fast-import: add mode to sign commits with invalid signatures

With git-fast-import(1), handling of signed commits is controlled via
the `--signed-commits=<mode>` option. When an invalid signature is
encountered, a user may want the option to sign the commit again as
opposed to just stripping the signature. To facilitate this, introduce a
"sign-if-invalid" mode for the `--signed-commits` option. Optionally, a
key ID may be explicitly provided in the form
`sign-if-invalid[=<keyid>]` to specify which signing key should be used
when signing invalid commit signatures.

Note that to properly support interoperability mode when signing commit
signatures, the commit buffer must be created in both the repository and
compatability object formats to generate the appropriate signatures
accordingly. As currently implemented, the commit buffer for the
compatability object format is not reconstructed and thus signing
commits in interoperability mode is not yet supported. Support may be
added in the future.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/gpg-interface.h b/gpg-interface.h
index 37f3ac42db..a365586ce1 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -120,12 +120,15 @@ enum sign_mode {
 	SIGN_WARN_STRIP,
 	SIGN_STRIP,
 	SIGN_STRIP_IF_INVALID,
+	SIGN_SIGN_IF_INVALID,
 };
 
 /*
  * Return 0 if `arg` can be parsed into an `enum sign_mode`. Return -1
- * otherwise.
+ * otherwise. If the parsed mode is SIGN_SIGN_IF_INVALID and GPG key provided in
+ * the arguments in the form `sign-if-invalid=<keyid>`, the key-ID is parsed
+ * into `char **keyid`.
  */
-int parse_sign_mode(const char *arg, enum sign_mode *mode);
+int parse_sign_mode(const char *arg, enum sign_mode *mode, const char **keyid);
 
 #endif