bzr check should verify last-changed fields and per file knit parents.

[John Arbash Meinel]

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Robert Collins wrote:
> In bzr.dev we have inconsistent data between the inventory and per-file
> graphs.
> 
> Specifically, in one revision X, which is a merge of 'A' and 'B', a file
> which was modified on both sides (presumably to the same content) is
> recorded with last-changed of 'A', rather than last-changed of 'X'.
> 
> This is a problem, because the revision X in the per-file knits is
> apparently referred to to recreate subsequent revisions.
> 
> So check should perform some sanity checks. A cheap one to do is:
> every file-knit revision referenced from each inventory should be
> checked for existence; AND if the revision referenced is not the one
> introduced by the revision, there MUST NOT be a file-revision in the
> repository with that revision.
> 
> that is, per-file-knit referenced, take the set difference of
> seen-revisions-in-inventories and versions-in-the-knit, then intersect
> that with seen-revisions - the result must be empty.
> 
> Until check catches this we cannot fix push and pull to do partial index
> reads of repositories. We may need to bump the repository format or
> something as a way to say 'this repository has been checked for this
> defect'.
> 
> Please follow up to the list only, we only need a single bug filed :)
> 
>  affects /products/bzr
>  importance critical

Sounds reasonable.
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