Re: backwards compatibility, was Re: [PATCH v1 1/3] Introduce config variable "diff.primer"

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

On Mon, 26 Jan 2009, Jeff King wrote:

> On Mon, Jan 26, 2009 at 11:59:46AM +0100, Johannes Schindelin wrote:
> 
> > Just a reminder: we are very conservative when it comes to breaking 
> > backwards compatibility.  For example, people running (but not upgrading) 
> > gitweb who want to upgrade Git may rightfully expect their setups not to 
> > be broken for a long time, if ever.
> 
> Are you aware that gitweb no longer calls "git diff", exactly because
> of problems caused by calling a porcelain from a script?

As I said: do you really expect people not to forget to upgrade gitweb 
manually when they do "sudo make install" with a new Git version?

> I don't want to break existing setups, either. But at some point you 
> have to say "this is porcelain, so don't rely on there not being any 
> user-triggered effects in its behavior". If porcelain is cast in stone, 
> then what is the point in differentiating plumbing from porcelain?

Two points there:

- with gitweb, we were the offenders ourselves.  So we should give the 
  users of gitweb at least _some_ slack.

- Concretely for the "porcelain" git diff: This workflow

	git diff > my-patch
	<attach and send to somebody>

  is probably pretty wide spread.  And it is okay, a user is not a script, 
  they are very much allowed to use porcelain.  And we _would_ break 
  expectations there.

Now, I have another two, fundamental problems with the diff options 
defaults: you are restricting the thing to _one_ set of options, and when 
somebody wants to run without those options, she has to actively _undo_ 
them.

Remember, sometimes you need another set of options. Like, when I send 
mail to a Git user, I want "-M -C -C", when I send mail to a non-Git user, 
I do not want any additional options (and try to undo "-M -C -C" on the 
command line, good luck), and sometimes it is much easier to see what 
happened with a word diff.

So what I need are three different sets of diff options.

Guess how well that works with aliases -- we are talking command line 
here after all, right?

Ciao,
Dscho