Adding a SitemapBuildableView to generate a wagtail sitemap.

[NDevox]

This will fix #37.

[loicteixeira]

Hi @NDevox, thank you for your contribution and sorry for the late review.

Unfortunately with Wagtail before 2.2, it fails with the following error AttributeError: 'WSGIRequest' object has no attribute 'site'. Indeed, as you can see here it tries to query the request's site in the view but this behaviour was changed in wagtail/wagtail@a3fe8eb which is included in Wagtail 2.2. It might simply be a matter of duplicating the new get_wagtail_site for versions prior to 2.2. However we might not need to do so as we might drop compatibility with Wagtail prior to 2.2 soon (see #36).

In addition, I didn't run tests for it yet but I suspect it won't be compatible with the multi-site option. As you can see, other views' build path differs whether we use multi sites:

https://github.com/wagtail/wagtail-bakery/blob/0937dde07d1791a3780079a1b6959eb0b9c43d55/src/wagtailbakery/views.py#L65-L69

[Benoss]

I am using part of your pull request as my own SitemapBuildableView works perfectly for my use case. Would be good to get this work with multisite and merged at some point.
The current LTS is 2.3 Dropping support for < 2.3 would make sense. This is also the last Wagtail version to support Django 1.11.

[loicteixeira]

I'm focussing on preparing the Wagtail repository for Hacktoberfest over the next couple weeks, then I'll work towards merging this and fixing other issues which have been reported.

[NDevox]

@loicteixeira Sorry I dropped off on this one!

If we drop support for < 2.3 obviously that makes things simpler. I'll wait for your input on that one.

I've not tested for multisite, I've also not had to use it for wagtail before! I can give that an attempt and see what happens. My thought on this one would be what behaviour would be expected? A class that builds all sitemaps in one go? Would we want to allow sites to be filtered? or demand a specific class instance for each site?

[loicteixeira]

I'll update the test matrix as per #36 this week so you should be able to rebase on that after.

As for the expected behaviour, yes, one class which builds all sitemaps in one go, as does the base view:

https://github.com/wagtail/wagtail-bakery/blob/0937dde07d1791a3780079a1b6959eb0b9c43d55/src/wagtailbakery/views.py#L65-L69

[loicteixeira]

@NDevox I rebased & continued your work on the PR linked above which supersed this one. Thank you for getting this started.