[Twig] add ExposeInTemplate attribute

[kbond]

Q	A
Bug fix?	no
New feature?	yes
Tickets	n/a
License	MIT

#232 made all of a component's public properties available directly (without the this.) in it's template. This adds an ExposeInTemplate attribute to make non-public properties available in this way.

Example:

use Symfony\UX\TwigComponent\Attribute\ExposeInTemplate;

#[AsTwigComponent('with_exposed_variables')]
final class WithExposedVariables
{
    #[ExposeInTemplate]
    private string $prop1; // available as `{{ prop1 }}`

    #[ExposeInTemplate('customProp')]
    private string $prop2; // available as `{{ customProp }}`

    #[ExposeInTemplate(name: 'ico', getter: 'fetchIcon')]
    private string $icon = 'ico-warning'; // available as `{{ ico }}` in the template using `fetchIcon()` as the getter

    /**
     * Required to access $prop1
     */
    public function getProp1(): string
    {
        return $this->prop1;
    }

    /**
     * Required to access $prop1
     */
    public function getProp2(): string
    {
        return $this->prop2;
    }

    /**
     * Required to access $this->icon
     */
    public function fetchIcon(): string
    {
        return $this->icon;
    }
}

TODO:

• use to expose form in ComponentWithFormTrait (requires [Live] Re-extracting form data after submit #254)

[weaverryan]

❤️

[kbond]

What do you think about making this a property-only attribute? Then for methods, we'll recommend either using this. or computed. (from #266)? I think this could help with documentation.

For making form available on ComponentWithFormTrait, I'm thinking we could use this syntax:

trait ComponentWithFormTrait
{
    #[ExposeInTemplate(name: 'form', getter: 'getForm')]
    private ?FormView $formView = null;

    // ...
}

We wouldn't have to rename $formView. The getter attribute argument wouldn't make sense for methods.

[weaverryan]

What do you think about making this a property-only attribute? Then for methods, we'll recommend either using this. or computed. (from #266)? I think this could help with documentation

Hmm, ok. Let's do this. It doesn't prevent us from adding this later by popular demand, so I don't see any risk. 👍

[kbond]

I believe this to be ready.

[weaverryan]

Thank you Kevin - looks awesome!