Re: [PATCH] ci: github action - add check for whitespace errors

[Jeff King <peff@peff.net>]

On Tue, Sep 22, 2020 at 03:17:54PM -0700, Chris Webster wrote:

> On Tue, Sep 22, 2020 at 10:07 AM Jeff King <peff@peff.net> wrote:
> >  - for a linear branch on top of master, using the commit count will
> >    work reliably. But I suspect it would run into problems if there were
> >    ever a merge on a PR (e.g., back-merging from master), where we'd be
> >    subject to how `git log` linearizes the commits. That's not really a
> >    workflow I'd expect people to use with git.git, but it would probably
> >    be easy to make it more robust. Does the PR object provide the "base"
> >    oid, so we could do "git log $base..$head"?
> 
> GitGitGadget PR linting is going to flag merges in the PR and request
> a rebase.  If I understand correctly, that means back-merging is not
> part of the workflow.

Yeah, I would definitely be surprised to see it used with a git PR, but
I didn't realize there was other linting that would actually complain
about it.

> The checkout is limited to improve performance
> and reduce resources.  In the PR object, the base is the branch.  The
> github api would need to be used to get more detailed information.
> The "base" is not really part of the checkout so it can not be
> referenced in the git log command (without doing a larger checkout).

Hmm.

  git clone --shallow-exclude=HEAD --single-branch -b $branch
  git log --check

_almost_ works. The problem is that the shallow graft means that the
bottom commit looks like it introduces every file. We really want to
graft at HEAD^, but the server side only accepts exact refnames. You
could work around it with a followup:

  git fetch --deepen 1

which is getting a bit convoluted. I suspect you may also have to
abandon the "checkout" action and do this manually. Definitely not worth
it compared to your solution for a PR, but maybe worth it if it lets us
do the same thing for arbitrary branches.

-Peff