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wp-content/plugins/jetpack/modules/canonical-urls.php

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+<?php
+/**
+ * Module Name: Canonical URLs
+ * Module Description: Add canonical URL tags to archive pages to prevent duplicate content in search engines.
+ * Sort Order: 36
+ * First Introduced: 15.6
+ * Requires Connection: No
+ * Requires User Connection: No
+ * Auto Activate: No
+ * Module Tags: Traffic
+ * Feature: Traffic
+ * Additional Search Queries: canonical, seo, duplicate content, woocommerce, archive
+ *
+ * @package automattic/jetpack
+ */
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit( 0 );
+}
+
+// Disable canonical URL output when a conflicting SEO plugin is active.
+add_filter( 'jetpack_disable_canonical_urls', 'jetpack_canonical_urls_check_conflicts' );
+
+/**
+ * Can be used to prevent the Canonical URLs module from outputting canonical tags.
+ *
+ * @module canonical-urls
+ *
+ * @since 15.6
+ *
+ * @param bool $disabled Whether canonical URL output is disabled. Defaults to false.
+ */
+if ( ! apply_filters( 'jetpack_disable_canonical_urls', false ) ) {
+	require_once __DIR__ . '/canonical-urls/class-jetpack-canonical-urls-resolver.php';
+	add_action( 'wp_head', 'jetpack_canonical_urls_output_tag' );
+}
+
+/**
+ * Check if a conflicting SEO plugin is active and disable canonical URL output.
+ *
+ * @since 15.6
+ *
+ * @param bool $disabled Whether canonical URL output is already disabled.
+ * @return bool Whether canonical URL output should be disabled.
+ */
+function jetpack_canonical_urls_check_conflicts( $disabled ) {
+	if ( $disabled ) {
+		return $disabled;
+	}
+
+	$conflicting_plugins = array(
+		'wordpress-seo/wp-seo.php',
+		'wordpress-seo-premium/wp-seo-premium.php',
+		'all-in-one-seo-pack/all_in_one_seo_pack.php',
+		'all-in-one-seo-pack-pro/all_in_one_seo_pack.php',
+		'seo-by-rank-math/rank-math.php',
+		'autodescription/autodescription.php',
+		'slim-seo/slim-seo.php',
+		'wp-seopress/seopress.php',
+		'wp-seopress-pro/seopress-pro.php',
+		'seo-key/seo-key.php',
+		'seo-key-pro/seo-key.php',
+	);
+
+	foreach ( $conflicting_plugins as $plugin ) {
+		if ( Jetpack::is_plugin_active( $plugin ) ) {
+			return true;
+		}
+	}
+
+	return $disabled;
+}
+
+/**
+ * Output the canonical link tag for non-singular pages.
+ *
+ * WordPress core handles singular posts/pages via rel_canonical(),
+ * so this function only outputs canonical tags for archive pages.
+ *
+ * @since 15.6
+ */
+function jetpack_canonical_urls_output_tag() {
+	if ( is_singular() ) {
+		return;
+	}
+
+	$url = Jetpack_Canonical_Urls_Resolver::get_canonical_url();
+
+	if ( ! empty( $url ) ) {
+		echo '<link rel="canonical" href="' . esc_url( $url ) . '" />' . "\n";
+	}
+}