In article <alpine.LFD.2.00.1002031436490.1681@xxxxxxxxxxx>,
Nicolas Pitre <nico@xxxxxxxxxxx> wrote:
> On Wed, 3 Feb 2010, Ron Garret wrote:
>
> > So... how *does* git decide when two blobs are different blobs and when
> > they are the same blob with mods? I asked this question before and was
> > pointed to the diffcore docs, but that didn't really clear things up.
> > That just describes all the different ways git can do diffs, not the
> > actual heuristics that git uses to track content.
>
> Yes, those same heuristics are used to make the decision.
>
> |The second transformation in the chain is diffcore-break, and is
> |controlled by the -B option to the 'git diff-{asterisk}' commands.
> |This is used to detect a filepair that represents "complete rewrite"
> |and break such filepair into two filepairs that represent delete and
> |create.
> |[...]
>
> |This transformation is used to detect renames and copies, and is
> |controlled by the -M option (to detect renames) and the -C option
> |(to detect copies as well) to the 'git diff-{asterisk}' commands.
> |[...]
>
> Note that you may use the -B, -C, -M and --find-copies-harder arguments
> with log as well as diff commands even if there is no actual diff
> output. So the explanation is really in that document even if simple
> rename detection is concerned only by a fraction of what is said there.
>
> And Git can detect copied files too.
>
> Those semantics are not stored in the repository so they can be improved
> or even changed after the facts.
OK, on closer reading I see that the information is there, but it's well
hidden :-) (For example, the -M option takes an optional numerical
argument so you can tweak how much similarity is needed to be considered
a move. But the docs for git log don't mention this. It's buried deep
in the git diffcore docs. But yes, it's there.)
So I think I'm beginning to understand how this works, but that leads me
to another question: it seems to me that there are potential screw cases
for this purely content-based system of tracking files. For example,
suppose I have a directory full of sample config files, all of which are
similar to each other. Will that cause diffcore to get confused?
Feel free to treat that as a rhetorical question because obviously I can
(and probably should) get the answer by trying it.
Thanks!
rg
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