Re: [RFC PATCH 3/4] color.ui config: don't die on unknown values

From: Junio C Hamano <gitster@pobox.com>
Date: May 30, 2018, 23:05 UTC
Message-ID: <xmqqin74d9rh.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20180530210641.19771-4-avarab@gmail.com>

Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:

> Before this change git will die on any unknown color.ui values:
>
>     $ git -c color.ui=doesnotexist show
>     fatal: bad numeric config value 'doesnotexist' for 'color.ui': invalid unit

I do not think "unit" is correct, so there may be some room for improvement. For _this_ particular case, I agree that it is not the end of the world if we did not color the output (because we do not know what the 'doesnotyetexist' token from the future is trying to tell us), but as a general principle, we should diagnose and die, if a misconfiguration is easy to correct, than blindly go ahead and do random things that the end-user did not expect by giving something we do not (but they thought they do) understand.

If we really want to introduce "here is a setting you may not understand, in which case you may safely ignore", the right way to do so is to follow the model the index extension took, where from the syntax of the unknown thing an old/existing code can tell if it is optional. Forcing all codepaths to forever ignore what they do not understand and what they happen to think is a safe fallback is simply being irresponsible---the existing code does not understand the new setting so they do not even know if their "current behaviour" as a fallback is a safe and sensible one from the point of view of the person who asked for the feature from the future.