Detects if master branch has diverged and warn to pull new commits

[MRinalducci]

Hi Luke,

I've worked on implementing a warning in the comment if master has changed like as I suggested in issue #804.

There is an example at MRinalducci/atlantis-example#1 (comment).
It adds message: ":warning: Master branch is ahead, it is recommended to pull new commits first."

Can you please give me your inputs about this PR?
I think about to implement a "pull/merge" command. What do you think?

[codecov]

Codecov Report

Merging #815 into master will decrease coverage by 0.01%.
The diff coverage is 76.66%.

@@            Coverage Diff             @@
##           master     #815      +/-   ##
==========================================
- Coverage   71.83%   71.82%   -0.02%     
==========================================
  Files          65       65              
  Lines        5213     5203      -10     
==========================================
- Hits         3745     3737       -8     
+ Misses       1183     1181       -2     
  Partials      285      285

Impacted Files	Coverage Δ
server/events/markdown_renderer.go	92.5% <ø> (ø)	⬆️
server/events/models/models.go	75% <ø> (ø)	⬆️
server/events/project_command_runner.go	74.33% <100%> (+0.22%)	⬆️
server/events/project_command_builder.go	83.01% <100%> (+0.89%)	⬆️
server/events/working_dir.go	75% <73.07%> (ø)	⬆️
server/events/yaml/parser_validator.go	96.66% <0%> (-0.15%)	⬇️

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[lkysow]

Nice work, I think this is a good approach. You need to add tests for both working_dir and markdown_renderer that exercise the new functionality.

[MRinalducci]

Hi,
Thank you for your review and comment.
Ok no problem, I'll add tests for both files.

[MRinalducci]

Hi @lkysow,
As you asked I added the tests for working_dir and markdown_renderer.
I'm coming just too late for getting in the current release.

[lkysow]

Does this work? I'm seeing that the status is just looking at the remote tracking branch which isn't master but the same branch:

$ git status
On branch autoplan
Your branch is up to date with 'origin/autoplan'.

nothing to commit, working tree clean

Even when master is ahead.

[lkysow]

Shouldn't we skip this section if any of the above commands fail? Maybe pull it into its own function so you can return early.

[MRinalducci]

I did it like this because I don't want to impact the clone function if for any reason it cannot detected that master branch has diverged as it displays only a warning in the comment of the plan.

[MRinalducci]

Yes this is working, did you tried with argument --checkout-strategy=merge ?

I got this:

$ git status --untracked-files=no
On branch master
Your branch and 'origin/master' have diverged,
and have 2 and 1 different commits each, respectively.
  (use "git pull" to merge the remote branch into yours)

[lkysow]

Closed by #867 (I took all your commits and made some small changes, awesome work! 🎉 )