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NAME
git-merge-tree - Perform merge without touching index or working tree
SYNOPSIS
git merge-tree [--write-tree] [<options>] <branch1> <branch2>
git merge-tree [--trivial-merge] <base-tree> <branch1> <branch2> (deprecated)
DESCRIPTION
This command has a modern --write-tree mode and a deprecated --trivial-merge mode. With
the exception of the DEPRECATED DESCRIPTION section at the end, the rest of this
documentation describes the modern --write-tree mode.
Performs a merge, but does not make any new commits and does not read from or write to
either the working tree or index.
The performed merge will use the same features as the "real" git-merge(1), including:
• three way content merges of individual files
• rename detection
• proper directory/file conflict handling
• recursive ancestor consolidation (i.e. when there is more than one merge base,
creating a virtual merge base by merging the merge bases)
• etc.
After the merge completes, a new toplevel tree object is created. See OUTPUT below for
details.
OPTIONS
-z
Do not quote filenames in the <Conflicted file info> section, and end each filename
with a NUL character rather than newline. Also begin the messages section with a NUL
character instead of a newline. See the section called “OUTPUT” below for more
information.
--name-only
In the Conflicted file info section, instead of writing a list of (mode, oid, stage,
path) tuples to output for conflicted files, just provide a list of filenames with
conflicts (and do not list filenames multiple times if they have multiple conflicting
stages).
--[no-]messages
Write any informational messages such as "Auto-merging <path>" or CONFLICT notices to
the end of stdout. If unspecified, the default is to include these messages if there
are merge conflicts, and to omit them otherwise.
--allow-unrelated-histories
merge-tree will by default error out if the two branches specified share no common
history. This flag can be given to override that check and make the merge proceed
anyway.
--merge-base=<tree-ish>
Instead of finding the merge-bases for <branch1> and <branch2>, specify a merge-base
for the merge, and specifying multiple bases is currently not supported. This option
is incompatible with --stdin.
As the merge-base is provided directly, <branch1> and <branch2> do not need to specify
commits; trees are enough.
OUTPUT
For a successful merge, the output from git-merge-tree is simply one line:
<OID of toplevel tree>
Whereas for a conflicted merge, the output is by default of the form:
<OID of toplevel tree>
<Conflicted file info>
<Informational messages>
These are discussed individually below.
However, there is an exception. If --stdin is passed, then there is an extra section at
the beginning, a NUL character at the end, and then all the sections repeat for each line
of input. Thus, if the first merge is conflicted and the second is clean, the output would
be of the form:
<Merge status>
<OID of toplevel tree>
<Conflicted file info>
<Informational messages>
NUL
<Merge status>
<OID of toplevel tree>
NUL
Merge status
This is an integer status followed by a NUL character. The integer status is:
0: merge had conflicts
1: merge was clean
<0: something prevented the merge from running (e.g. access to repository
objects denied by filesystem)
OID of toplevel tree
This is a tree object that represents what would be checked out in the working tree at the
end of git merge. If there were conflicts, then files within this tree may have embedded
conflict markers. This section is always followed by a newline (or NUL if -z is passed).
Conflicted file info
This is a sequence of lines with the format
<mode> <object> <stage> <filename>
The filename will be quoted as explained for the configuration variable core.quotePath
(see git-config(1)). However, if the --name-only option is passed, the mode, object, and
stage will be omitted. If -z is passed, the "lines" are terminated by a NUL character
instead of a newline character.
Informational messages
This section provides informational messages, typically about conflicts. The format of the
section varies significantly depending on whether -z is passed.
If -z is passed:
The output format is zero or more conflict informational records, each of the form:
<list-of-paths><conflict-type>NUL<conflict-message>NUL
where <list-of-paths> is of the form
<number-of-paths>NUL<path1>NUL<path2>NUL...<pathN>NUL
and includes paths (or branch names) affected by the conflict or informational message in
<conflict-message>. Also, <conflict-type> is a stable string explaining the type of
conflict, such as
• "Auto-merging"
• "CONFLICT (rename/delete)"
• "CONFLICT (submodule lacks merge base)"
• "CONFLICT (binary)"
and <conflict-message> is a more detailed message about the conflict which often (but not
always) embeds the <stable-short-type-description> within it. These strings may change in
future Git versions. Some examples:
• "Auto-merging <file>"
• "CONFLICT (rename/delete): <oldfile> renamed...but deleted in..."
• "Failed to merge submodule <submodule> (no merge base)"
• "Warning: cannot merge binary files: <filename>"
If -z is NOT passed:
This section starts with a blank line to separate it from the previous sections, and then
only contains the <conflict-message> information from the previous section (separated by
newlines). These are non-stable strings that should not be parsed by scripts, and are just
meant for human consumption. Also, note that while <conflict-message> strings usually do
not contain embedded newlines, they sometimes do. (However, the free-form messages will
never have an embedded NUL character). So, the entire block of information is meant for
human readers as an agglomeration of all conflict messages.
