[PATCH v3 0/5] fast-import: start controlling how tag signatures are handled

Introduction ------------

Tools like `git-filter-repo` should be able to control how tag signatures are handled when regenerating repository content after it has been filtered. For this purpose, they need a way for `git fast-import` to control how tag signatures are handled.

A previous series [1] added a '--signed-commits=<mode>' option to `git fast-import` to control how commit signatures are handled, so this is adding a similar '--signed-tags=<mode>' for tag signatures.

For now this new option behaves in a very similar way as the option with the same name that already exists in `git fast-export`. Especially it supports exactly the same <mode>s and the same aliases for these modes. For example "ignore" is a synonym for "verbatim".

This way, both `git fast-export` and `git fast-import` have both a '--signed-tags=<mode>' and a '--signed-commits=<mode>' supporting the same <mode>s.

In the future I want to implement new <mode>s like "strip-if-invalid", "re-sign", "re-sign-if-invalid" in `git fast-import` for both tag and commit signatures. These might be a bit more complex, so for now I prefer to start with the simple modes.

[1] https://lore.kernel.org/git/20250917181427.3193500-1-christian.couder@gmail.com/

Note about the different patches --------------------------------

Patch 1/5 (doc: git-tag: stop focussing on GPG signed tags) is a documentation update for `git tag`. It could go in a separate series or be dropped altogether, but while working on this I thought that it would be a good thing to do, as the doc is quite outdated.

Patches 2/5, 3/5 and 4/5 are preparatory patches for the main one which is patch 5/5 (fast-import: add '--signed-tags=<mode>' option).

I wanted '--signed-tags=<mode>' to work for all kinds of signature in tags (OpenPGP, X.509 and SSH) but soon realized that the '--signed-tags=<mode>' option of `git fast-export` worked only for OpenPGP signatures, so I fixed that issue in patch 4/5 (fast-export: handle all kinds of tag signatures).

While working on the tests in patch 4/5, I found a few things to improve that could belong to other patches so that's how I came up with patches 2/5 and 3/5.

Changes since v2 ----------------

Thanks to Patrick Steinhardt, Todd Zullinger and Collin Funk who reviewed or commented on the v1 and v2.

There is a single change in the first patch (doc: git-tag: stop focusing on GPG signed tags) where the description of the `-v | --verify` option of `git tag` has been improved.

CI tests --------

I haven't run CI tests because there is a single documentation change since v2 that is very unlikely to make things break.

Range diff since v2 -------------------

1:  eb65af631d ! 1:  ac67d927ad doc: git-tag: stop focusing on GPG signed tags
    @@ Documentation/git-tag.adoc: OPTIONS
      -v::
      --verify::
     -  Verify the GPG signature of the given tag names.
    -+  Verify the signature of the given tag names.
    ++  Verify the cryptographic signature of the given tags.
      
      -n<num>::
        <num> specifies how many lines from the annotation, if any,
2:  640204ef26 = 2:  f0208527ff lib-gpg: allow tests with GPGSM or GPGSSH prereq first
3:  8f788bafe1 = 3:  e9e3d8c081 t9350: properly count annotated tags
4:  d62a43905c = 4:  8d318a0046 fast-export: handle all kinds of tag signatures
5:  9094f37b46 = 5:  962ad96b4a fast-import: add '--signed-tags=<mode>' option

Christian Couder (5):
  doc: git-tag: stop focusing on GPG signed tags
  lib-gpg: allow tests with GPGSM or GPGSSH prereq first
  t9350: properly count annotated tags
  fast-export: handle all kinds of tag signatures
  fast-import: add '--signed-tags=<mode>' option

 Documentation/git-fast-import.adoc |  5 ++
 Documentation/git-tag.adoc         | 48 ++++++++++++------
 builtin/fast-export.c              |  7 ++-
 builtin/fast-import.c              | 43 ++++++++++++++++
 t/lib-gpg.sh                       | 24 +++++++--
 t/meson.build                      |  1 +
 t/t9306-fast-import-signed-tags.sh | 80 ++++++++++++++++++++++++++++++
 t/t9350-fast-export.sh             | 48 ++++++++++++++++--
 8 files changed, 229 insertions(+), 27 deletions(-)
 create mode 100755 t/t9306-fast-import-signed-tags.sh