From: Linus Torvalds <torvalds@osdl.org>
Date: Wed, 18 May 2005 15:41:21 GMT
Subject: Re: [PATCH 0/1] Diff-helper update
Message-ID: <Pine.LNX.4.58.0505180821470.18337@ppc970.osdl.org>
In-Reply-To: <7v3bslqc94.fsf@assigned-by-dhcp.cox.net>



On Tue, 17 May 2005, Junio C Hamano wrote:
>
> This is just a cover letter but the next patch implements the
> rename detection I told you about.

Ok. I now have one more worry: git-diff-tree with "--stdin".

I actually find that thing to be surpremely useful, and I use it for not 
just my silly git-whatchanged script, but also to make release notes. I 
just do

	git-rev-tree HEAD ^LAST_RELEASE | cut -d' ' -f2 | git-diff-tree -v -s --stdin

and that's wonderful. And sometimes I use "-p" instead of "-s", because 
I'm not making release notes, but because I'm doing a "whatchanged" with 
full diffs.

In other words, try something like this on the kernel tree:

	git-whatchanged -p include/asm-i386 arch/i386 | less -S

and stare in wonder at just how _useful_ this simple thing is.

Maybe it's just that I've not used all that many different SCM systems,
and I've certainly not used all the features of the ones I _have_ used, so
maybe I never knew, but dammit, I've never seen anybody else do something
quite that useful (at least doing it fast enough that it _remains_
useful).

(Replace "arch/i386" with "drivers/usb" or "fs/ext3" or whatever,
depending on just what your area of interest happens to be).

In other words, I'm very happy with git.

However, git-diff-helper doesn't understand these things, and the builtin
diff doesn't do the rename thing. Yet it would be very very useful to do.

Now, if you do just a

	git-whatchanged include/asm-i386 arch/i386

(or you can even use "-z" if you want to), it turns out hat git-diff-tree 
actually does output perfectly usable material. Each "set of diffs" is 
clearly separated, and there is no ambiguos material: all lines are 
either:
 - empty or start with a whitespace
 - start with "diff-tree ", "Author: " or "Date: "
 - are valid input for diff-helper

So what I'd suggest is one (or both) of two possibilities:
 - make the internal diff logic also able to do the same rename handling 
   as the external diff-helper. This may or may not be complex, I've not 
   looked at it.
 - change diff-helper subtly: instead of printing "cannot parse %s", any
   nonrecognized line would be a "ignore this line, but process all
   pending potential renames".

The above would mean that I could either just do

	git-whatchanged include/asm-i386 arch/i386 | git-diff-helper

or continue to use

	git-whatchanged -p include/asm-i386 arch/i386

and still get the "nice" output (and it's a _feature_ that a rename within
the arch/i386 then shows up as a rename, but a rename that crosses the
boundary shows up as a "create" or "delete" event).

Comments? 

			Linus