Addition to strict mode: fail on nonexistent variable dereferencing

[parkr]

In jekyll/jekyll#3008, @gjtorikian wrote of one woe of using Liquid: it swallows references to non-existent variables.

It would be amazing, when error_mode = :strict, to throw an error in this case. It would really help Liquid scale out to larger teams, I think, and would help surface annoying rip-your-hair-out issues that Liquid allows for today.

What do you think?

[fw42]

Hmm. not sure how easy that is. error_mode strict is a parser option (not a rendering option), but missing variables can often only be determined during runtime (think conditional uses of the include tag).

@pushrax what do you think?

[nickpearson]

Something like this may warrant an additional setting, like fail_on_missing_reference = true or something.

I often depend on being able to reference a variable that may or may not exist, defaulting to some other value if it doesn't. For example: {{ may_not_exist | default: definitely_exists }}

I think this is similar to how you can safely reference nonexistent object properties, like {{ a.b.c.d.e }} even if a == {}.

I can definitely see how existential enforcement would be helpful in some cases, but I wanted to point out a couple where it would limit the ways in which Liquid can be used. For that reason, I think it would be good to make this configurable independent of the error_mode.

[arp242]

FYI all, I did some basic work on this, see the commit above. I need to go fix our templates first, but just so that you know it's in the works ;-)

[gjtorikian]

Great! Thank you!

[parkr]

@pushrax what do you think?

☝️

[pushrax]

@Carpetsmoker I added a few comments to your commit, feel free to submit a PR after you take a look at them.

[gjtorikian]

Any updates here? 🙏

[parkr]

It would be nice. Very nice.

[fw42]

@Carpetsmoker: Are you interested in addressing the comments and finishing this? If not, I can take a look myself.

[fw42]

@parkr: Is this something you would want to include in Jekyll 3? If yes, I will take a look soon (since I know you want to release soon). If it can wait, then I will focus on other things for now :-)

[parkr]

Is this something you would want to include in Jekyll 3?

It would be marvelous! We're more lenient in Jekyll 3 with our Liquid version so if it is added to Liquid later, we could turn it on later as well (if it is not automatically enabled).

If you have other, more important things however, don't fret over this one. It's fine if it comes later.

[arp242]

@fw42 I did this for my previous job, which is my, well, no longer my job ;-) I don't mind finishing this as such, but at the moment I'm using my girlfriend's OSX machine, and I don't really want to mess around with Ruby and such (apparently you need homebrew and whatnot, and I've never really used OSX).

So yeah, I'll work on it, but not in the next week orso. Anyone else can of course also work on it if she or he has the inclination to do so ;-)