Better UX when git checkout to a not existing branch/tag

[stsewd]

Sometimes we can end in a case where the user deletes a version in their repo and want to build that version in rtd. When this happens, the user needs to build a different available version.

Because of the order of the build process, a wipe isn't enough to solve this

• RTD will clone or update the repo as a first step
• Then, rtd will fetch the new versions (and deletions)
• RTD will checkout to the version that is going to build
  • RTD will fail here because executes git checkout latest
  • latest doesn't exist on the repo at the time (we updated the repo!)
• RTD will sync the versions with the data from the repo
  • This step never happens it the previous fails

This currently affects branches only and should affect tags after #4258 is solved

Raised in #3913 (comment)

[stsewd]

A solution can be: change the build process order

• clone or update the repo as a first step
• fetch the new versions (and deletions)
• sync the versions with the data from the repo
• checkout to the version that is going to build

But I'm not sure about the consequences of this change

https://github.com/rtfd/readthedocs.org/blob/9a4c45932cf6f1cf4f878e06e27d281f2cf24736/readthedocs/projects/tasks.py#L145-L147

[humitos]

I suppose that this issue will be solved by #4876, right?

[stsewd]

Yup, I forgot to linked it

[stsewd]

Actually no, this one will fix this #4901