Allow commas to separate for tag attributes

[dylanahsmith]

Problem

There are multiple tags that use Liquid::TagAttributes to scan for attributes, but the only one that has strict parsing is the for tag and that strict parsing doesn't allow commas as separators as we typically use in other tags for tag attributes.

For example, the render tag documentation for passing variables to a snippet demonstrates this with {% render 'filename', variable: value %}. Based on what I see in the dawn theme, it looks like this is our preferred style (e.g. we have {% render 'card-collection', card_collection: block.settings.collection , media_aspect_ratio: section.settings.image_ratio, columns: columns %})

In contrast, trying to use the same style in the for tag (e.g. {% for i in array, limit: 4, offset: 2 %}...{% endfor %}) would be a syntax error in strict parsing mode, requiring only a space to be used as a separate (e.g. {% for i in array limit: 4 offset: 2 %}...{% endfor %}).

Solution

Update Liquid::For#strict_parse to optionally allow commas to separate tag attributes.

Note that the for tag also allows a reversed option to be specified, but it is different from a tag attribute in that it isn't given a value and is expected to precede any tag attributes. Given this, I decided it didn't need to also allow a comma to precede it.