Themes: Report theme as broken that sets itself as its parent.

Props davilera.
Fixes #40820.

Built from https://develop.svn.wordpress.org/trunk@41601


git-svn-id: http://core.svn.wordpress.org/trunk@41436 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-theme.php

@@ -250,6 +250,14 @@ final class WP_Theme implements ArrayAccess {
 			}
 		}
 
+		if ( ! $this->template && $this->stylesheet === $this->headers['Template'] ) {
+			/* translators: %s: Template */
+			$this->errors = new WP_Error( 'theme_child_invalid', sprintf( __( 'The theme defines itself as its parent theme. Please check the "%s" header.' ), 'Template' ) );
+			$this->cache_add( 'theme', array( 'headers' => $this->headers, 'errors' => $this->errors, 'stylesheet' => $this->stylesheet ) );
+
+			return;
+		}
+
 		// (If template is set from cache [and there are no errors], we know it's good.)
 		if ( ! $this->template && ! ( $this->template = $this->headers['Template'] ) ) {
 			$this->template = $this->stylesheet;

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-41600';
+$wp_version = '4.9-alpha-41601';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.