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Re: Better interoperability with Bitkeeper for fast-import/-export





> On Jul 3, 2018, at 3:27 PM, Elijah Newren <newren@xxxxxxxxx> wrote:
> 
> Hi Philip,
> 
> On Tue, Jul 3, 2018 at 1:40 PM, Philip Prindeville
> <philipp_subx@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hi.
>> 
>> I tried to import into git a repo that I was working on (because it just seemed easier), but when I tried to export the repo back out after making my changes I found it choking on a few things.
>> 
>> It was explained to me (by the Bitkeeper folks) that git meta-data doesn’t accurately track file moves…  If a file disappears from one place and reappears in another with the same contents, that’s assumed to be a move.
>> 
>> Given that “git mv” is an explicit action, I’m not sure why that wouldn’t be explicitly tracked.
> 
> Not a full explanation, but see
> https://git-scm.com/book/en/v2/Git-Internals-Moving-Files


Why not add the logic to track moves/renames?  That link explains what it does, but not why it does it.


> 
>> But I’ve not looked too closely under the covers about how git represents stuff, so maybe there’s more to it than I’m assuming.
>> 
>> During an export using “-M” and “-C”, Bitkeeper complained:
> 
> Why would you add -C?  Does bitkeeper also track copies?


I figure that I’d furnish the maximum amount of meta data, and bitkeeper would use what it could and ignore the rest.


> 
>> fast-import: line 'R ports/winnt/libntp/nt_clockstuff.c ports/winnt/ntpd/nt_clockstuff.c' not supported
>> 
>> so I tried removing those two options, and it got further, this time stalling on:
>> 
>> fast-import: Unknown command: tag ntp-stable
> 
> If the fast-import command you are using can't read tags, then perhaps
> you should report that to the authors of the fast-import tool you are
> using and/or only feed branches to your fast-export command.


Well, I’ll just do branches for now…


> 
>> I like git, mostly because I’ve used it a lot more… and I like the GitHub service.  I use Bitkeeper because a few projects I work on are already set up to use it and it’s not my call whether it’s worth the effort to make the conversion or live with it.
>> 
>> So… this is an appeal for both to play better together.
>> 
>> What’s involved in getting git to track file/directory moves/renames so that it’s palatable to Bitkeeper?
> 
> Not tracking file/directory moves/renames wasn't an oversight but a
> fundamental design decision; see e.g.
> https://public-inbox.org/git/Pine.LNX.4.64.0510211826350.10477@xxxxxxxxxxx/.


"I'm convinced that git handles renames better than any other SCM ever. 
Exactly because we figure it out when it matters.”

I disagree.  When the move happens, there’s a commit message that goes along with that.  There’s an insight into why the move is happening.

That’s something that software can’t do for you.


> 
> However, supposing that we did track renames, how would we tell
> bitkeeper?  Well, we'd print out a line that looks like this in the
> fast-export:
> 
> 'R ports/winnt/libntp/nt_clockstuff.c ports/winnt/ntpd/nt_clockstuff.c'
> 
> which is precisely the line that bitkeeper's fast-import was choking
> on.  So, it sounds like they don't support importing rename
> information (or at least the version of fast-import you're using
> doesn't).  I think this is where the bug is; you'll probably want to
> report it to whoever maintains the fast-import command that is choking
> on this line.


Already done:

https://users.bitkeeper.org/t/using-fast-import-from-git-into-bk/907

Not sure I understand the response:

"The rename info that git gives us is a guess, that’s why there is that 0-100% next to it, that’s showing you how much of the two versions of the file were identical. So that info is unreliable, it’s just a guess."

Okay, what’s stopping them from doing their best with the information provided, even if it is a guess?

By the way, what happens when you interactively rebase a bunch of commits, change their order, and in the middle of an “edit”, do a “git mv … …” followed by a “git commit --amend && git rebase --continue”?

-Philip



> 
> Once that's fixed, you can export from git with the -M flag, and from
> that output, there'll be no way to tell whether the original
> repository tracked renames or detected them after the fact.
> 
> 
> Hope that helps,
> Elijah