Fix: respect parameter order when using "for ... reversed"

[stedman]

With regards to the for tag's reversed parameter, I found the current behavior of reversing a collection after all the other parameters execute a bit unexpected (and not very useful).

Given {% for i in (1..8) reversed limit: 4 %}{{ i }}{% endfor %}, I would expect the params are executed from left to right. In other words, the collection is reversed first and then limited to four items with an output of 8765.

Instead I get 4321, which is what I would expect with {% for i in (1..8) limit: 4 reversed %}{{ i }}{% endfor %} where the collection is limited to the first four items before reversing.

My use case for this is reversing a large collection of blog posts (so they are listed as most recent first) and then sizing those results down to five posts for the home page.

This proposed change will impact existing code that uses reversed with additional params. If this PR seems too risky, perhaps adding a new parameter (flipped?) with the proposed functionality would do the trick.

[harttle]

I'm afraid it's not conformant which means it'll break Jekyll sites and Shopify templates, though I absolutely like this point.

Try file an issue on https://github.com/Shopify/liquid instead.

[stedman]

@harttle thanks for the quick feedback! It looks like this was proposed 5+ years ago but fizzled out.

I added my voice to the issue with yet another suggestion to extend reversed with an optional value to achieve the same goal: {% for i in (1..8) reversed:"first" limit:4 %} outputs 8765. We'll see what happens.

[harttle]

Added orderedFilterParameters option to enable this feature and changed your last test case

{% for i in (1..8) offset:2 reversed limit:3 %}{{ i }}{% endfor %}

expected value from 543 to 876 because reversed should happen before limit.

And there's a strange behavior, which I consider it as a bug, in Shopify liquid that

{% for i in (1..8) offset:2 reversed %}{{ i }}{% endfor %}

yields 345678, but

{% for i in (1..8) reversed offset:2 %}{{ i }}{% endfor %}

yields 876543. We'll not follow this behavior even if orderedFilterParameters is set to false.