Use canonicalUrl filter in Atom feed

[frankieroberto]

Switching to using the custom canonicalUrl filter defined in this plugin rather than the absoluteUrl filter defined in the eleventy-plugin-rss plugin, so the URLs will include any pathPrefix defined in the Eleventy config.

This is because, I think, the two filters work in subtly different ways:

absoluteUrl resolves a path with a base url, which means that:

'/path/test' | absoluteUrl('https://example.test/prefix') returns https://example.test/path/test - as the initial / in the path indicates a root-relative url.

canonicalUrl appends the paths together, which means that:

'/path/test' | canonicalUrl('https://example.test/prefix/') returns https://example.test/prefix/path/test

An alternative solution would be to use the url filter from Eleventy or the HTML base plugin included with Eleventy 2.0+ - however that one still wouldn't work on the Atom feed as it only transforms links in HTML automatically, and so we’d have to use the htmlBaseUrl filter instead. 🤯

[frankieroberto]

This was all pretty confusing. Perhaps long-term we should aim to remove the canonicalUrl custom filter and use one of the filters built in to Eleventy - but those are currently a bit confused, with many ways to do the same thing.

I think my ideal would be for item.url to return the full URL in all contexts (including any pathPrefix), with no need for any filters. Then if you didn't want a full URL, item.path could be exposed instead?

[paulrobertlloyd]

Before merging, do you want to try using the url filter in the Atom feed? It should work… though given the continued presence of canonicalUrl, maybe it won’t. (I agree, it’s all a bit of a mess; another area of 11ty which is a mess of unexpected behaviour).

[paulrobertlloyd]

Oh wait! I think I know why you can’t! url almost gives you the destined outcome, but doesn’t return a full URL:

{{ "/path/to/file" | url }}
{# returns "/pathPrefix/path/to/file" #}

However, Atom feeds and other places require a fully resolved URL. That’s why I added canonicalUrl:

{{ "/path/to/file" | canonicalUrl }}
{# returns "https://website.example/pathPrefix/path/to/file" #}

Might want to double-check that is true, but from memory that’s what’s going on here.

[frankieroberto]

@paulrobertlloyd yes, it's all very confusing!

As I understand it, url filter correctly adds the pathPrefix to item.url but doesn't include the full domain name. For that, you then need to pass it to another filter.

So, I think there’s (at least) 3 different ways to do this (tested all these locally):

1. {{ item.url | url | absoluteUrl(options.url) }} - this uses the absoluteUrl filter from the RSS plugin and is what the Eleventy docs for the RSS plugin suggests (but that doesn't support the pathPrefix.

2. ``{{ item.url | htmlBaseUrl(options.url) }} - this uses the [htmlBaseUrl`](https://www.11ty.dev/docs/plugins/html-base/) filter.

3. {{ item.url | canonicalUrl }} - uses our custom canonicalUrl filter.

The other thing I’ve realised is that canonicalUrl ignores the pathPrefix setting altogether, but still works if you add the path prefix to the url setting of this Eleventy plugin. So you end up needing to set it in two places:

eleventyConfig.addPlugin(govukEleventyPlugin, {
  url: 'https://www.example.com/my-prefix/'
})

return {
  pathPrefix: '/my-prefix'
}

I think for consistency we should stick with canonicalUrl for now, but perhaps reconsider in future if any of this gets simpler within Eleventy itself?

🤯

[paulrobertlloyd]

Yeah, let’s merge for now and review the use of this filter when Eleventy 3.0.0 comes out; I suspect there might be a lot of things we’ll do a bit differently 🤞