Add config variable to avoid canonical redirect

[xavivars]

Description

This PR introduces a config variable that allows you to disable redirect when a page loads, in case the paths are different when generated and when displayed.

This used together with https://github.com/wardpeet/gatsby-plugin-static-site allows to use gatsby as a static page generator instead of a static site generator

Related Issues

This PR is basically the same one as #11914 and fixes #4337

[KyleAMathews]

Generally speaking we don't add config options. Is there another way we can solve this?

[xavivars]

I'd love to have another way to do this, but I can't think of another way to break this if

gatsby/packages/gatsby/cache-dir/production-app.js

Line 77 in 56950e6

!__DISABLE_LOAD_TIME_CANONICAL_CHECK_REDIRECT__ &&

Up until 2.9, there was a workaround, that involved changing what is currently window.pagePath to browser's location hooking into clientEntry but that stopped working due to the new per-page page-data.json relying on that window.pagePath.

I don't now if creating a new hook at that point in the code is preferable to a config variable...

[xavivars]

Maybe being able to override here the value of browserLoc to not to use the real browser window.location could also work, but I have no idea on how that could be done...

gatsby/packages/gatsby/cache-dir/production-app.js

Line 65 in 0fa5955

const { pagePath, location: browserLoc } = window

[xavivars]

@KyleAMathews, this PR takes a much simpler approach, and enables the same use case

#15180

Do you think the approach is better?

[wardpeet]

Hey @xavivar, thank you for opening this pull request!

Unfortunately, the proposed change is not going to be merged. This is a fairly unusual usecase, and while we'd love to support every usecase for everyone we don't have the capacity to do that right now. It may seem like a small change but any time we expose apis publicly like this it means we're committed to supporting them, which can lead to problems when we change them later on.

Thanks again, and we look forward to seeing more PRs from you in the future! 💪💜