Share doctree between builders

[stsewd]

We are reducing build time with this.
And also saving a little of space in the builders.

According to sphinx, we are safe doing this:

the doctrees can be shared between all builders

http://www.sphinx-doc.org/en/master/man/sphinx-build.html#cmdoption-sphinx-build-d

Closes #4363

[stsewd]

Tested this in the local instance inside docker, I don't see much improvements in the time like it did outside (#4363 (comment))

But the obvious improvement is the size.

[agjohnson]

Perhaps this would make sense under a feature flag. I feel like none of us remember why we had to separate the doctree in the first place, I'm guessing we'll find out really quick 🙂

[stsewd]

Sorry but it was bothering me seeing this js kind of indentation p:

[humitos]

Is this change made by pre-commit? If you did it manually, it will be reverted in the next pass otherwise.

[stsewd]

I did it manually, but I run precommit on this file, and it didn't change anything

[stsewd]

@agjohnson feature flag added

[humitos]

The PR looks very simple to me and accurate.

I like the idea of having it under a Feature flag. We need to remember to add the flag and sample some projects after deploying it.

[humitos]

BTW, shouldn't we update this docs https://docs.readthedocs.io/en/latest/guides/feature-flags.html ?

[stsewd]

BTW, shouldn't we update this docs https://docs.readthedocs.io/en/latest/guides/feature-flags.html ?

I don't think so, we are just testing this to then remove it, and this shouldn't affect users at all if what we are doing is ok. So, feature flag will be removed soon if things go well :)

[stsewd]

I'm adding a trello card to keep track of adding this flag to some projects

[ericholscher]

Pretty sure this is going to blow up in production. We can have multiple projects running on the same builder across different versions, which will cause weird race conditions from this I'm 99% sure.

[stsewd]

But the _build/ folder is created for each version, we can only have race conditions if we trigger a build to the same version twice, the same race condition would be seen before this change.

[ericholscher]

Ah right, it must have been another issue then. Guess we'll see in prod as Anthony said.