Shallow git clone

[stsewd]

Close #1888

Tested this locally with a couple of projects, and I didn't find any problems. I also experiment with this outside rtd. The only downside I can see is people using an extension that needs to read the git history. So, this still needs a decision:

1. Merge as it is
2. Add a feature flag and test some projects before
3. Make this a project option, so users can enable/disable it (we can have this on by default)

[codecov]

Codecov Report

Merging #4939 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4939      +/-   ##
==========================================
+ Coverage   76.81%   76.81%   +<.01%     
==========================================
  Files         158      158              
  Lines       10092    10093       +1     
  Branches     1270     1270              
==========================================
+ Hits         7752     7753       +1     
  Misses       1998     1998              
  Partials      342      342

Impacted Files	Coverage Δ
readthedocs/vcs_support/backends/git.py	80.95% <100%> (+0.11%)	⬆️

[ericholscher]

I do wonder if using a higher depth is a bit better. I mentioned back here that travis uses depth=50, to better support extensions that read history, etc.

I think this is a great idea though. I'd be happy to either feature flag it, or just ship it and see what happens :)

[stsewd]

I'm fine with 50 as depth, and skip feature flag, but I wonder if those extensions really exist p: I'll try to search tomorrow.

[stsewd]

I just found https://github.com/OddBloke/sphinx-git and https://github.com/bitprophet/releases, not sure if some use those extensions to generate a full changelog, if not, looks like 50 as depth is good enough

[humitos]

This is a really good change and will save a lot of data (and size) in our builders.

I don't think that this will break, but I'm not sure though. If you already tested it with different types of projects (small and big ones) I suppose we can ship it as is and see what happen with the rest.

[humitos]

I know that git is the most used here, but what about the other VCS? Do we want to implement a similar approach with them?

[ericholscher]

I think we should focus on git. It's definitely an 80/20 (or more) situation, so it gives us the most benefit.

[stsewd]

I tested this with projects that have a lot of versions, but I'll test this again because I want to be sure that this works with #4433

[stsewd]

Tested this with master, still works

[ericholscher]

I wonder if we can make this a default depth, but allow it to be user configurable, so that we have an answer if someone needs more history? We can't have this be a YAML option because we don't have the code on disk yet. I think we can ship this with what we have, but I do imagine we'll need a bit more configurability with it over time.

[humitos]

We can't have this be a YAML option because we don't have the code on disk yet. I think we can ship this with what we have, but I do imagine we'll need a bit more configurability with it over time.

To solve this we can:

1. make it a db option, or
2. implement a feature flag (but it's not possible to set by the user, though)

Although, I don't think we will have any problem in the near future, at least.

[stsewd]

We can make this a web option, something like having all the history or just 50 commits

[humitos]

Considering that we are using shallow clone now, shouldn't we use also --shallow-submodules?

   --depth <depth>
      Create a shallow clone with a history truncated to the specified number of commits. Implies --single-branch unless --no-single-branch is given to fetch the histories near the
      tips of all branches. If you want to clone submodules shallowly, also pass --shallow-submodules.

[stsewd]

That only works when we are cloning the repo and the submodules at the same time, but we don't do that anymore. As the submodules update is separated, I found that we need to update the subdmodules' config to archive this https://stackoverflow.com/questions/2144406/how-to-make-shallow-git-submodules but that looks a little hacky, not sure