Elements: check value and whitelist before building style nodes

[ramonjd]

Core patch, just in case:

• WP_Theme_JSON Elements: check value and whitelist before building style nodes wordpress-develop#3138

What?

In WP_Theme_JSON::get_style_nodes()

• Check for elements values in theme.json before creating a node
• Check for element name in the whitelist before creating a node

Context: #41160 (comment)

Why?

If an element does not exist in the static::ELEMENTS whitelist, PHP will complain about Notice: Undefined index.

This won't fix the current notice in core, but is a preparatory patch for the 6.1 migration.

Testing Instructions

Check that the tests pass.

To check manually that things are still working, here's some test theme.json

{
	"version": 2,
	"settings": {
		"appearanceTools": true,
		"layout": {
			"contentSize": "840px",
			"wideSize": "1100px"
		}
	},
	"styles": {
		"elements": {
			"button": {
				"color": {
					"background": "green"
				}
			}
		}
	}
}

Using this JSON, your buttons should have a green background.

[Mamaduka]

This will produce an Undefined index in PHP 5.6 - https://3v4l.org/vqKpS#v5.6.40, and we cannot use isset() since it will result in a fatal error.

So let's use array_key_exists, similar to #42567.

[ramonjd]

Thanks @Mamaduka

Just checking, do you mean the isset( $theme_json['styles']['elements'][ $element ] ) or empty( static::ELEMENTS[ $element ] )?

Or isn't empty okay with constants either?

I'll update to

if ( ! isset( $theme_json['styles']['elements'][ $element ] ) || ! array_key_exists( $element, static::ELEMENTS ) ) {

[Mamaduka]

Sorry for not being clear; it's still early morning for me ☕

I mean - empty( static::ELEMENTS[ $element ] )

The isset and empty don't work as you expect with class constants in PHP 5.6.

[ramonjd]

Ah great. I knew about isset, but TIL about empty. Thanks a lot for the nudge.

Updated.

[Mamaduka]

Thanks for the quick follow-up.

[mcsf]

Thanks for the quick fix :)

[scruffian]

Thanks for taking care of this.

[oandregal]

Hey, while working on #46579 I realized this PR was not backported to WordPress 6.1. When we land that PR and then backport to WordPress 6.2 everything will be fine, but I wanted to raise in case you think this should be ported for a potential WordPress 6.1.X release.

[ramonjd]

Thanks for the heads up @oandregal
This one must have fallen through the net. I'll make note of it.