Add using merge subtree How-To
[git/git.git] / Documentation / howto / using-merge-subtree.txt
1 Date: Sat, 5 Jan 2008 20:17:40 -0500
2 From: Sean <seanlkml@sympatico.ca>
3 To: Miklos Vajna <vmiklos@frugalware.org>
4 Cc: git@vger.kernel.org
5 Subject: how to use git merge -s subtree?
6 Abstract: In this article, Sean demonstrates how one can use the subtree merge
7 strategy.
8 Content-type: text/asciidoc
9 Message-ID: <BAYC1-PASMTP12374B54BA370A1E1C6E78AE4E0@CEZ.ICE>
10
11 How to use the subtree merge strategy
12 =====================================
13
14 There are situations where you want to include contents in your project
15 from an independently developed project. You can just pull from the
16 other project as long as there are no conflicting paths.
17
18 The problematic case is when there are conflicting files. Potential
19 candidates are Makefiles and other standard filenames. You could merge
20 these files but probably you do not want to. A better solution for this
21 problem can be to merge the project as its own subdirectory. This is not
22 supported by the 'recursive' merge strategy, so just pulling won't work.
23
24 What you want is the 'subtree' merge strategy, which helps you in such a
25 situation.
26
27 In this example, let's say you have the repository at `/path/to/B` (but
28 it can be an URL as well, if you want). You want to merge the 'master'
29 branch of that repository to the `dir-B` subdirectory in your current
30 branch.
31
32 Here is the command sequence you need:
33
34 ----------------
35 $ git remote add -f Bproject /path/to/B <1>
36 $ git merge -s ours --no-commit Bproject/master <2>
37 $ git read-tree --prefix=dir-B/ -u Bproject/master <3>
38 $ git commit -m "Merge B project as our subdirectory" <4>
39
40 $ git pull -s subtree Bproject master <5>
41 ----------------
42 <1> name the other project "Bproject", and fetch.
43 <2> prepare for the later step to record the result as a merge.
44 <3> read "master" branch of Bproject to the subdirectory "dir-B".
45 <4> record the merge result.
46 <5> maintain the result with subsequent merges using "subtree"
47
48 The first four commands are used for the initial merge, while the last
49 one is to merge updates from 'B project'.
50
51 Comparing 'subtree' merge with submodules
52 -----------------------------------------
53
54 - The benefit of using subtree merge is that it requires less
55 administrative burden from the users of your repository. It works with
56 older (before Git v1.5.2) clients and you have the code right after
57 clone.
58
59 - However if you use submodules then you can choose not to transfer the
60 submodule objects. This may be a problem with the subtree merge.
61
62 - Also, in case you make changes to the other project, it is easier to
63 submit changes if you just use submodules.
64
65 Additional tips
66 ---------------
67
68 - If you made changes to the other project in your repository, they may
69 want to merge from your project. This is possible using subtree -- it
70 can shift up the paths in your tree and then they can merge only the
71 relevant parts of your tree.
72
73 - Please note that if the other project merges from you, then it will
74 connects its history to yours, which can be something they don't want
75 to.