Check the number of h1 elements on block theme templates

checkbase.php

@@ -386,6 +386,7 @@ function tc_adapt_checks_for_fse_themes( $php_files, $css_files, $other_files )
 
 	// Add FSE specific checks.
 	$themechecks[] = new FSE_Required_Files_Check();
+	$themechecks[] = new FSE_Templates_H1_Check();
 
 	return true;
 }

checks/class-fse-templates-h1-check.php

@@ -0,0 +1,91 @@
+<?php
+/**
+ * Checks that Full-Site Editing theme templates have 1 and only 1 h1 tag.
+ *
+ * @package Theme Check
+ */
+
+/**
+ * Class FSE_Templates_H1_Check
+ *
+ * Checks that Full-Site Editing theme templates have 1 and only 1 h1 tag.
+ *
+ * This check is not added to the global array of checks, because it doesn't apply to all themes.
+ */
+class FSE_Templates_H1_Check implements themecheck {
+	/**
+	 * Error messages, warnings and info notices.
+	 *
+	 * @var array $error
+	 */
+	protected $error = array();
+
+	/**
+	 * Check that return true for good/okay/acceptable, false for bad/not-okay/unacceptable.
+	 *
+	 * @param array $php_files File paths and content for PHP files.
+	 * @param array $css_files File paths and content for CSS files.
+	 * @param array $other_files Folder names, file paths and content for other files.
+	 */
+	public function check( $php_files, $css_files, $other_files ) {
+
+		$ret                             = true;
+		$templates                       = get_block_templates();
+		$templates_with_multiple_h1_tags = array();
+		$templates_with_no_h1_tags       = array();
+
+		foreach ( $templates as $template ) {
+			$blocks   = parse_blocks( $template->content );
+			$h1_count = $this->count_h1_tags_recursively( $blocks );
+
+			if ( $h1_count > 1 ) {
+				$templates_with_multiple_h1_tags[] = $template->slug;
+			}
+
+			if ( $h1_count === 0 ) {
+				$templates_with_no_h1_tags[] = $template->slug;
+			}
+		}
+
+		if ( ! empty( $templates_with_multiple_h1_tags ) ) {
+			$this->error[] = sprintf( '<span class="tc-lead tc-warning">' . __( 'WARNING', 'theme-check' ) . '</span>: ' . __( 'The following templates have multiple h1 tags: %s', 'theme-check' ), '<strong>' . implode( ', ', $templates_with_multiple_h1_tags ) . '</strong>' );
+		}
+
+		if ( ! empty( $templates_with_no_h1_tags ) ) {
+			$this->error[] = sprintf( '<span class="tc-lead tc-warning">' . __( 'WARNING', 'theme-check' ) . '</span>: ' . __( 'The following templates have no h1 tags: %s', 'theme-check' ), '<strong>' . implode( ', ', $templates_with_no_h1_tags ) . '</strong>' );
+		}
+
+		return $ret;
+	}
+
+	/**
+	 * Recursively count h1 tags in blocks, including nested blocks.
+	 *
+	 * @param array $blocks Array of blocks to process.
+	 * @return int Number of h1 tags found.
+	 */
+	private function count_h1_tags_recursively( $blocks ) {
+		$h1_count = 0;
+		foreach ( $blocks as $block ) {
+			if ( ! empty( $block['innerBlocks'] ) ) {
+				$h1_count += $this->count_h1_tags_recursively( $block['innerBlocks'] );
+			} else {
+				if ( $block['blockName'] === 'core/heading' || $block['blockName'] === 'core/post-title' ) {
+					if ( isset( $block['attrs']['level'] ) && $block['attrs']['level'] === 1 ) {
+						$h1_count++;
+					}
+				}
+			}
+		}
+		return $h1_count;
+	}
+
+	/**
+	 * Get error messages from the checks.
+	 *
+	 * @return array Error message.
+	 */
+	public function getError() {
+		return $this->error;
+	}
+}