id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc	focuses	prnumber
47699	Remove redundant JSON polyfills for PHP native functionality	jrf	desrosj	"Now the new minimum PHP requirement for WordPress is PHP 5.6.20, the JSON functionality related polyfills for the native PHP functions and related work-arounds can be removed.

I will add a patch for this to this ticket.

Let's talk through it all:

== **Current implementation**

WP polyfills the following PHP native JSON functionality:
* The function [https://www.php.net/manual/en/function.json-encode.php `json_encode()`] (PHP 5.2.0+)
* The function [https://www.php.net/manual/en/function.json-decode.php `json_decode()`] (PHP 5.2.0+)
* The function [https://www.php.net/manual/en/function.json-last-error-msg.php `json_last_error_msg()`] (PHP 5.5.0+)
* The constant [https://www.php.net/manual/en/json.constants.php#constant.json-pretty-print `JSON_PRETTY_PRINT`] (PHP 5.4.0+)
* The constant [https://www.php.net/manual/en/json.constants.php#constant.json-error-none `JSON_ERROR_NONE`] (as part of `json_last_error_msg()`) (PHP 5.3.0+)
* The interface [https://www.php.net/manual/en/class.jsonserializable.php `JsonSerializable`] (PHP 5.4.0+)

In addition to this, it:
* adds the `_json_decode_object_helper()`function, the `WP_JSON_SERIALIZE_COMPATIBLE` constant and the `$wp_json` global variable in the `wp-includes/compat.php` file.
* contains various work-arounds for differences between PHP versions in the `wp_json_encode()` function in the `wp-includes/functions.php` file, including the `_wp_json_prepare_data()` function which is 100% work-around code.
* adds various constants, a `Services_JSON` and a `Services_JSON_Error` class in the `wp-includes/class-json.php` file


== **Why all of the above can be safely deprecated/removed**

=== **Step 1**

As of PHP 5.2.0, the [https://www.php.net/manual/en/json.installation.php JSON extension is bundled and compiled with PHP by default] and can not be disabled.

This means in effect that the following code has not been used since WP 3.3.0 when the minimum PHP requirement went up to PHP 5.2.6:
* `json_encode()` polyfill, including the dummy copy in `wp-admin/includes/noop.php`
* `json_decode()` polyfill
* `_json_decode_object_helper()` function which would only be declared if the PHP native `json_decode()` function didn't exist and was used exclusively by that polyfill.
* `$wp_json` variable as it would only be assigned a value if the PHP native `json_encode()` and `json_decode()` functions didn't exist.
* All of the code in the `wp-includes/class-json.php` file.
* The associated `test_json_encode_decode()` unit test.

With the above in mind, there can be no discussion about removing the first two polyfills - `json_encode()` and `json_decode()` -.

As for removing the `_json_decode_object_helper()`, `$wp_json` and the code in the `wp-includes/class-json.php` file:
As those were only available conditionally, any userland code referring to this function/variable/these classes/constants, would already have to have been surrounded by appropriate `function_exists()`, `class_exists()`, `defined()` or an `isset()` calls.

So, having said that, IMO it is safe to remove all of this.

I'm making one caveat, namely that while the code in the `wp-includes/class-json.php` file can be safely removed, the file itself should probably remain (for now) and should generate a ''deprecated file'' notice just in case a userland plugin/theme would require it directly, though if they do, they've already had eight years to remove that file-include and they will run into trouble now that the code in the file has been removed, but in my estimation, it would be exceedingly rare, most likely non-existent, for any plugin/theme to include this file directly.


=== **Step 2**

Now, as the minimum PHP requirement for WP is now 5.6.20, we can also safely remove:
* the `json_last_error_msg()` polyfill
* the `JSON_PRETTY_PRINT` constant polyfill
* the `JSON_ERROR_NONE` constant polyfill
* the `JsonSerializable` polyfill
* any and all work-arounds for differences between PHP versions regarding `json_encode()`
* any and all work-arounds for the missing polyfill for `json_last_error()` - see #27799

This includes deprecating the `_wp_json_prepare_data()` function which was only needed for PHP 5.2-5.3.


== **Unit tests**

As these functions are used throughout core, removing them can be considered sufficiently unit tested when all the WP Core unit tests pass, and they still do: https://travis-ci.com/WordPress/wordpress-develop/builds/119072132


== **Other**
* I've tried to be comprehensive with this ticket and have searched the codebase for any and all relevant keywords and reviewed all the related code. All the same, as there were quite a lot of different bits and pieces involved in this, I will not guarantee that nothing remains, though I'm fairly confident about the completeness of this patch.
* The patch includes removing the `wp-includes/class-json.php` from the PHPCS exclusions list.

== **Related tickets**
* This ticket is related to #47698 which addresses the other polyfills which can be removed.
* This ticket is related to #27799, #30139.


/cc @pento"	task (blessed)	closed	normal	5.3	General	5.3	normal	fixed	has-patch has-unit-tests i18n-change has-dev-note commit dev-reviewed		coding-standards