On Fri, Aug 03, 2018 at 03:01:15PM +0300, Vadim Belov wrote:

> 1. This merges successfully without squash:
> git checkout origin/master
> git merge ${PR-Branch}
> git push origin HEAD:master
> git push origin --delete ${PR-Branch}

Right, this is a normal merge.

> 2. This closes the PR, but there is no update seen on master:
> git checkout origin/master
> git merge --squash --commit ${PR-Branch}
> git push origin HEAD:master
> git push origin --delete ${PR-Branch}

Doing "merge --squash --commit" doesn't do what you expect; namely
"--commit" does not override the non-committing nature of "--squash". It
only override a "--no-commit" found elsewhere.

IMHO this is something that could be improved in Git (i.e., telling the
difference between "the user did not say --no-commit" and "the user said
--commit" and respecting it for --squash).

But that explains what you see. The push to master is a noop, since you
didn't make a new commit. And then deleting the PR branch on GitHub
auto-closes the PR.

> 3. This fails to push to master with the error "GH006: Protected branch
> update failed"  (despite that the PR is set to SUCCESS):
> git checkout origin/master
> git merge --squash ${PR-Branch}
> git commit -am"comment"
> git push origin HEAD:${m_mainBranch}
> git push origin --delete ${m_prBranch}

So here you _do_ make an actual commit. But that commit doesn't look
like a merge to the receiver; it just looks like a single commit that
has all the changes there were on PR-Branch.

The tree of that commit should be the same tree that would result from a
real merge. So in theory things like protected-branch status checks
could handle that, but I suspect they use the actual commit id (the tree
id is fine if you're just doing CI, but if you wanted to have a status
check for commit messages, say, you'd obviously want that to be tied to
the actual commit object).

I don't offhand recall how that is implemented (and you could also be
falling afoul of other checks, like required reviews). But this is a
GitHub-specific question, and you should probably ask GitHub support to
go further.

-Peff