Plugins: Ensure proper flags are used with json_encode() (#46117)

This is a best-effort application of proper flags for `json_encode()`
and `wp_json_encode()`.

It also includes some cleanup of PHP 5.2 compatibility
(`JSON.parse(decodeURIComponent())`), which was a workaround for when
the flags we now use did not exist.

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/19936177306

Upstream-Ref: Automattic/jetpack@389e385

Author: anomiex

CHANGELOG.md

@@ -13,6 +13,9 @@ This is an alpha version! The changes listed here are not final.
 - Device Detection: use an embedded version instead of the Composer dependency
 - Update package dependencies.
 
+### Fixed
+- Ensure proper flags are used with `json_encode()`.
+
 ## [3.0.3] - 2025-11-11
 ### Added
 - Tested up to WordPress 6.9. [#45571]

wp-cache-phase2.php

@@ -778,9 +778,9 @@ function wpsc_dump_get_request() {
 	}
 
 	if ( function_exists( 'wp_json_encode' ) ) {
-		$string = wp_json_encode( $_GET );
+		$string = wp_json_encode( $_GET, JSON_UNESCAPED_SLASHES ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
 	} else {
-		$string = json_encode( $_GET );
+		$string = json_encode( $_GET, JSON_UNESCAPED_SLASHES ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended,WordPress.WP.AlternativeFunctions.json_encode_json_encode
 	}
 
 	return $string;
@@ -2947,7 +2947,7 @@ function wp_cache_shutdown_callback() {
 			}
 		}
 
-		$serial = '<?php die(); ?>' . json_encode( $wp_cache_meta );
+		$serial = '<?php die(); ?>' . wp_json_encode( $wp_cache_meta, JSON_UNESCAPED_SLASHES );
 		$dir    = get_current_url_supercache_dir();
 		if ( @is_dir( $dir ) == false ) {
 			@wp_mkdir_p( $dir );

wp-cache.php

@@ -3383,7 +3383,7 @@ function wpsc_update_active_preload( $group = null, $progress = null, $url = nul
 
 	$filename = wpsc_get_preload_status_file_path();
 	// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_file_put_contents
-	if ( false === file_put_contents( $filename, wp_json_encode( $preload_status ) ) ) {
+	if ( false === file_put_contents( $filename, wp_json_encode( $preload_status, JSON_UNESCAPED_SLASHES ) ) ) {
 		wp_cache_debug( "wpsc_update_active_preload: failed to write to $filename" );
 	}
 }
@@ -3403,7 +3403,7 @@ function wpsc_update_idle_preload( $finish_time = null ) {
 
 	$filename = wpsc_get_preload_status_file_path();
 	// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_file_put_contents
-	if ( false === file_put_contents( $filename, wp_json_encode( $preload_status ) ) ) {
+	if ( false === file_put_contents( $filename, wp_json_encode( $preload_status, JSON_UNESCAPED_SLASHES ) ) ) {
 		wp_cache_debug( "wpsc_update_idle_preload: failed to write to $filename" );
 	}
 }