linux-kernel - Re: diffutils: C labels misdetected as functions

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Date:	Sun, 22 Jul 2007 14:30:00 -0700
From:	Junio C Hamano <gitster@...ox.com>
To:	Simon Arlott <simon@...e.lp0.eu>
Cc:	Paul Eggert <eggert@...UCLA.EDU>, Matthew Wilcox <matthew@....cx>,
	Denis Cheng <crquan@...il.com>,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
	git@...r.kernel.org
Subject: Re: diffutils: C labels misdetected as functions

Simon Arlott <simon@...e.lp0.eu> writes:

> On 22/07/07 19:38, Paul Eggert wrote:
>> 
>> Anyway, to work around your problem without changing "diff", you can
>> use "diff -u -F '^[[:alpha:]$_](|.*[^:])$'" instead of "diff -u -p".
>
> Perhaps git could do this (or similar) as a workaround? (Cc:ed)
>
>> Or you can put a single space before the labels in question: they'll
>> still stand out plenty.
>
> The code should definitely not need to be modified to work around a
> diff bug.

I think the word "bug" is just about documentation.  Promising
"show C function" and including labels and/or not showing all
functions would be a bug, but given that diff is about showing
textual differences between two text files with arbitrary kind
of contents, I do not think it is reasonable to take that "show
C function" promise too literally.

To avoid this, the description of the feature could be reworded
to "shows lines that match pattern '^[[:alpha:]$_]' on context
lines, intent of the option being that the pattern tends to
match the beginning of function in C language and help the
reader to locate the context more easily, with a caveat that the
pattern matching is not meant to capture all functions nor only
functions --- there will be false matches."

But that would be too long.  And as Paul showed, you can narrow
or widen the set of lines that are shown with the -F option.  I
do not think this deserves to be called a "bug".

You can define your own customized "function name" pattern in
your .git/config (or $HOME/.gitconfig) file to be used by the
git-diff family with recent enough git via the attributes
mechanism, but I do not think we should change the default,
unless GNU diff changes its default.  Personally I'd rather not
see it change, though.

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