Allow arrow functions everywhere

[fabpot]

Closes #3192
Closes #3402

Arrow functions are now supported for all Twig callables (filters, functions, and tests), macro arguments, and method call arguments.

Arrow functions can also be stored in variables.

[fabpot]

Rebased

[Lorenzschaef]

I updated twig for this feature. However, I found that there is one piece missing, to what I was actually looking for. I can store an arrow function in a variable and pass it around, but I can't call it.

My use case:

I have a reusable component/partial, that displays a list of documents as links. Depending on the context, I want the link's URL to be different, so I need to pass a function that generates the link for each item.

What I would expect to work:

<a href="{{ buildUrl(document) }}">

My workaround that does work:

<a href="{{ [document]|map(buildUrl)|first }}>

Are there any plans to support this?

[stof]

The way to call it (in 3.17.1 and newer) is buildUrl.__invoke(document)

Twig does not support using buildUrl(document) as this would be ambiguous whether buildUrl refers to a Twig function or a Twig variable (forcing to remove all validation of function existence from the compile time of templates)

[Lorenzschaef]

Ok, it makes sense to not allow the normal function call syntax then. But isn't the fact that arrow functions have an __invoke() mehtod an (undocumented) implementation detail? I wouldn't really feel comfortable relying on that in my code. I think an invoke filter would be a good solution to this.

[fabpot]

Ok, it makes sense to not allow the normal function call syntax then. But isn't the fact that arrow functions have an __invoke() mehtod an (undocumented) implementation detail? I wouldn't really feel comfortable relying on that in my code. I think an invoke filter would be a good solution to this.

Having a dedicated filter makes sense to me. Would you like to work on this @Lorenzschaef ?

[Lorenzschaef]

@fabpot I can do that, adding the filter shouldn't be hard.