WebP Support

[edmenendez]

I'm opening this issue so that we can keep track of requirements and how support for WebP should be implemented. I'm hoping core contributors would chip in with advise on what areas of the system to look at and minimum features required for this.

Something that is needed is for this PR to be released in Willow: wagtail/Willow#70

Wagtail then needs to be tested against that new version of Willow to make sure it works. Additionally, there are places in the code that make some assumptions about image type that need to be fixed. i.e. https://github.com/wagtail/wagtail/blob/master/wagtail/images/models.py#L401 (thanks @gasman for pointing that out).

I would like to contribute to this feature if there's support within the community for it.

[frmdstryr]

👍 Changes I made to support this: frmdstryr/wagtail@master...frmdstryr:db4271e350a8e54df05bf0b9b0fb436ec060211f (didn't update tests). It allows uploading webp but converts them to png as some browsers don't display webp images.

Also django's ImageField currently has an error due to this issue django/django#10331. The fix is only coming in 2.2 even though it was applied last year.

[onno-timmerman]

I see that this was not added in latest wagtail release? Any reason why wepb is not yet supported?

[gasman]

Completed in #5249 / #5629.