Re: Darcs and git: plan of action

From: Tupshin Harper <tupshin@tupshin.com>
Date: Apr 19, 2005, 23:00 UTC
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.

Show 8 quoted lines

> 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