From: Tupshin Harper <tupshin@tupshin.com>
Date: Tue, 19 Apr 2005 23:00:37 GMT
Subject: Re: Darcs and git: plan of action
Message-ID: <42658D95.7020404@tupshin.com>
In-Reply-To: <1113950442.29444.31.camel@orca.madrabbit.org>

Ray Lee wrote:

>Here's where we disagree. If you checkpoint your tree before the
>replace, and immediately after, the only differences in the
>source-controlled files would be due to the replace.
>
This is assuming that you only have one replace and no other operations 
recorded in the patch. If you have multiple replaces or a replace and a 
traditional diff  recorded in the same patch, then this is not true.

> And since the
>language of the file is known (and thereby the tokenization -- it *is*
>well-defined), then a tokenizer that compares the before and after trees
>(for just the files that changed, obviously), can discover what you did,
>and promote the mere ASCII diff into a token-replace diff. (The same
>sort of idea could be done for reindention, I'd hope.)
>  
>
See above for one set of limitations on this. A more fundamental problem 
comes back to intent. If I have a file "foo" before:
a1
a2
and after:
b1
b2
is that a "replace [_a-zA-Z0-9] a b foo" patch, or is that a
-a1
-a2
+b1
+b2
patch? Note that this comes down to heuristics, and no matter what you 
use, you will be wrong sometimes,  *and* the choice that is made can 
substantively affect the contents of the repository after additional 
patches are applied.

>We agree on everything except that it's provable that one can discover a
>replace operation, given a before and after tree.
>  
>
It's provable that you can not.

-Tupshin