SSViewer::chooseTemplate sometimes do the work twice

[lekoala]

Affected Version

4/5

Description

Another finding from the new cache collector in the debugbar for v5.

When calling an include, it's first resolved based on an array of argument, then as a path. Typically, this happens for LeftAndMain_Menu

• First, a call is made passing an array with a bunch of stuff
• Then, another call is made with a path like this ...\silverstripe\subsites\templates\SilverStripe\Admin\LeftAndMain_Menu.ss"

This leads to two cache keys being created for the same entry (one when you give an array, one when you pass a file path)

silverstripe-framework/src/View/ThemeResourceLoader.php

Lines 192 to 196 in 158d51a

	// Look for a cached result for this data set
	$cacheKey = md5(json_encode($template) . json_encode($themes));
	if ($this->getCache()->has($cacheKey)) {
	return $this->getCache()->get($cacheKey);
	}

Setting the cache key itself is a good idea to avoid file_exists checks, but it feels like doing the work twice. Once resolved from the array, you know the file_exists, and it could be cached in a static array instead and avoid cache checks completely.

Proposal

So this is a quicky and dirty proposal, but it gives an idea

public static function chooseTemplate($templates)
{
    static $arr = [];
    if (is_string($templates) && isset($arr[$templates])) {
        return $templates;
    }
    $resolved = ThemeResourceLoader::inst()->findTemplate($templates, self::get_themes());
    $arr[$resolved] = true;
    return $resolved;
}

When a file is resolved, it's stored a in a static array. If we ask for this file again, simply return the file path directly without any cache checks.
If the team is interested, i'm happy to work on a PR.

It's by no means a big issue, but it saves 5 cache calls on a typical admin page for example, but it's probably more if you have lots of includes

[lekoala]

side note: file_exists is also cached at php level directly, so maybe it's even simpler to simply return early and use file_exists checks when given a file path ending with .ss