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diff --git a/Documentation/git-merge-tree.txt b/Documentation/git-merge-tree.txt index 58731c1..dd388fa 100644 --- a/Documentation/git-merge-tree.txt +++ b/Documentation/git-merge-tree.txt @@ -3,26 +3,316 @@ git-merge-tree(1) NAME ---- -git-merge-tree - Show three-way merge without touching index +git-merge-tree - Perform merge without touching index or working tree SYNOPSIS -------- [verse] -'git merge-tree' <base-tree> <branch1> <branch2> +'git merge-tree' [--write-tree] [<options>] <branch1> <branch2> +'git merge-tree' [--trivial-merge] <base-tree> <branch1> <branch2> (deprecated) +[[NEWMERGE]] DESCRIPTION ----------- -Reads three tree-ish, and output trivial merge results and -conflicting stages to the standard output. This 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 is meant to be used by higher level scripts to compute -merge results outside of the index, and stuff the results back into the -index. For this reason, the output from the command omits -entries that match the <branch1> tree. + +This command has a modern `--write-tree` mode and a deprecated +`--trivial-merge` mode. With the exception of the +<<DEPMERGE,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" +linkgit: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 + +OPTIONS +------- + +-z:: + Do not quote filenames in the 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 <<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]] +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 + +[[MS]] +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) + +[[OIDTLT]] +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). + +[[CFI]] +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 linkgit: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. + +[[IM]] +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 +linkgit:git-hash-object[1], linkgit:git-mktree[1], +linkgit:git-commit-tree[1], linkgit:git-write-tree[1], +linkgit:git-update-ref[1], and linkgit: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 linkgit:git-merge[1]: + + * what would be written to the working tree (the + <<OIDTLT,OID of toplevel tree>>) + * the higher order stages that would be written to the index (the + <<CFI,Conflicted file info>>) + * any messages that would have been printed to stdout (the + <<IM,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 <<CFI,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 <<CFI,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 <<CFI,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 <<IM,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 +<<IM,Informational messages>> section has the necessary info, though it +is not designed to be machine parseable. + +Do NOT assume that each path from <<CFI,Conflicted file info>>, and +the logical conflicts in the <<IM,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 <<IM,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 <<CFI,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 +<<OIDTLT,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 <<CFI,Conflicted file info>> and thus you would +be losing information that might help the user resolve the conflict. + +[[DEPMERGE]] +DEPRECATED DESCRIPTION +---------------------- + +Per the <<NEWMERGE,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 --- |