merge-strategies.txt

MERGE STRATEGIES
----------------

The merge mechanism (`git merge` and `git pull` commands) allows the
backend 'merge strategies' to be chosen with `-s` option. Some strategies
can also take their own options, which can be passed by giving `-X<option>`
arguments to `git merge` and/or `git pull`.

ort::
This is the default merge strategy when pulling or merging one
branch. This strategy can only resolve two heads using a
3-way merge algorithm. When there is more than one common
ancestor that can be used for 3-way merge, it creates a merged
tree of the common ancestors and uses that as the reference
tree for the 3-way merge. This has been reported to result in
fewer merge conflicts without causing mismerges by tests done
on actual merge commits taken from Linux 2.6 kernel
development history. Additionally this strategy can detect
and handle merges involving renames. It does not make use of
detected copies. The name for this algorithm is an acronym
("Ostensibly Recursive's Twin") and came from the fact that it
was written as a replacement for the previous default
algorithm, `recursive`.
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The 'ort' strategy can take the following options:

ours;;
This option forces conflicting hunks to be auto-resolved cleanly by
favoring 'our' version. Changes from the other tree that do not
conflict with our side are reflected in the merge result.
For a binary file, the entire contents are taken from our side.
+
This should not be confused with the 'ours' merge strategy, which does not
even look at what the other tree contains at all. It discards everything
the other tree did, declaring 'our' history contains all that happened in it.

theirs;;
This is the opposite of 'ours'; note that, unlike 'ours', there is
no 'theirs' merge strategy to confuse this merge option with.

ignore-space-change;;
ignore-all-space;;
ignore-space-at-eol;;
ignore-cr-at-eol;;
Treats lines with the indicated type of whitespace change as
unchanged for the sake of a three-way merge. Whitespace
changes mixed with other changes to a line are not ignored.
See also linkgit:git-diff[1] `-b`, `-w`,
`--ignore-space-at-eol`, and `--ignore-cr-at-eol`.
+
* If 'their' version only introduces whitespace changes to a line,
 'our' version is used;
* If 'our' version introduces whitespace changes but 'their'
 version includes a substantial change, 'their' version is used;
* Otherwise, the merge proceeds in the usual way.

renormalize;;
This runs a virtual check-out and check-in of all three stages
of a file when resolving a three-way merge. This option is
meant to be used when merging branches with different clean
filters or end-of-line normalization rules. See "Merging
branches with differing checkin/checkout attributes" in
linkgit:gitattributes[5] for details.

no-renormalize;;
Disables the `renormalize` option. This overrides the
`merge.renormalize` configuration variable.

find-renames[=<n>];;
Turn on rename detection, optionally setting the similarity
threshold. This is the default. This overrides the
'merge.renames' configuration variable.
See also linkgit:git-diff[1] `--find-renames`.

rename-threshold=<n>;;
Deprecated synonym for `find-renames=<n>`.

subtree[=<path>];;
This option is a more advanced form of 'subtree' strategy, where
the strategy makes a guess on how two trees must be shifted to
match with each other when merging. Instead, the specified path
is prefixed (or stripped from the beginning) to make the shape of
two trees to match.

recursive::
This can only resolve two heads using a 3-way merge
algorithm. When there is more than one common
ancestor that can be used for 3-way merge, it creates a
merged tree of the common ancestors and uses that as
the reference tree for the 3-way merge. This has been
reported to result in fewer merge conflicts without
causing mismerges by tests done on actual merge commits
taken from Linux 2.6 kernel development history.
Additionally this can detect and handle merges involving
renames. It does not make use of detected copies. This was
the default strategy for resolving two heads from Git v0.99.9k
until v2.33.0.
+
The 'recursive' strategy takes the same options as 'ort'. However,
there are three additional options that 'ort' ignores (not documented
above) that are potentially useful with the 'recursive' strategy:

patience;;
Deprecated synonym for `diff-algorithm=patience`.

diff-algorithm=[patience|minimal|histogram|myers];;
Use a different diff algorithm while merging, which can help
avoid mismerges that occur due to unimportant matching lines
(such as braces from distinct functions). See also
linkgit:git-diff[1] `--diff-algorithm`. Note that `ort`
specifically uses `diff-algorithm=histogram`, while `recursive`
defaults to the `diff.algorithm` config setting.

no-renames;;
Turn off rename detection. This overrides the `merge.renames`
configuration variable.
See also linkgit:git-diff[1] `--no-renames`.

resolve::
This can only resolve two heads (i.e. the current branch
and another branch you pulled from) using a 3-way merge
algorithm. It tries to carefully detect criss-cross
merge ambiguities. It does not handle renames.

octopus::
This resolves cases with more than two heads, but refuses to do
a complex merge that needs manual resolution. It is
primarily meant to be used for bundling topic branch
heads together. This is the default merge strategy when
pulling or merging more than one branch.

ours::
This resolves any number of heads, but the resulting tree of the
merge is always that of the current branch head, effectively
ignoring all changes from all other branches. It is meant to
be used to supersede old development history of side
branches. Note that this is different from the -Xours option to
the 'recursive' merge strategy.

subtree::
This is a modified `ort` strategy. When merging trees A and
B, if B corresponds to a subtree of A, B is first adjusted to
match the tree structure of A, instead of reading the trees at
the same level. This adjustment is also done to the common
ancestor tree.

With the strategies that use 3-way merge (including the default, 'ort'),
if a change is made on both branches, but later reverted on one of the
branches, that change will be present in the merged result; some people find
this behavior confusing. It occurs because only the heads and the merge base
are considered when performing a merge, not the individual commits. The merge
algorithm therefore considers the reverted change as no change at all, and
substitutes the changed version instead.