Use value of fields for query.

Author: peterwilsoncc

src/wp-includes/class-wp-query.php

@@ -3776,12 +3776,12 @@ public function the_post() {
 		$post = $this->next_post();
 
 		// Ensure a full post object is available.
-		if ( $post instanceof stdClass ) {
-			// stdClass indicates that a partial post object was queried.
-			$post = get_post( $post->ID );
-		} elseif ( is_numeric( $post ) ) {
-			// Numeric indicates that only post IDs were queried.
+		if ( 'ids' === $this->query_vars['fields'] ) {
+			// Post IDs queried.
 			$post = get_post( $post );
+		} elseif ( 'all' !== $this->query_vars['fields'] ) {
+			// Partial object (stdClass) queried.
+			$post = get_post( $post->ID );
 		}
 
 		// Set up the global post object for the loop.