Subject: Re: [PATCH] blame: fix unblamable and ignored lines in porcelain mode

From: Junio C Hamano <[email-masked]>
Date: Sun, 23 Mar 2025 08:58:03 -0700

Karthik Nayak <[email-masked]> writes:

> However, this option was never extended to the porcelain mode of
> 'git-blame(1)'. Since the documentation does not indicate this
> exclusion, it is a bug.

I agree it is a bug when people added ignore or unblamable support
that they did not _consider_ what to do with their new pieces of
information to help porcelain writers.  It is not a bug in the code
per-se, but it is a bug in the brain of these people ;-)

But prefixing random garbage to the commit object name line in the
porcelain mode output does not sound like the right solution to the
bug, either.

When enhancing an existing output format, make sure that your
changes will have minimum empact to existing parsers that do not
know about your extension.  It is reasonably expected that existing
Porcelain scripts reading from --porcelain mode output works by

 - Recognizing a line that match "^[0-9a-f]{40} \d+ \d+ \d+$" and
   take it as the beginning of a new record;

 - Collect all info lines before the payload line.  Lines that
   describe per-commit information are not repeated if it is already
   shown, so remember them when you see the commit for the first
   time, and recall them when you recognize the commit you already
   saw.

 - A payload line is indented with HT and terminates the record.

If you start to add unrecognizable garbage to the line with very
well known fixed format that is used as record delimiter, you would
break the existing parsers, which is not a very nice thing to do.
Are there other and better ways you can think of to add new pieces
of information like this in a way with less severe damage?