Will commits in git and mercurial repositories with the same history have the same hash?

Question

When using git to clone an hg repository, or when migrating from hg to git, will the hashes remain the same?

Answer 1

By inspection, the answer appears to be "no".

hg clone ssh://some.server.com/path/hgproject/

git clone hg::ssh://some.server.com/path/hgproject/

Followed by:

hg log -l 5

git log -n 5

Show different commit hashes for the same commits.

While both git and hg use SHA-1 hashes, there must be a difference in what they are hashing, perhaps the metadata.

Any tooling dependent on the hashes will require history rewriting for a migration.

More in depth context

Per comment by @ngoldbaum & https://www.mercurial-scm.org/wiki/Nodeid:

nodeid = sha1( min(parent1, parent2) + max(parent1, parent2) + contents )

Whereas git computes it as:

sha1(
    meta data
        commit message
        committer
        commit date
        author
        authoring date
    hash-of-tree-object (effectively the working directory)
)

Mapping

if using git-remote-hg to do the view or conversion you can find enough information to create a mapping in .git/hg/origin/marks-{hg,git}