Add support for as in Render and Include tags

[shopmike]

This is to support a new syntax that allows with and for to be aliased to something other than the template name.

Include now supports as

Example

{% include 'product_alias' with products[0] as product %}

Usage inside product_alias would be

{{ product.title }}

Render now supports with, for and as

Render now supports with and for with a major difference being that render generates a new subcontext for each loop in for. This means each iteration of for cannot impact others, this will allow loops to be async in the future for performance improvements.

@Shopify/guardians-of-the-liquid @samdoiron @Thibaut

[Thibaut]

Why #{VariableSignature}+ and not just #{VariableSignature}? (if we expect only one)

[shopmike]

VariableSignature = /\(?[\w\-\.\[\]]\)?/ only matches characters so we expect many

[shopmike]

I'm actually thinking now I should change this to VariableSegment = /[\w\-]/

[Thibaut]

Protip: variable = Array(variable)

[Thibaut]

That said we could also maybe turn the .each into a method, so that we can avoid making a one-item array and do something like instead:

if variable_is_a?(Array) then variable.each(&:method_name) else method_name(variable)

[shopmike]

This doesn't seem to be fully equivalent variable = Array(variable). I think its treating nil as [] however need it to be [nil] so it loops.

I was originally going down the method path but there are so many params in this scope that would need to pass in context, template_name, output, var, partial

[Thibaut]

Good point. Let's add for that then.

[shopmike]

Not sure on the Rubyist view on this, but just used a lambda to group the functionality, gets around excessive params and needing to create a fake array.

[Thibaut]

Oh actually, could we force quotes around the variable name. Otherwise it reads like you're passing a dynamic name defined by a variable.

[shopmike]

I think it should be the way it is, It's not a string it's forcing you to define the variable you want it to be. Matches up with how other tags are defined

{% render "product" product as product %}
{% for product in products %}
{% assign product = products %}

[shopmike]

For me that syntax suggests these should all be

{% render "product" product as "product" %}
{% for "product" in products %}
{% assign "product" = products %}

[Thibaut]

Hmm but then I would think it sets a variable in the parent context. What do you not like about: {% render "product" with product as "product" %}?

[shopmike]

it's just so out of place, it's the only instance where a variable name would be quoted. For me, anything inside quotes means you can have any character. In this instance, it is introducing a new concept.

[shopmike]

instead of the normal "(.*)" you have a similar but different "([\w-]*)"

[Thibaut]

Ah I see. Good point.