Themes: Improve error notice when wp_is_block_theme() is called too early.

This is a follow-up to [59968] which improves error handling for when `wp_is_block_theme()` is called too early. Initially, `_doing_it_wrong()` was called in `WP_Theme::is_block_theme()` was called prior to themes being set up, in order to avoid the bug reported in #63062, where doing so would cause parent themes to not be resolved. After further investigation, the issue is only caused by calling `wp_is_block_theme()` before the root theme directory has been registered (e.g., when called on the `muplugins_loaded` hook).

Moving This error message to `wp_is_block_theme()` when `$GLOBALS['wp_theme_directories']` is empty avoids unnecessary error messages.

Props wildworks, sukhendu2002, SirLouen, dinhtungdu, narenin, joemcgill, peterwilsoncc, afragen.
Fixes #63086. See #63062.

Built from https://develop.svn.wordpress.org/trunk@60037


git-svn-id: http://core.svn.wordpress.org/trunk@59373 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-theme.php

@@ -1576,11 +1576,6 @@ final class WP_Theme implements ArrayAccess {
 	 * @return bool
 	 */
 	public function is_block_theme() {
-		if ( ! did_action( 'setup_theme' ) ) {
-			_doing_it_wrong( __METHOD__, __( 'This method should not be called before themes are set up.' ), '6.8.0' );
-			return false;
-		}
-
 		if ( isset( $this->block_theme ) ) {
 			return $this->block_theme;
 		}

wp-includes/theme.php

@@ -4352,6 +4352,11 @@ function create_initial_theme_features() {
  * @return bool Whether the active theme is a block-based theme or not.
  */
 function wp_is_block_theme() {
+	if ( empty( $GLOBALS['wp_theme_directories'] ) ) {
+		_doing_it_wrong( __FUNCTION__, __( 'This function should not be called before the theme directory is registered.' ), '6.8.0' );
+		return false;
+	}
+
 	return wp_get_theme()->is_block_theme();
 }
 

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.8-beta2-60036';
+$wp_version = '6.8-beta2-60037';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.