[TwigComponent] Skip mount hooks on anonymous components when nobody listens to mount events

[Kocal]

Q	A
Bug fix?	no
New feature?	no
Deprecations?	no
Documentation?	no
Issues	-
License	MIT

Every component goes through ComponentFactory::mountFromObject(), which calls preMount(), mount() and postMount(), each checking for listeners and hooks, reads a few ComponentMetadata accessors that go through get(), and fetches the escaper with Environment::getRuntime(). Anonymous components, which UX Toolkit kits are made of, have no hooks and no properties to set, so when nobody listens to PreMountEvent and PostMountEvent, none of that work can change anything. It costs about 0.4 µs per component.

• anonymous components are mounted directly when nobody listens to the mount events; the PreMountEvent listener check is reused by preMount(), so the regular path, taken for instance when LiveComponent is installed, does not check twice

• ComponentMetadata accessors read the configuration directly instead of going through get()

• ComponentFactory keeps the EscaperRuntime instead of fetching it for every component

• standalone benchmark below (300 anonymous components, 100 renders, 4 interleaved runs each, identical output): 293-296 ms before, 274-277 ms after (-6.5%)

• an admin dashboard built with the Shadcn kit, 1,767 components per request: preMount() and postMount() go from 1,767 calls per request to 0; Blackfire (5 samples of 5 requests) goes from 2.48 s to 2.37 s wall time (-4.4%); raw CPU median per request goes from 48.2-50.4 ms to 46.5-49.0 ms (noisy machine, 6 interleaved runs of 60 requests each side)

<?php

// Run from src/TwigComponent: php bench.php
use Symfony\Bundle\FrameworkBundle\FrameworkBundle;
use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Bundle\TwigBundle\TwigBundle;
use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
use Symfony\Component\HttpKernel\Kernel;
use Symfony\UX\TwigComponent\TwigComponentBundle;

require getcwd().'/vendor/autoload.php';

$dir = sys_get_temp_dir().'/ux-twig-component-bench-'.bin2hex(random_bytes(4));
mkdir($dir.'/templates/components', 0777, true);
file_put_contents($dir.'/templates/components/Cell.html.twig', <<<'TWIG'
    {% props variant = 'default' %}
    <td data-variant="{{ variant }}" {{ attributes.defaults({class: 'p-2 align-middle'}) }}>{% block content %}{% endblock %}</td>
    TWIG);
file_put_contents($dir.'/templates/components/Badge.html.twig', <<<'TWIG'
    {% props label %}
    <span {{ attributes.defaults({class: 'badge'}) }}>{{ label }}</span>
    TWIG);
// 25 rows of 6 embedded cells, each holding a self-closing badge: 300 components
file_put_contents($dir.'/templates/table.html.twig', <<<'TWIG'
    {% for row in 1..25 %}<tr>
        {% for col in 1..6 %}<twig:Cell variant="{{ col is odd ? 'odd' : 'even' }}" class="cell-{{ col }}"><twig:Badge label="{{ row }}-{{ col }}" data-row="{{ row }}" /></twig:Cell>{% endfor %}
    </tr>{% endfor %}
    TWIG);

$kernel = new class('prod', false, $dir) extends Kernel {
    use MicroKernelTrait;

    public function __construct(string $environment, bool $debug, private string $dir)
    {
        parent::__construct($environment, $debug);
    }

    public function registerBundles(): iterable
    {
        yield new FrameworkBundle();
        yield new TwigBundle();
        yield new TwigComponentBundle();
    }

    public function getProjectDir(): string
    {
        return $this->dir;
    }

    protected function configureContainer(ContainerConfigurator $container): void
    {
        $container->extension('framework', ['secret' => 'S3CRET', 'test' => true, 'http_method_override' => false]);
        $container->extension('twig_component', ['anonymous_template_directory' => 'components', 'defaults' => []]);
    }
};
$kernel->boot();
$twig = $kernel->getContainer()->get('test.service_container')->get('twig');
$html = $twig->render('table.html.twig');

$times = [];
for ($run = 0; $run < 7; ++$run) {
    $start = hrtime(true);
    for ($i = 0; $i < 100; ++$i) {
        $twig->render('table.html.twig');
    }
    $times[] = (hrtime(true) - $start) / 1e6;
}
sort($times);
printf("100 renders of 300 components: median %.0f ms (min %.0f, max %.0f) | sha1 %s\n", $times[3], $times[0], $times[6], sha1($html));

Blackfire profiles (dashboard page):

• Before: https://app.blackfire.io/envs/5f4f9a62-eaa0-45ee-b7b3-a1b879f550e9/profiles/a28b57f5-dff1-4e21-bd75-bb859a840bf8/graph
• After: https://app.blackfire.io/envs/5f4f9a62-eaa0-45ee-b7b3-a1b879f550e9/profiles/a2ac9218-9141-4b33-9d0c-b5e1f069a01c/graph
• Comparison: https://app.blackfire.io/envs/5f4f9a62-eaa0-45ee-b7b3-a1b879f550e9/profiles/compare/a28b57f5-dff1-4e21-bd75-bb859a840bf8...a2ac9218-9141-4b33-9d0c-b5e1f069a01c/graph

This dashboard is available at https://github.com/Kocal/sf-ux-perfs-twig-components.