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| 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, but currently cannot make use of detected |
| 27 | + copies. This is the default merge strategy when pulling |
| 28 | + or merging one branch. |
| 29 | ++ |
| 30 | +The 'recursive' strategy can take the following options: |
| 31 | + |
| 32 | +ours;; |
| 33 | + This option forces conflicting hunks to be auto-resolved cleanly by |
| 34 | + favoring 'our' version. Changes from the other tree that do not |
| 35 | + conflict with our side are reflected to the merge result. |
| 36 | + For a binary file, the entire contents are taken from our side. |
| 37 | ++ |
| 38 | +This should not be confused with the 'ours' merge strategy, which does not |
| 39 | +even look at what the other tree contains at all. It discards everything |
| 40 | +the other tree did, declaring 'our' history contains all that happened in it. |
| 41 | + |
| 42 | +theirs;; |
| 43 | + This is the opposite of 'ours'; note that, unlike 'ours', there is |
| 44 | + no 'theirs' merge strategy to confuse this merge option with. |
| 45 | + |
| 46 | +patience;; |
| 47 | + With this option, 'merge-recursive' spends a little extra time |
| 48 | + to avoid mismerges that sometimes occur due to unimportant |
| 49 | + matching lines (e.g., braces from distinct functions). Use |
| 50 | + this when the branches to be merged have diverged wildly. |
| 51 | + See also linkgit:git-diff[1] `--patience`. |
| 52 | + |
| 53 | +diff-algorithm=[patience|minimal|histogram|myers];; |
| 54 | + Tells 'merge-recursive' to use a different diff algorithm, which |
| 55 | + can help avoid mismerges that occur due to unimportant matching |
| 56 | + lines (such as braces from distinct functions). See also |
| 57 | + linkgit:git-diff[1] `--diff-algorithm`. |
| 58 | + |
| 59 | +ignore-space-change;; |
| 60 | +ignore-all-space;; |
| 61 | +ignore-space-at-eol;; |
| 62 | +ignore-cr-at-eol;; |
| 63 | + Treats lines with the indicated type of whitespace change as |
| 64 | + unchanged for the sake of a three-way merge. Whitespace |
| 65 | + changes mixed with other changes to a line are not ignored. |
| 66 | + See also linkgit:git-diff[1] `-b`, `-w`, |
| 67 | + `--ignore-space-at-eol`, and `--ignore-cr-at-eol`. |
| 68 | ++ |
| 69 | +* If 'their' version only introduces whitespace changes to a line, |
| 70 | + 'our' version is used; |
| 71 | +* If 'our' version introduces whitespace changes but 'their' |
| 72 | + version includes a substantial change, 'their' version is used; |
| 73 | +* Otherwise, the merge proceeds in the usual way. |
| 74 | + |
| 75 | +renormalize;; |
| 76 | + This runs a virtual check-out and check-in of all three stages |
| 77 | + of a file when resolving a three-way merge. This option is |
| 78 | + meant to be used when merging branches with different clean |
| 79 | + filters or end-of-line normalization rules. See "Merging |
| 80 | + branches with differing checkin/checkout attributes" in |
| 81 | + linkgit:gitattributes[5] for details. |
| 82 | + |
| 83 | +no-renormalize;; |
| 84 | + Disables the `renormalize` option. This overrides the |
| 85 | + `merge.renormalize` configuration variable. |
| 86 | + |
| 87 | +no-renames;; |
| 88 | + Turn off rename detection. This overrides the `merge.renames` |
| 89 | + configuration variable. |
| 90 | + See also linkgit:git-diff[1] `--no-renames`. |
| 91 | + |
| 92 | +find-renames[=<n>];; |
| 93 | + Turn on rename detection, optionally setting the similarity |
| 94 | + threshold. This is the default. This overrides the |
| 95 | + 'merge.renames' configuration variable. |
| 96 | + See also linkgit:git-diff[1] `--find-renames`. |
| 97 | + |
| 98 | +rename-threshold=<n>;; |
| 99 | + Deprecated synonym for `find-renames=<n>`. |
| 100 | + |
| 101 | +subtree[=<path>];; |
| 102 | + This option is a more advanced form of 'subtree' strategy, where |
| 103 | + the strategy makes a guess on how two trees must be shifted to |
| 104 | + match with each other when merging. Instead, the specified path |
| 105 | + is prefixed (or stripped from the beginning) to make the shape of |
| 106 | + two trees to match. |
| 107 | + |
| 108 | +octopus:: |
| 109 | + This resolves cases with more than two heads, but refuses to do |
| 110 | + a complex merge that needs manual resolution. It is |
| 111 | + primarily meant to be used for bundling topic branch |
| 112 | + heads together. This is the default merge strategy when |
| 113 | + pulling or merging more than one branch. |
| 114 | + |
| 115 | +ours:: |
| 116 | + This resolves any number of heads, but the resulting tree of the |
| 117 | + merge is always that of the current branch head, effectively |
| 118 | + ignoring all changes from all other branches. It is meant to |
| 119 | + be used to supersede old development history of side |
| 120 | + branches. Note that this is different from the -Xours option to |
| 121 | + the 'recursive' merge strategy. |
| 122 | + |
| 123 | +subtree:: |
| 124 | + This is a modified recursive strategy. When merging trees A and |
| 125 | + B, if B corresponds to a subtree of A, B is first adjusted to |
| 126 | + match the tree structure of A, instead of reading the trees at |
| 127 | + the same level. This adjustment is also done to the common |
| 128 | + ancestor tree. |
| 129 | + |
| 130 | +With the strategies that use 3-way merge (including the default, 'recursive'), |
| 131 | +if a change is made on both branches, but later reverted on one of the |
| 132 | +branches, that change will be present in the merged result; some people find |
| 133 | +this behavior confusing. It occurs because only the heads and the merge base |
| 134 | +are considered when performing a merge, not the individual commits. The merge |
| 135 | +algorithm therefore considers the reverted change as no change at all, and |
| 136 | +substitutes the changed version instead. |
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