Remove additional call to `WP_Theme_JSON::_construct`

[kt-12]

Trac ticket: Trac 61112 Corresponding Guttenberg PR - https://github.com/WordPress/gutenberg/pull/61262

This was found while analysing https://core.trac.wordpress.org/ticket/59600, but it relates mostly https://core.trac.wordpress.org/ticket/57789

In this PR we are trying to avoid second call to new WP_Theme_JSON( $theme_json_data ); as the data can be obtained from WP_Theme_JSON_data class using just a line above by introducing a new public method. At the micro level call to WP_Theme_JSON constructor is expensive.

Interestingly, I can see this change also improved static calls. I wasn't expecting that as in my opinion static lines are only executed once, however, this has challenged my view about static calls and might be we need to be mindful of the performance even while using static.

The execution time of the wp_get_theme_data_custom_templates function on the home page of TT4 was evaluated. Each page had two calls to the function. The second call was static cached so it was significantly lower than the time for the first call.

function wp_get_theme_data_custom_templates() {

	// Capture the start time
	$startTime = microtime(true);
	$data = WP_Theme_JSON_Resolver::get_theme_data( array(), array( 'with_supports' => false ) )->get_custom_templates();	
	// Capture the end time
	$endTime = microtime(true);

	// Calculate the script execution time
	$executionTime = $endTime - $startTime;
	echo "<pre>Execution Time of `wp_get_theme_data_custom_templates`: " . $executionTime . " seconds.</pre>";

	return $data;
}

The performance improvement was as noted below: Before PR

Description	Execution Time (seconds)
Run 1
Execution Time of wp_get_theme_data_custom_templates	0.0033679008483887
Execution Time of wp_get_theme_data_custom_templates	0.00087404251098633
Run 2
Execution Time of wp_get_theme_data_custom_templates	0.003180980682373
Execution Time of wp_get_theme_data_custom_templates	0.00077509880065918
Run 3
Execution Time of wp_get_theme_data_custom_templates	0.0039951801300049
Execution Time of wp_get_theme_data_custom_templates	0.00078392028808594
Run 4
Execution Time of wp_get_theme_data_custom_templates	0.0032379627227783
Execution Time of wp_get_theme_data_custom_templates	0.00077700614929199
Run 5
Execution Time of wp_get_theme_data_custom_templates	0.003154993057251
Execution Time of wp_get_theme_data_custom_templates	0.00075793266296387
Run 6
Execution Time of wp_get_theme_data_custom_templates	0.0032570362091064
Execution Time of wp_get_theme_data_custom_templates	0.00075292587280273

Mean of first call: 0.003366 Mean of static call: 0.000787

After PR

Description	Execution Time (seconds)
Run 1
Execution Time of wp_get_theme_data_custom_templates	0.0030369758605957
Execution Time of wp_get_theme_data_custom_templates	0.0004730224609375
Run 2
Execution Time of wp_get_theme_data_custom_templates	0.0031139850616455
Execution Time of wp_get_theme_data_custom_templates	0.00047683715820312
Run 3
Execution Time of wp_get_theme_data_custom_templates	0.002918004989624
Execution Time of wp_get_theme_data_custom_templates	0.00047898292541504
Run 4
Execution Time of wp_get_theme_data_custom_templates	0.0026509761810303
Execution Time of wp_get_theme_data_custom_templates	0.00044488906860352
Run 5
Execution Time of wp_get_theme_data_custom_templates	0.0027339458465576
Execution Time of wp_get_theme_data_custom_templates	0.00045418739318848
Run 6
Execution Time of wp_get_theme_data_custom_templates	0.0029489994049072
Execution Time of wp_get_theme_data_custom_templates	0.00049400329589844

Mean of first call: 0.002900 Mean of static call: 0.000470

---

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[kt-12]

@joemcgill With the latest changes we are getting a consistent 2.5% improvement without breaking anything.

Performance Metric	Trunk	PR	Improvement (%)
Response Time (median)	387.75	379.09	2.23%
wp-before-template (median)	151.2	145.18	3.98%
wp-before-template-db-queries (median)	0	0	0

[oandregal]

Oh, by the way. It'd be nice if this change would have been done first in the Gutenberg codebase. The value that provides is immense to all of us, including easier synchronization and quick feedback from Gutenberg users if we've missed something. I have nothing against merging it in wordpress-develop first, though I'd kindly ask that the authors port the same PR to Gutenberg. Until we figure out something better, this is what we collectively have and need to care for.

[kt-12]

Oh, by the way. It'd be nice if this change would have been done first in the Gutenberg codebase. The value that provides is immense to all of us, including easier synchronization and quick feedback from Gutenberg users if we've missed something. I have nothing against merging it in wordpress-develop first, though I'd kindly ask that the authors port the same PR to Gutenberg. Until we figure out something better, this is what we collectively have and need to care for.

Thank you @oandregal for your feedback. We clearly understand your feedback about Gutenberg first approach, hence we have already created a PR for Gutenberg - https://github.com/WordPress/gutenberg/pull/61262 . Once it's tested and approved on Gutenberg we can then plan to merge it for the core.

[oandregal]

https://github.com/WordPress/gutenberg/pull/61262

Thank you so much 🙏 I approved the Gutenberg PR.

By reviewing the Gutenberg PR I noticed that the core code is missing a check: see https://github.com/WordPress/wordpress-develop/pull/6271#discussion_r1589940324 and https://github.com/WordPress/gutenberg/pull/61262/files#r1589940214. I don't know why they have differed but that check is important and we should consolidate both codebases.

[joemcgill]

Merged in https://core.trac.wordpress.org/changeset/58185.