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From "Dawid Weiss (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-6933) Create a (cleaned up) SVN history in git
Date Wed, 16 Dec 2015 13:48:46 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-6933?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Dawid Weiss updated LUCENE-6933:
--------------------------------
    Description: 
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* deal with large binary blobs (JARs): keep empty files instead for their historical reference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}}).
* 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).


  was:
Goals:
- selectively drop unnecessary stuff from history (cms/, javadocs/, JARs and perhaps other
binaries),
- *preserve* history of all core sources. So svn log IndexWriter has to go back all the way
back to when Doug was young and pretty. Ooops, he's still pretty of course.
- provide a way to link git history with svn revisions. I would, ideally, include a "imported
from svn:rev XXX" in the commit log message.
- annotate release tags and branches. I don't care much about interim branches -- they are
not important to me (please speak up if you think otherwise).

Non goals
- no need to preserve "exact" history from SVN (the project may skip JARs, etc.). Ability
to build ancient versions is not an issue.


> 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
>
> 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}}).
> * 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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