Christian Couder c20f112e51 fast-import: add 'strip-if-invalid' mode to --signed-commits=<mode> ...

Tools like `git filter-repo`[1] use `git fast-export` and
`git fast-import` to rewrite repository history. When rewriting
history using one such tool though, commit signatures might become
invalid because the commits they sign changed due to the changes
in the repository history made by the tool between the fast-export
and the fast-import steps.

Note that as far as signature handling goes:

  * Since fast-export doesn't know what changes filter-repo may make
to the stream, it can't know whether the signatures will still be
valid.

  * Since filter-repo doesn't know what history canonicalizations
fast-export performed (and it performs a few), it can't know whether
the signatures will still be valid.

  * Therefore, fast-import is the only process in the pipeline that
can know whether a specified signature remains valid.

Having invalid signatures in a rewritten repository could be
confusing, so users rewritting history might prefer to simply
discard signatures that are invalid at the fast-import step.

For example a common use case is to rewrite only "recent" history.
While specifying commit ranges corresponding to "recent" commits
could work, users worry about getting it wrong and want to just
automatically rewrite everything, expecting older commit signatures
to be untouched.

To let them do that, let's add a new 'strip-if-invalid' mode to the
`--signed-commits=<mode>` option of `git fast-import`.

It would be interesting for the `--signed-tags=<mode>` option to
have this mode too, but we leave that for a future improvement.

It might also be possible for `git fast-export` to have such a mode
in its `--signed-commits=<mode>` and `--signed-tags=<mode>`
options, but the use cases for it are much less clear, so we also
leave that for possible future improvements.

For now let's just die() if 'strip-if-invalid' is passed to these
options where it hasn't been implemented yet.

[1]: https://github.com/newren/git-filter-repo

Helped-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2025-11-26 08:43:44 -08:00

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