Documentation/merge-strategies.txt

   1 MERGE STRATEGIES
   2 ----------------
   3
   4 The merge mechanism (`git merge` and `git pull` commands) allows the
   5 backend 'merge strategies' to be chosen with `-s` option.  Some strategies
   6 can also take their own options, which can be passed by giving `-X<option>`
   7 arguments to `git merge` and/or `git pull`.
   8
   9 resolve::
  10         This can only resolve two heads (i.e. the current branch
  11         and another branch you pulled from) using a 3-way merge
  12         algorithm.  It tries to carefully detect criss-cross
  13         merge ambiguities and is considered generally safe and
  14         fast.
  15
  16 recursive::
  17         This can only resolve two heads using a 3-way merge
  18         algorithm.  When there is more than one common
  19         ancestor that can be used for 3-way merge, it creates a
  20         merged tree of the common ancestors and uses that as
  21         the reference tree for the 3-way merge.  This has been
  22         reported to result in fewer merge conflicts without
  23         causing mismerges by tests done on actual merge commits
  24         taken from Linux 2.6 kernel development history.
  25         Additionally this can detect and handle merges involving
  26         renames.  This is the default merge strategy when
  27         pulling or merging one branch.
  28 +
  29 The 'recursive' strategy can take the following options:
  30
  31 ours;;
  32         This option forces conflicting hunks to be auto-resolved cleanly by
  33         favoring 'our' version.  Changes from the other tree that do not
  34         conflict with our side are reflected to the merge result.
  35         For a binary file, the entire contents are taken from our side.
  36 +
  37 This should not be confused with the 'ours' merge strategy, which does not
  38 even look at what the other tree contains at all.  It discards everything
  39 the other tree did, declaring 'our' history contains all that happened in it.
  40
  41 theirs;;
  42         This is the opposite of 'ours'; note that, unlike 'ours', there is
  43         no 'theirs' merge stragegy to confuse this merge option with.
  44
  45 patience;;
  46         With this option, 'merge-recursive' spends a little extra time
  47         to avoid mismerges that sometimes occur due to unimportant
  48         matching lines (e.g., braces from distinct functions).  Use
  49         this when the branches to be merged have diverged wildly.
  50         See also linkgit:git-diff[1] `--patience`.
  51
  52 diff-algorithm=[patience|minimal|histogram|myers];;
  53         Tells 'merge-recursive' to use a different diff algorithm, which
  54         can help avoid mismerges that occur due to unimportant matching
  55         lines (such as braces from distinct functions).  See also
  56         linkgit:git-diff[1] `--diff-algorithm`.
  57
  58 ignore-space-change;;
  59 ignore-all-space;;
  60 ignore-space-at-eol;;
  61 ignore-cr-at-eol;;
  62         Treats lines with the indicated type of whitespace change as
  63         unchanged for the sake of a three-way merge.  Whitespace
  64         changes mixed with other changes to a line are not ignored.
  65         See also linkgit:git-diff[1] `-b`, `-w`,
  66         `--ignore-space-at-eol`, and `--ignore-cr-at-eol`.
  67 +
  68 * If 'their' version only introduces whitespace changes to a line,
  69   'our' version is used;
  70 * If 'our' version introduces whitespace changes but 'their'
  71   version includes a substantial change, 'their' version is used;
  72 * Otherwise, the merge proceeds in the usual way.
  73
  74 renormalize;;
  75         This runs a virtual check-out and check-in of all three stages
  76         of a file when resolving a three-way merge.  This option is
  77         meant to be used when merging branches with different clean
  78         filters or end-of-line normalization rules.  See "Merging
  79         branches with differing checkin/checkout attributes" in
  80         linkgit:gitattributes[5] for details.
  81
  82 no-renormalize;;
  83         Disables the `renormalize` option.  This overrides the
  84         `merge.renormalize` configuration variable.
  85
  86 no-renames;;
  87         Turn off rename detection.
  88         See also linkgit:git-diff[1] `--no-renames`.
  89
  90 find-renames[=<n>];;
  91         Turn on rename detection, optionally setting the similarity
  92         threshold.  This is the default.
  93         See also linkgit:git-diff[1] `--find-renames`.
  94
  95 rename-threshold=<n>;;
  96         Deprecated synonym for `find-renames=<n>`.
  97
  98 subtree[=<path>];;
  99         This option is a more advanced form of 'subtree' strategy, where
 100         the strategy makes a guess on how two trees must be shifted to
 101         match with each other when merging.  Instead, the specified path
 102         is prefixed (or stripped from the beginning) to make the shape of
 103         two trees to match.
 104
 105 octopus::
 106         This resolves cases with more than two heads, but refuses to do
 107         a complex merge that needs manual resolution.  It is
 108         primarily meant to be used for bundling topic branch
 109         heads together.  This is the default merge strategy when
 110         pulling or merging more than one branch.
 111
 112 ours::
 113         This resolves any number of heads, but the resulting tree of the
 114         merge is always that of the current branch head, effectively
 115         ignoring all changes from all other branches.  It is meant to
 116         be used to supersede old development history of side
 117         branches.  Note that this is different from the -Xours option to
 118         the 'recursive' merge strategy.
 119
 120 subtree::
 121         This is a modified recursive strategy. When merging trees A and
 122         B, if B corresponds to a subtree of A, B is first adjusted to
 123         match the tree structure of A, instead of reading the trees at
 124         the same level. This adjustment is also done to the common
 125         ancestor tree.
 126
 127 With the strategies that use 3-way merge (including the default, 'recursive'),
 128 if a change is made on both branches, but later reverted on one of the
 129 branches, that change will be present in the merged result; some people find
 130 this behavior confusing.  It occurs because only the heads and the merge base
 131 are considered when performing a merge, not the individual commits.  The merge
 132 algorithm therefore considers the reverted change as no change at all, and
 133 substitutes the changed version instead.