Scenario: upstream-rewritten-equal-tree

The upstream rewrote its history and force-pushed a new commit with exactly the same files. The splice looks up to date, but its synced commit is no longer part of the upstream's history. A merge or pull records the new commit as the synced commit, so the next change builds on the rewritten history (#17).

That only works while the folder still has the upstream's files. After a local change, the splice is unrelated history, and merge and pull refuse to guess. Then keep the upstream's version and redo the local changes on top of it. If the rewrite removed something, like a secret, don't use the other ways out that merge prints (#38). git splice push --force rebuilds on top of the old synced commit, and so publishes the rewritten-away history again. Keeping both publishes the monorepo's own history of the folder, which contains whatever the monorepo pulled before the rewrite.

Output

setup.bash builds this state:

$ build_scenario scenario_upstream_rewritten_equal_tree

The monorepo's a records r, the old release on top of k; T is w, the rewritten release, a root commit of its own

$ git -C "$UPSTREAM" log --format=%s main
w: release, history rewritten

The splice is up to date: the folder has the upstream's files.

$ git splice status
On branch main

  up to date  vendor/a

But .splice names the old release, r, which the upstream's history no longer contains. The upstream's main, as fetched, is the ref ending in /main:

$ main="$(
>   git for-each-ref --format='%(refname:lstrip=4) %(objectname)' refs/splices/ |
>     sed -n 's#^main ##p'
> )"

$ synced="$(git config --file vendor/a/.splice splice.commit)" &&
>   git merge-base --is-ancestor "$synced" "$main" || echo "not in the upstream's history"
not in the upstream's history

A merge records the rewritten commit as the synced commit, in a commit that changes only .splice:

$ git splice merge vendor/a
ok   vendor/a: recorded 5cc12da as the synced commit -- the folder already has its files

$ git show --stat --format=%s HEAD
splice: merge vendor/a from main at 5cc12da

 vendor/a/.splice | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

A local change now builds on the rewritten history:

$ echo "local change" >>vendor/a/file.txt && git commit -q -a -m "local change"

$ git splice push vendor/a
ok   vendor/a: pushed 2a8eb25 to main

$ git -C "$UPSTREAM" log --format=%s main
local change
w: release, history rewritten

Output​

Output