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Re: [BUG] Data loss when committing a new file which is a target of multiple merges

From: Philip Martin <philip_at_codematters.co.uk>
Date: 2006-07-12 21:11:06 CEST

Lieven Govaerts <lgo@mobsol.be> writes:

> Daniel Rall wrote:
>> On Wed, 12 Jul 2006, Lieven Govaerts wrote:
>>> Philip Martin wrote:
>>>> The copyfrom revision is more of a problem. I suppose the ranges A:B
>>>> and B:C could combine to give A:C, but what about A:B and C:D when
>>>> B!=C and none of the revisions between B:C affect the target? What if
>>>> C<B but none of the duplicate revisions affect the target? If we do
>>>> decide to update the copyfrom data it's not as simple as just updating
>>>> the revision, the text-base will also need to be updated
>>> Can you give me a (high-level) scenario and which the user
>>> experiences this problem?
>> The "Steps to reproduce" in my original mail describes the specific
>> steps. Given Philip's findings, in practice this problem would only
>> be triggered by by a programmatic operation, likely some type of
>> quickly-executing VC/SCM automation which doesn't do any range
>> combining when applying merges to a WC (e.g. automated merging for an
>> integration branch).
> While my test passes on my machine (it's probably slow enough) I also
> see that the copyfrom revision is filled in incorrectly. So my
> question is, given the fact that the copyfrom revision is filled in
> incorrectly, what problems can this give for the user? That way I can
> add such a problem scenario to the test, mark it as XFAIL and commit
> it to the repository.

It's not really clear that the copyfrom revision is a bug; I don't
think we have ever claimed that successive merges would update it.
Your idea of identifying A:B followed by B:C as equivalent to A:C
works in one particular case but I'm not sure it's a general solution.
What happens if the copyfrom is the result of an explict user copy
rather than a merge, is it still acceptable for merge to change the
copyfrom revision?

Philip Martin
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Received on Wed Jul 12 21:11:39 2006

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