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`.

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 and is considered generally safe and
	fast.

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.  This is the default merge strategy when
	pulling or merging one branch.
+
The 'recursive' 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 to 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'.

patience;;
	With this option, 'merge-recursive' spends a little extra time
	to avoid mismerges that sometimes occur due to unimportant
	matching lines (e.g., braces from distinct functions).  Use
	this when the branches to be merged have diverged wildly.
	See also linkgit:git-diff[1] `--patience`.

diff-algorithm=[patience|minimal|histogram|myers];;
	Tells 'merge-recursive' to use a different diff algorithm, 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`.

ignore-space-change;;
ignore-all-space;;
ignore-space-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`, and
	`--ignore-space-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.

rename-threshold=<n>;;
	Controls the similarity threshold used for rename detection.
	See also linkgit:git-diff[1] `-M`.

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.

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 recursive 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, 'recursive'),
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.