From: Stefan Sperling <stsp@stsp.name>
Subject: Re: diff -p function prototypes regression
To: Theo Buehler <tb@theobuehler.org>
Cc: gameoftrees@openbsd.org, Tom Jones <thj@freebsd.org>
Date: Tue, 22 Aug 2023 12:48:32 +0200

On Tue, Aug 22, 2023 at 11:57:48AM +0200, Theo Buehler wrote:
> diff -p is a hack, but it usually has helpful additional info.

And I am not trying to keep -p stuck in the way it is now. But the
change we applied did have unintended unfortunate side effects. I assume
FreeBSD's diff now has the same problems as you spotted in Got diff.

BSD diff -p has problems in many areas. Another issue are goto labels in C:
https://got.gameoftrees.org/?action=diff&commit=4e3e8516c9205eb93e0203a60fd74e271f567adb&headref=HEAD&path=got.git

If more thought and work was put into heuristics used by -p it could
be improved much further. For example, if -p took information about
the file's type into account (based on file name extensions that appear
in the diff) then language-specific heuristics could be implemented.
Heuristics for C could then be tweaked without affecting results for other
types of files such as Makefiles.

And such work needs to be done in a way that doesn't cause regressions,
which is the hard part...