Re: [PATCH 08/15] for-each-ref: get --pretty using format_commit_message

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 5, 2013, 17:09 UTC
Message-ID: <7v61xs32n0.fsf@alter.siamese.dyndns.org>
In-Reply-To: <CACsJy8ABwroExpXQRX8OYAnDum9+sX1+JB9z+WNn+YcZoXi5KA@mail.gmail.com>

Duy Nguyen <pclouds@gmail.com> writes:

Show 18 quoted lines

> On Wed, Jun 5, 2013 at 4:12 AM, Eric Sunshine <sunshine@sunshineco.com> wrote:
>>> +Caveats:
>>> +
>>> +1. Many of the placeholders in "PRETTY FORMATS" are designed to work
>>> +   specifically on commit objects: when non-commit objects are
>>> +   supplied, those placeholders won't work.
>>
>> Should "won't work" be expanded upon? It's not clear if this means
>> that git will outright crash, or if it will abort with an appropriate
>> error message, or if the directive will be displayed as-is or removed
>> from the output.
>
> It will be displayed as-is but that's a bit inconsistent: %(unknown)
> prints error and aborts while %unknown simply produces %unknown. The
> latter is how "git log --format" does it. But I think we could make
> for-each-ref --pretty to do the former for %unknown. It'll be
> consistent with %(unknown) and we do not need to elaborate much (it's
> pretty obvious when it does not work).

The Caveat Eric is asking about talks about "what happens to a %(field) that only makes sense for a commit when showing a ref pointing at a non-commit?", but you are answering "what happend to a %(invalidfield) that is not defined", aren't you?

IIRC, the reason we show literal from "log --format" is to make it easier for the person who misspelt %placeholder to spot it in the output, and also make it easier for the person who use %placeholder meant for newer versions of Git with an older one. It would be a bit unnice to die for the latter, especially if the format string is in a script or something.

To "log --format", all input objects are expected to be commits, so it does not have the "what does %(authordate) give when given a blob" issue.

But for "for-each-ref --format", it is perfectly normal that you may feed a non-commit; it makes the mechanism unusable if you errored out %(authordate) when showing a ref that points at a tag, doesn't it? Substituting an inapplicable placeholder with an empty string would be an easies way out, unless it learns a flexible/elaborate conditional formatting mechanism, I would think.