Introduce heuristic for identifying "primary" nav location in a theme.

This is important when creating default nav menu items in site
templates, and then copying those values into sites created from
those templates.

See cuny-academic-commons/commons-in-a-box#462.

classes/Upgrades/NavMenus.php

@@ -100,8 +100,9 @@ public function process( $item ) {
 
 		switch_to_blog( $site_id );
 
-		$locations = get_theme_mod( 'nav_menu_locations' );
-		$menu_id   = isset( $locations['primary'] ) ? (int) $locations['primary'] : 0;
+		$locations       = get_theme_mod( 'nav_menu_locations' );
+		$primary_nav_key = cboxol_get_theme_primary_nav_menu_location();
+		$menu_id         = isset( $locations[ $primary_nav_key ] ) ? (int) $locations[ $primary_nav_key ] : 0;
 
 		if ( ! $menu_id ) {
 			restore_current_blog();

includes/group-sites.php

@@ -1820,9 +1820,10 @@ function( $v ) use ( $source_site_url, $source_site_upload_dir, $dest_site_url,
 				}
 
 				// Updated custom nav menu items
-				$locations = get_theme_mod( 'nav_menu_locations' );
-				$menu_id   = isset( $locations['primary'] ) ? (int) $locations['primary'] : 0;
-				$nav_items = get_term_meta( $menu_id, 'cboxol_custom_menus', true );
+				$primary_nav_key = cboxol_get_theme_primary_nav_menu_location();
+				$locations       = get_theme_mod( 'nav_menu_locations' );
+				$menu_id         = isset( $locations[ $primary_nav_key ] ) ? (int) $locations[ $primary_nav_key ] : 0;
+				$nav_items       = get_term_meta( $menu_id, 'cboxol_custom_menus', true );
 
 				if ( $menu_id && ! empty( $nav_items ) ) {
 					$group_type = cboxol_get_group_group_type( $group_id );
@@ -2127,6 +2128,32 @@ function cboxol_get_nav_menu_items() {
 	return $items;
 }
 
+/**
+ * Determine a theme's primary nav menu location.
+ *
+ * Uses a heuristic based on naming conventions, and falls back on the first available.
+ *
+ * @since 1.6.0
+ *
+ * @return string|null
+ */
+function cboxol_get_theme_primary_nav_menu_location() {
+	$keys_to_check = [ 'primary', 'main', 'header', 'top' ];
+
+	$locations = get_nav_menu_locations();
+	if ( ! $locations ) {
+		return null;
+	}
+
+	foreach ( $keys_to_check as $key ) {
+		if ( isset( $locations[ $key ] ) ) {
+			return $key;
+		}
+	}
+
+	return key( $locations );
+}
+
 /**
  * Register meta box for CBOX OpenLab nav menu.
  *

includes/site-template.php

@@ -665,8 +665,9 @@ function cboxol_create_site_for_template( $template_id, $slug, $name ) {
 		true
 	);
 
-	$locations            = get_theme_mod( 'nav_menu_locations' );
-	$locations['primary'] = $menu_id;
+	$primary_nav_key               = cboxol_get_theme_primary_nav_menu_location();
+	$locations                     = get_theme_mod( 'nav_menu_locations' );
+	$locations[ $primary_nav_key ] = $menu_id;
 	set_theme_mod( 'nav_menu_locations', $locations );
 
 	restore_current_blog();