Allow JSON_PRETTY_PRINT to be used without notice on PHP < 5.4

[markjaquith]

JSON_PRETTY_PRINT was introduced in PHP 5.4. If you attempt to use it in PHP < 5.4 as an option passed to json_encode() or wp_json_encode() , you'll get a notice about the undefined constant.

As it is just a human-readable thing and doesn't functionally affect the output of the JSON, we should just define the constant if it’s not defined. That way people can use it without doing a version check, and if PHP supports it, they get pretty output, otherwise, they silently get standard non-pretty output. I don't think we should add other constants, because they do affect the functionality of the output, and so silent failure would be a bad thing.

See also #29435 and #28786 (wp_json_encode() will support the option as well, on PHP versions that can accept the options argument).

[markjaquith]

I added it to compat.php instead of default-constants.php because it’s not our constant — it’s part of our PHP compat layer. But I don't feel strongly about that.

[nacin]

I agree with compat.php.

I'd add "to prevent a notice when used with wp_json_encode().", otherwise my next question would be why we need to have this.

[markjaquith]

In 30075:

Define JSON_PRETTY_PRINT so it can be used with wp_json_encode()

• JSON_PRETTY_PRINT was introduced in PHP 5.4
• Now you can use it with lower PHP versions, without a notice

fixes #30139
see #28786