Blocks: Introduce WP_Block_Type and WP_Block_Type_Registry classes.

These are the foundational classes allowing blocks to be registered and used throughout WordPress.

This commit also includes the `has_block()` and `has_blocks()` functions, which are required for unit testing these classes.

Merges [43742] from the 5.0 branch to trunk.

Props adamsilverstein, danielbachhuber, desrosj.
Fixes #45097.
See #45109.


git-svn-id: https://develop.svn.wordpress.org/trunk@44108 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/blocks.php

@@ -0,0 +1,61 @@
+<?php
+/**
+ * Functions related to registering and parsing blocks.
+ *
+ * @package WordPress
+ * @subpackage Blocks
+ * @since 5.0.0
+ */
+
+/**
+ * Determine whether a post or content string has blocks.
+ *
+ * This test optimizes for performance rather than strict accuracy, detecting
+ * the pattern of a block but not validating its structure. For strict accuracy,
+ * you should use the block parser on post content.
+ *
+ * @since 5.0.0
+ * @see parse_blocks()
+ *
+ * @param int|string|WP_Post|null $post Optional. Post content, post ID, or post object. Defaults to global $post.
+ * @return bool Whether the post has blocks.
+ */
+function has_blocks( $post = null ) {
+	if ( ! is_string( $post ) ) {
+		$wp_post = get_post( $post );
+		if ( $wp_post instanceof WP_Post ) {
+			$post = $wp_post->post_content;
+		}
+	}
+
+	return false !== strpos( (string) $post, '<!-- wp:' );
+}
+
+/**
+ * Determine whether a $post or a string contains a specific block type.
+ *
+ * This test optimizes for performance rather than strict accuracy, detecting
+ * the block type exists but not validating its structure. For strict accuracy,
+ * you should use the block parser on post content.
+ *
+ * @since 5.0.0
+ * @see parse_blocks()
+ *
+ * @param string                  $block_type Full Block type to look for.
+ * @param int|string|WP_Post|null $post Optional. Post content, post ID, or post object. Defaults to global $post.
+ * @return bool Whether the post content contains the specified block.
+ */
+function has_block( $block_type, $post = null ) {
+	if ( ! has_blocks( $post ) ) {
+		return false;
+	}
+
+	if ( ! is_string( $post ) ) {
+		$wp_post = get_post( $post );
+		if ( $wp_post instanceof WP_Post ) {
+			$post = $wp_post->post_content;
+		}
+	}
+
+	return false !== strpos( $post, '<!-- wp:' . $block_type . ' ' );
+}