[darcs-users] hunk move as primitive change

[Petr Pudlák]

Hi,

an excellent idea. It has troubled me for a long time that when someone
moves a piece of code to another file, it's basically impossible to see if
there were any changes in the block or not without a very thorough
examination.

  Best regards,
  Petr


2013/5/1 Ben Franksen <benjamin.franksen at bessy.de>

> Hi Everyone
>
> This is something I have on my wish-list for longer than I can think. The
> idea is quite simple: a primitive change type that says "this sequence of
> lines moved from file X line N to file Y line M". Here, X and Y need not be
> different, i.e. a hunk move need not be between different files.
>
> To my knowledge no existing VCS has such a feature. There are two
> advantages
> I expect:
>
> (1) Moving code around is something I do regularly in the process of
> cleaning up my (or other's) code. Currently such changes are represented
> (e.g. when using record or whatsnew) as "remove these lines from file X
> line
> N (long block of code follows), add these lines to file Y line M (another
> long block of code follows)". The remove and insert changes need not even
> be
> adjacent to one another (they typically are not) and even if they are it is
> very hard for the human eye to spot small differences in a long stretch of
> text. So if the tool told me I have a move (or I could tell it that this is
> the case) then I could be confident that no functional change occurred.
>
> (2) A hunk move commutes with changes /inside/ the hunk, or at least I can
> see no reason why it should not. This is not the case for the way such a
> move is represented now (as a remove and insert). This would mean more
> changes commute and thus less (accidental, unwanted) conflicts.
>
> Even though the idea is simple, this is certainly not "low hanging fruit".
> It would be necessary to somehow record that the context for changes
> further
> down in the affected files translates up resp. down (by the number of lines
> moved), and to update this information when commuting such a change with
> other changes. On the other hand, for regular hunks we do that already, so
> maybe it is not that difficult after all. In any case adding a new
> primitive
> change type most probably counts as a "deep" change to the Darcs code; and
> I
> wonder if the repository format would have to be adapted and whether this
> could be done in a backward compatible way.
>
> BTW, a "better record command" as in the GSOC proposal (which I find very
> promising) could be tought to detect hunk moves and present them to the
> user
> as such. It could even propose to record a move if there /are/ additional
> changes inside such a moved hunk, i.e. separate the move from (minor)
> changes made to the affected lines, using some kind of similarity measure.
>
> I would love to hear what you think about that.
>
> Cheers
> --
> Ben Franksen
> ()  ascii ribbon campaign - against html e-mail
> /\  www.asciiribbon.org   - against proprietary attachm€nts
>
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