Re-implement handling Liquid blocks in excerpts

[ashmaroli]

Resolves #7248

This re-implementation should be able to handle multiple Liquid blocks in excerpts.

@djacquel I invite you to test this branch against various valid combinations of Liquid blocks so that we can get rid of this issue for good. Thanks in advance.

@jekyll/core I request this PR to be considered a.s.a.p and be backported to the 3.8-stable series

[mattr-]

Please address the inline comments.

As part of excerpt generator, do we need to be concerned about liquid object tag pairs ({{ and }})?

[mattr-]

The capture for this regular expression isn't 100% correct. A liquid tag of {%highlight%} will lose the last letter, meaning that the capture group will contain highligh instead of highlight

I wrote a quick test case for this on Rubular as well, as an extra example: http://rubular.com/r/umPU5g5PiH

[ashmaroli]

Thank you for catching this @mattr- 🙂

[ashmaroli]

do we need to be concerned about liquid object tag pairs ({{ and }})?

@mattr- No, we shouldn't handle deviation from the formats used by the majority of the users: {{variable}} or {{ variable }}.

[mattr-]

@ashmaroli Sorry, not sure I understood you. Are you saying that since {% and %} tag pairs are the most common, we don't need to handle {{ and }} tag pairs?

[djacquel]

No more error thrown, just the warning. Good job.

[ashmaroli]

Are you saying that since {% and %} tag pairs are the most common, we don't need to handle {{ and }} tag pairs?

@mattr- Not at all..
We are handling only {% and %} for Liquid::Block type tags. i.e. tags that have an opener
(e.g. {% raw %}) and a closer (e.g. {% endraw %}). Regular tags like {% assign %} are not handled.

[ashmaroli]

Oh.. The Utterson Report doesn't look good.. 🙁

ref	build time in seconds
#7250	344.02
master	329.06

[pathawks]

@ashmaroli Correctness wins over performance 👍🏼

[pathawks]

These are all the same warning, not separate messages, correct?

[ashmaroli]

@pathawks Yes. These calls are for the same warning.
I split them out into separate calls so that the messages appear to be formatted on the CLI.

I can't use a heredoc to emulate the formatting because Jekyll's logger squashes all whitespace into a single space char, which causes heredoc messages to simply print as a single line message.

[ghost]

@jekyllbot: merge +bug