• g10/delkey.c (should_skip): New.

(do_delete_key): Skip keys other than the exact key specified by user.

When the user tries to delete a specific secret subkey
by using an exact search specification (trailing "!"),
gpg deletes the primary key and all other subkeys as well.

The new should_skip static function allows the key deletion routine
to determine when to skip keys. In this case, keys are skipped when
they are not the exact key specified by the user.

Signed-off-by: Matheus Afonso Martins Moreira <matheus.a.m.moreira@gmail.com>

Given a temporary gpg home with primary and subordinate keys:

$ agent/gpg-agent --daemon --homedir $XDG_RUNTIME_DIR/gnupg-git
$ g10/gpg --homedir $XDG_RUNTIME_DIR/gnupg-git --batch --passphrase '' --default-new-key-algo 'rsa1024/cert+rsa1024/sign' --quick-gen-key test
$ SUBKEY=$(g10/gpg --homedir $XDG_RUNTIME_DIR/gnupg-git -K --with-subkey-fingerprint --with-colons | awk -F: '/fpr/ { print $10 }' | tail -1)

Deleting just the secret subkey should leave the primary key intact:

$ g10/gpg --homedir $XDG_RUNTIME_DIR/gnupg-git --batch --yes --delete-secret-keys $SUBKEY!
$ g10/gpg --homedir $XDG_RUNTIME_DIR/gnupg-git -K
sec   rsa1024 2019-05-02 [C] [expires: 2021-05-01]
uid           [ultimate] test
ssb#  rsa1024 2019-05-02 [S]