GIT-MERGE-TREE(1) Git Manual GIT-MERGE-TREE(1)
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:
o three way content merges of individual files
o rename detection
o proper directory/file conflict handling
o recursive ancestor consolidation (i.e. when there is more than one
merge base, creating a virtual merge base by merging the merge
bases)
o 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Do not quote filenames in the 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=<commit>
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.
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
o "Auto-merging"
o "CONFLICT (rename/delete)"
o "CONFLICT (submodule lacks merge base)"
o "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:
o "Auto-merging <file>"
o "CONFLICT (rename/delete): <oldfile> renamed...but deleted in..."
o "Failed to merge submodule <submodule> (no merge base)"
o "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):
o what would be written to the working tree (the OID of toplevel
tree)
o the higher order stages that would be written to the index (the
Conflicted file info)
o 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
Git 2.43.5 05/31/2024 GIT-MERGE-TREE(1)
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