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https://issues.apache.org/jira/browse/LUCENE-6933?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15064797#comment-15064797
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Dawid Weiss commented on LUCENE-6933:
-------------------------------------
Oops, sorry. I misread your comment. I don't know. will look into it tomorrow.
> Create a (cleaned up) SVN history in git
> ----------------------------------------
>
> Key: LUCENE-6933
> URL: https://issues.apache.org/jira/browse/LUCENE-6933
> Project: Lucene - Core
> Issue Type: Task
> Reporter: Dawid Weiss
> Assignee: Dawid Weiss
> Attachments: migration.txt, multibranch-commits.log, tools.zip
>
>
> Goals:
> * selectively drop projects and core-irrelevant stuff:
> ** {{lucene/site}}
> ** {{lucene/nutch}}
> ** {{lucene/lucy}}
> ** {{lucene/tika}}
> ** {{lucene/hadoop}}
> ** {{lucene/mahout}}
> ** {{lucene/pylucene}}
> ** {{lucene/lucene.net}}
> ** {{lucene/old_versioned_docs}}
> ** {{lucene/openrelevance}}
> ** {{lucene/board-reports}}
> ** {{lucene/java/site}}
> ** {{lucene/java/nightly}}
> ** {{lucene/dev/nightly}}
> ** {{lucene/dev/lucene2878}}
> ** {{lucene/sandbox/luke}}
> ** {{lucene/solr/nightly}}
> * preserve the history of all changes to core sources (Solr and Lucene).
> ** {{lucene/java}}
> ** {{lucene/solr}}
> ** {{lucene/dev/trunk}}
> ** {{lucene/dev/branches/branch_3x}}
> ** {{lucene/dev/branches/branch_4x}}
> ** {{lucene/dev/branches/branch_5x}}
> * provide a way to link git commits and history with svn revisions (amend the
> log message).
> * annotate release tags
> * deal with large binary blobs (JARs): keep empty files instead for their
> historical reference only.
> Non goals:
> * no need to preserve "exact" merge history from SVN (see "impossible" below).
> * Ability to build ancient versions is not an issue.
> Impossible:
> * It is not possible to preserve SVN "merge history" because of the following
> reasons:
> ** Each commit in SVN operates on individual files. So one commit can
> "copy" (and record a merge) files from anywhere in the object tree, even
> modifying them along the way. There simply is no equivalent for this in git.
> ** There are historical commits in SVN that apply changes to multiple
> branches in one commit ({{r1569975}}) and merges *from* multiple branches in
> one commit ({{r940806}}).
> * Because exact merge tracking is impossible then what follows is that exact
> "linearized" history of a given file is also impossible to record. Let's say
> changes X, Y and Z have been applied to a branch of a file A and then merged
> back. In git, this would be reflected as a single commit flattening X, Y and
> Z (on the target branch) and three independent commits on the branch. The
> "copy-from" link from one branch to another cannot be represented because, as
> mentioned, merges are done on entire branches in git, not on individual
> files. Yes, there are commits in SVN history that have selective file merges
> (not entire branches).
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