Perform a canonical redirect when paginated states of the front page are not found

[dd32]

As a followup to #45337, [34492], and [47727].

When example.com/ has a static front page assigned and uses <!--nextpage--> accessing non-existing pages uses example.com/page/3/ and Canonical won't kick in.

This is because paged states of the front page use the paged query var, not the page query var.

Should also fix ​https://meta.trac.wordpress.org/ticket/5184 :)

See https://core.trac.wordpress.org/ticket/50163

[SergeyBiryukov]

Thanks for the ticket, I'm working on this as part of #28081 :)

[SergeyBiryukov]

Didn't get a chance to write the tests for this in time for 5.5 RC, moving to 5.6.

[mukesh27]

Adding the refresh keyword for the PR merge conflict.

[audrasjb]

Patch refresh

[audrasjb]

before patch: example.com/page/3 exists

[audrasjb]

After patch: example.com/page/3 redirects to homepage

[audrasjb]

50163.diff refreshes the previous patch. It appears to fix the issue.

[mukesh27]

Patch 50163.diff​ applied fine in trunk version

[SergeyBiryukov]

Thanks for the refresh! This still needs tests though, moving to the next release for now.

[audrasjb]

Just to be sure: do we need unit tests @SergeyBiryukov ?
Because in my testing the suggested patch fixes the issue.

[SergeyBiryukov]

Yes, sorry I was not clear enough :) Any functional changes to the Canonical component should really be accompanied by unit tests, to avoid unexpected regressions like comment:40:ticket:12456.

[audrasjb]

Ok thanks for clarifying. I'll make sure to get those unit tests for the next release as I already saw at least one example of SEO impact of this issue.

[lukecarbis]

Since we're in 5.7 beta 3, let's move this to the next release.

[chaion07]

We reviewed this ticket during a [recent bug-scrub]​https://wordpress.slack.com/archives/C02RQBWTW/p1622579264170500. Pinging @audrasjb for the [unit tests]https://core.trac.wordpress.org/ticket/50163#comment:9. Are these likely to be done before Beta 1 or this should be punted to the Future Releases? Thanks!
Props to @jeffpaul ​https://wordpress.slack.com/archives/C02RQBWTW/p1622579402171400

[hellofromTonya]

Today is 5.8 Beta 1. This one needs tests. Punting to 5.9. But also adding to my tests TODO list. And to ensure I don't forget, @SergeyBiryukov changing ownership to me for the tests.