Teach 'git merge' and 'git pull' the option --ff-only
For convenience in scripts and aliases, add the option
--ff-only to only allow fast-forwards (and up-to-date,
despite the name).
Disallow combining --ff-only and --no-ff, since they
flatly contradict each other.
Allow all other options to be combined with --ff-only
(i.e. do not add any code to handle them specially),
including the following options:
* --strategy (one or more): As long as the chosen merge
strategy results in up-to-date or fast-forward, the
command will succeed.
* --squash: I cannot imagine why anyone would want to
squash commits only if fast-forward is possible, but I
also see no reason why it should not be allowed.
* --message: The message will always be ignored, but I see
no need to explicitly disallow providing a redundant message.
Acknowledgements: I did look at Yuval Kogman's earlier
patch (107768 in gmane), mainly as shortcut to find my
way in the code, but I did not copy anything directly.
Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>