Allow computed data to configure special Eleventy Data properties (like pagination) (👍12)

[romaricpascal]

Describe the bug
I'm trying to paginate some data that's returned by an eleventyComputed property. Eleventy breaks announcing it cannot find the property used for the pagination:

Could not resolve pagination key in template data: supportedLocales

To Reproduce

The computed-properties-pagination branch of this repository contains a reduced test case. The test.liquid template tries to paginate over the supportedLocales key defined in data/eleventyComputed. Run npx @11ty/eleventy to get the exception.

If there's a non-computed property with the same name, it will get used for the pagination. You can witness the behaviour using the previous commit on the branch. It contains a property with the same key defined in data/supportedLocales. The test.liquid template does paginate, but does it over the "static" properties not the computed ones.

Expected behavior

I'd have expected the computed property to be used for pagination in both cases, overriding the static ones when they are defined.

Environment:

• OS and Version: Ubuntu 18.04
• Eleventy Version: Using the 11ty/eleventy#9109e76 in package.json.

Additional context
Add any other context about the problem here.

[romaricpascal]

^_^ Computed properties are actually coming to Eleventy: https://www.11ty.dev/docs/data-computed/. The feature is on master so I was trying it out early.

[zachleat]

This docs page is extremely relevant to this discussion: https://www.11ty.dev/docs/advanced-order/

Hmm, let me ponder this one.

[zachleat]

We could move this up in the order of operations but that would have a lot more undesirable implications, specifically I think it would create a circular dependency on computed permalinks (and you wouldn’t be able to access collections in computed functions). This might just be a out of the box limitation of the feature.

Hmm.

At the very least we should throw an error when computed data overrides something used as a pagination key.

[zachleat]

Alright, after some consideration I do think this would be a worthwhile feature but will be a Version 2 iteration of the feature. Note that the docs do currently say “At the end of the Data Cascade.”

I’m going to modify this issue and put it into the enhancement queue.

There are a bunch of special data props in Eleventy that we could use this feature to transform and each of them will require a special case in the order of operations.

e.g.:

collections
page
pagination
permalink
date
dynamicPermalink
layout
tags
templateEngineOverride
eleventyExcludeFromCollections

(via https://www.11ty.dev/docs/data-configuration/)

[zachleat]

In the mean time use the before callback to transform pagination data.

https://www.11ty.dev/docs/pagination/#the-before-callback

[romaricpascal]

Hadn't thought of the before as the latest way for computing data before pagination, thanks for pointing it up. That said, the approach has two drawbacks:

• it needs an actual property for pagination to exist. You can always set a _forComputedPagination dummy in the data so that's not really a blocker.
• the data available inside the before is pretty limited, you only have access to array that's paginated. I'm assuming it's not really intended to fetch data from somewhere else.

All in all, I think I'm not going the right way about those supported locales, so I'll have a rethink about how I use things. Thanks again for the pointers though.

Regarding computing Eleventy special data props, I agree that could be super handy to give more flexibility.

[dz4k]

I would really appreciate this feature — it would mean I could set date from git logs, as I attempted here.

[zachleat]

#4141 was a request specific to eleventyComputed.tags

#1225 was a request for tags

[zachleat]

Cross link to #3882 for eleventyComputed.eleventyExcludeFromCollections