94 lines
3.3 KiB
Text
94 lines
3.3 KiB
Text
From: Junio C Hamano <gitster@pobox.com>
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Subject: Separating topic branches
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Abstract: In this article, JC describes how to separate topic branches.
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Content-type: text/asciidoc
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How to separate topic branches
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==============================
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This text was originally a footnote to a discussion about the
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behaviour of the git diff commands.
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Often I find myself doing that [running diff against something other
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than HEAD] while rewriting messy development history. For example, I
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start doing some work without knowing exactly where it leads, and end
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up with a history like this:
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"master"
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o---o
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\ "topic"
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o---o---o---o---o---o
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At this point, "topic" contains something I know I want, but it
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contains two concepts that turned out to be completely independent.
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And often, one topic component is larger than the other. It may
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contain more than two topics.
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In order to rewrite this mess to be more manageable, I would first do
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"diff master..topic", to extract the changes into a single patch, start
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picking pieces from it to get logically self-contained units, and
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start building on top of "master":
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$ git diff master..topic >P.diff
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$ git checkout -b topicA master
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... pick and apply pieces from P.diff to build
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... commits on topicA branch.
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o---o---o
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/ "topicA"
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o---o"master"
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\ "topic"
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o---o---o---o---o---o
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Before doing each commit on "topicA" HEAD, I run "diff HEAD"
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before update-index the affected paths, or "diff --cached HEAD"
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after. Also I would run "diff --cached master" to make sure
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that the changes are only the ones related to "topicA". Usually
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I do this for smaller topics first.
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After that, I'd do the remainder of the original "topic", but
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for that, I do not start from the patchfile I extracted by
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comparing "master" and "topic" I used initially. Still on
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"topicA", I extract "diff topic", and use it to rebuild the
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other topic:
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$ git diff -R topic >P.diff ;# --cached also would work fine
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$ git checkout -b topicB master
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... pick and apply pieces from P.diff to build
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... commits on topicB branch.
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"topicB"
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o---o---o---o---o
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/
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/o---o---o
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|/ "topicA"
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o---o"master"
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\ "topic"
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o---o---o---o---o---o
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After I am done, I'd try a pretend-merge between "topicA" and
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"topicB" in order to make sure I have not missed anything:
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$ git pull . topicA ;# merge it into current "topicB"
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$ git diff topic
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"topicB"
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o---o---o---o---o---* (pretend merge)
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/ /
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/o---o---o----------'
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|/ "topicA"
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o---o"master"
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\ "topic"
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o---o---o---o---o---o
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The last diff better not to show anything other than cleanups
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for crufts. Then I can finally clean things up:
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$ git branch -D topic
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$ git reset --hard HEAD^ ;# nuke pretend merge
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"topicB"
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o---o---o---o---o
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/
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/o---o---o
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|/ "topicA"
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o---o"master"
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