EXIT STATUS
For a successful, non-conflicted merge, the exit status is 0. When the merge has
conflicts, the exit status is 1. If the merge is not able to complete (or start) due to
some kind of error, the exit status is something other than 0 or 1 (and the output is
unspecified). When --stdin is passed, the return status is 0 for both successful and
conflicted merges, and something other than 0 or 1 if it cannot complete all the requested
merges.
USAGE NOTES
This command is intended as low-level plumbing, similar to git-hash-object(1), git-
mktree(1), git-commit-tree(1), git-write-tree(1), git-update-ref(1), and git-mktag(1).
Thus, it can be used as a part of a series of steps such as:
NEWTREE=$(git merge-tree --write-tree $BRANCH1 $BRANCH2)
test $? -eq 0 || die "There were conflicts..."
NEWCOMMIT=$(git commit-tree $NEWTREE -p $BRANCH1 -p $BRANCH2)
git update-ref $BRANCH1 $NEWCOMMIT
Note that when the exit status is non-zero, NEWTREE in this sequence will contain a lot
more output than just a tree.
For conflicts, the output includes the same information that you’d get with git-merge(1):
• what would be written to the working tree (the OID of toplevel tree)
• the higher order stages that would be written to the index (the Conflicted file info)
• any messages that would have been printed to stdout (the Informational messages)
INPUT FORMAT
git merge-tree --stdin input format is fully text based. Each line has this format:
[<base-commit> -- ]<branch1> <branch2>
If one line is separated by --, the string before the separator is used for specifying a
merge-base for the merge and the string after the separator describes the branches to be
merged.
MISTAKES TO AVOID
Do NOT look through the resulting toplevel tree to try to find which files conflict; parse
the Conflicted file info section instead. Not only would parsing an entire tree be
horrendously slow in large repositories, there are numerous types of conflicts not
representable by conflict markers (modify/delete, mode conflict, binary file changed on
both sides, file/directory conflicts, various rename conflict permutations, etc.)
Do NOT interpret an empty Conflicted file info list as a clean merge; check the exit
status. A merge can have conflicts without having individual files conflict (there are a
few types of directory rename conflicts that fall into this category, and others might
also be added in the future).
Do NOT attempt to guess or make the user guess the conflict types from the Conflicted file
info list. The information there is insufficient to do so. For example:
Rename/rename(1to2) conflicts (both sides renamed the same file differently) will result
in three different files having higher order stages (but each only has one higher order
stage), with no way (short of the Informational messages section) to determine which three
files are related. File/directory conflicts also result in a file with exactly one higher
order stage. Possibly-involved-in-directory-rename conflicts (when
"merge.directoryRenames" is unset or set to "conflicts") also result in a file with
exactly one higher order stage. In all cases, the Informational messages section has the
necessary info, though it is not designed to be machine parseable.
Do NOT assume that each path from Conflicted file info, and the logical conflicts in the
Informational messages have a one-to-one mapping, nor that there is a one-to-many mapping,
nor a many-to-one mapping. Many-to-many mappings exist, meaning that each path can have
many logical conflict types in a single merge, and each logical conflict type can affect
many paths.
Do NOT assume all filenames listed in the Informational messages section had conflicts.
Messages can be included for files that have no conflicts, such as "Auto-merging <file>".
AVOID taking the OIDS from the Conflicted file info and re-merging them to present the
conflicts to the user. This will lose information. Instead, look up the version of the
file found within the OID of toplevel tree and show that instead. In particular, the
latter will have conflict markers annotated with the original branch/commit being merged
and, if renames were involved, the original filename. While you could include the original
branch/commit in the conflict marker annotations when re-merging, the original filename is
not available from the Conflicted file info and thus you would be losing information that
might help the user resolve the conflict.
DEPRECATED DESCRIPTION
Per the DESCRIPTION and unlike the rest of this documentation, this section describes the
deprecated --trivial-merge mode.
Other than the optional --trivial-merge, this mode accepts no options.
This mode reads three tree-ish, and outputs trivial merge results and conflicting stages
to the standard output in a semi-diff format. Since this was designed for higher level
scripts to consume and merge the results back into the index, it omits entries that match
<branch1>. The result of this second form is similar to what three-way git read-tree -m
does, but instead of storing the results in the index, the command outputs the entries to
the standard output.
This form not only has limited applicability (a trivial merge cannot handle content merges
of individual files, rename detection, proper directory/file conflict handling, etc.), the
output format is also difficult to work with, and it will generally be less performant
than the first form even on successful merges (especially if working in large
repositories).
GIT
Part of the git(1) suite