[LiveComponent] Undefined array key "placeholder" after upgrading to 2.22.x

[maciazek]

Hello,

recently after upgrading symfony/ux-live-components to 2.22.x I've encountered this exception:

An exception has been thrown during the rendering of a template ("Warning: Undefined array key "placeholder"").

Here's the reproducer: https://github.com/maciazek/symfony-ux-live-components-choices-reproducer

I have a custom DatalistType form field, which extends TextType to add HTML datalist into it. Inside DatalistType I'm using 'choices' option to add choices to datalist.
https://github.com/maciazek/symfony-ux-live-components-choices-reproducer/blob/master/src/Form/DatalistType.php#L11-L29
https://github.com/maciazek/symfony-ux-live-components-choices-reproducer/blob/master/templates/form/custom_types.html.twig

I have a form inside live component which is using DatalistType as a child field.
https://github.com/maciazek/symfony-ux-live-components-choices-reproducer/blob/ebe9ff77a7181ed6e0ca4dd5fca7483f38e8ed94/src/Form/ExampleType.php#L9-L30
https://github.com/maciazek/symfony-ux-live-components-choices-reproducer/blob/ebe9ff77a7181ed6e0ca4dd5fca7483f38e8ed94/src/Twig/Components/ExampleForm.php#L13-L23

Everything worked well until updating symfony/ux-live-components to 2.22.x - then I've encountered previously mentioned error.

After some investigation I've found that problem is caused by recent change in ComponentWithFormTrait:
https://github.com/symfony/ux-live-component/blob/5adf780aac0ccbd5cb1dddea683db9aa99b91d4a/src/ComponentWithFormTrait.php#L264-L271

I have 'choices' option in my DatalistType, but it's extending TextType which, as I guess, has no default values for placeholder, multiple and expanded options so they're missing in vars array.

Possible solutions:

1. I can rename option 'choices' to something different, but I still haven't found a better name :)
2. I can set default values for placeholder, multiple and expanded and assign them to vars inside buildView function in my DatalistType - that's my temporary workaround;
3. Maybe these recently added vars tests could be null-coalesced or array_key_exists-ed in ComponentWithFormTrait?

Thank you for your great work on the whole UX ecosystem!

[smnandre]

Indeed, there should be a

&& \array_key_exists('placeholder', $child->vars)

before accessing the value.

Would you be ready to open a PR ?