From: Tom Jones <thj@freebsd.org>
Subject: Re: diff.git: Fix ed script output
To: gameoftrees@openbsd.org
Date: Tue, 30 Aug 2022 16:28:07 +0100

On Tue, Aug 30, 2022 at 05:19:29PM +0200, Stefan Sperling wrote:
> On Tue, Aug 30, 2022 at 02:47:58PM +0100, Tom Jones wrote:
> > Prior to this change ed script output was in the wrong order, i.e. in
> > the order diff_result provides and changes where missing added or
> > changed lines. ed edits need to be in reverse order to keep the edited
> > file in sync 
> 
> As it is, this patch breaks merging on Got, which relies on the
> existing output. The existing output is based on the 'ed-style'
> script which Caldera diff3(1) generates internally. As you've
> discovered this seems to not match traditional diff(1) ed output,
> which is unfortunate, and I was unaware of this when I added the
> ed output module for the purpose of supporting Got's merging code.
> 
> So we will need both variants. Should we add a flag?
> Or would providing two different ed-output modules be better?

Does the got version include the changed/added lines? The diff.git one
didn't, which made me think it didn't work.

In addition to ed script diff also has forward ed (-f) with mangled commands
and reverse ed (-n).

     -f --forward-ed
             Identical output to that of the -e flag, but in reverse order.
             It cannot be digested by ed(1).

     -n      Produces a script similar to that of -e, but in the opposite
             order and with a count of changed lines on each insert or delete
             command.  This is the form used by rcsdiff.

Is one of these the input that diff3 requires?

- Tom