Pre-receive hook from_ref all zeros

[sourcedelica]

In our pre-receive script sometimes we get a from_ref that is all zeros. For example

from_ref: 0000000000000000000000000000000000
to_ref: 96b9ac815489ab54390b4532f2904f90a98c

Should this be expected? If we pass this to git log it complains. Should we just ignore these rows?

[kovetskiy]

Hi, yes, it's expected behavior for all the git hooks, you can check githooks manual page: https://mirrors.edge.kernel.org/pub/software/scm/git/docs/githooks.html

where <old-value> is the old object name stored in the ref, <new-value> is the new object name to be stored in the ref and <ref-name> is the full name of the ref. When creating a new ref, <old-value> is 40 0.

So if you have from_ref which is equals to 40 0 it means that this is a new branch (ref) and it doesn't exist yet.

Here is how people often catch that: https://stackoverflow.com/a/20047273

[sourcedelica]

If there is a new branch with a few commits before the push, how can I find the commits since the from_ref is all zeros?

From https://github.com/reconquest/atlassian-external-hooks/issues/112 I was able to get it working in most cases like:

    if [[ ${from_ref} =~ ${new_branch_re} ]]; then   # all zeros
        from_ref=$(git rev-list --simplify-by-decoration -1 "${to_ref}")
    fi

But it seems like this is a heuristic that may not work if there are any other decorations added by the developer (tags, etc) before the push.

[kovetskiy]

Hey,

Check this example, it addresses the issue: https://external-hooks.reconquest.io/docs/example.bitbucket-require-commits-to-be-associated-with-a-jira-issue/

Specifically this piece:

    if [[ "$from_ref" == "$z40" ]]; then
        # if it is a new branch then check all branch related commits
        boundaries=($(git rev-list --simplify-by-decoration -2 "$to_ref"))
        commits=($(git rev-list "${boundaries[0]}".."$to_ref"))

[sourcedelica]

Thanks. Since that logic is using the first (boundaries[0]) hash of two (-2) would it also be accurate to simplify to this?

    if [[ "$from_ref" == "$z40" ]]; then
        # if it is a new branch then check all branch related commits
        from_ref=$(git rev-list --simplify-by-decoration -1 "$to_ref")
        commits=($(git rev-list $from_ref..$to_ref))

[kovetskiy]

@sourcedelica right, I think it would be even better :+1:

[sourcedelica]

Thanks for the confirmation and the solution. —simplify-by-decoration is a clever approach to the problem.

[sourcedelica]

It appears that --simplify-by-decoration is a heuristic but not perfect. It will walk back to the first decorated commit which would be a tag, a merge commit or a branch head. In many cases it walks back further than needed because the parent branch head is probably move ahead of the fork point. So it hits the most recent merge commit.