigation( $attributes, $content, $block ) {
 	}
 
 	if ( empty( $block->inner_blocks ) ) {
+		if ( array_key_exists( '__unstable__location', $attributes ) ) {
+			$location                 = $attributes['__unstable__location'];
+			$maybe_classic_navigation = render_classic_location_menu( $location, $attributes );
+			if ( $maybe_classic_navigation ) {
+				return $maybe_classic_navigation;
+			}
+		}
+
 		return '';
 	}