in particular, when reviewing a file with a revocation certificate, --show-keys actually imports it:
mkdir -m 0700 a b gpg --homedir $(pwd)/a --yes --batch --passphrase abc123 --pinentry-mode loopback --quick-gen-key 'this is a test' gpg --homedir a --export | gpg --homedir b --import gpg --homedir b --list-keys sed 's/^:-----/-----/' < a/openpgp-revocs.d/*.rev | gpg --homedir b --with-colons --show-keys gpg --homedir b --list-keys
the above command shows the key as revoked in the second run.
however, if i use the following instead of the --show-keys invocation:
sed 's/^:-----/-----/' < a/openpgp-revocs.d/*.rev | gpg --homedir b --with-colons --dry-run --import-options import-show --import
then the keyring is unchanged.