Documentation/git-merge-tree.txt

   1 git-merge-tree(1)
   2 =================
   3
   4 NAME
   5 ----
   6 git-merge-tree - Perform merge without touching index or working tree
   7
   8
   9 SYNOPSIS
  10 --------
  11 [verse]
  12 'git merge-tree' [--write-tree] [<options>] <branch1> <branch2>
  13 'git merge-tree' [--trivial-merge] <base-tree> <branch1> <branch2> (deprecated)
  14
  15 [[NEWMERGE]]
  16 DESCRIPTION
  17 -----------
  18
  19 This command has a modern `--write-tree` mode and a deprecated
  20 `--trivial-merge` mode.  With the exception of the
  21 <<DEPMERGE,DEPRECATED DESCRIPTION>> section at the end, the rest of
  22 this documentation describes the modern `--write-tree` mode.
  23
  24 Performs a merge, but does not make any new commits and does not read
  25 from or write to either the working tree or index.
  26
  27 The performed merge will use the same features as the "real"
  28 linkgit:git-merge[1], including:
  29
  30   * three way content merges of individual files
  31   * rename detection
  32   * proper directory/file conflict handling
  33   * recursive ancestor consolidation (i.e. when there is more than one
  34     merge base, creating a virtual merge base by merging the merge bases)
  35   * etc.
  36
  37 After the merge completes, a new toplevel tree object is created.  See
  38 `OUTPUT` below for details.
  39
  40 OPTIONS
  41 -------
  42
  43 -z::
  44         Do not quote filenames in the <Conflicted file info> section,
  45         and end each filename with a NUL character rather than
  46         newline.  Also begin the messages section with a NUL character
  47         instead of a newline.  See <<OUTPUT>> below for more information.
  48
  49 --name-only::
  50         In the Conflicted file info section, instead of writing a list
  51         of (mode, oid, stage, path) tuples to output for conflicted
  52         files, just provide a list of filenames with conflicts (and
  53         do not list filenames multiple times if they have multiple
  54         conflicting stages).
  55
  56 --[no-]messages::
  57         Write any informational messages such as "Auto-merging <path>"
  58         or CONFLICT notices to the end of stdout.  If unspecified, the
  59         default is to include these messages if there are merge
  60         conflicts, and to omit them otherwise.
  61
  62 --allow-unrelated-histories::
  63         merge-tree will by default error out if the two branches specified
  64         share no common history.  This flag can be given to override that
  65         check and make the merge proceed anyway.
  66
  67 --merge-base=<tree-ish>::
  68         Instead of finding the merge-bases for <branch1> and <branch2>,
  69         specify a merge-base for the merge, and specifying multiple bases is
  70         currently not supported. This option is incompatible with `--stdin`.
  71 +
  72 As the merge-base is provided directly, <branch1> and <branch2> do not need
  73 to specify commits; trees are enough.
  74
  75 [[OUTPUT]]
  76 OUTPUT
  77 ------
  78
  79 For a successful merge, the output from git-merge-tree is simply one
  80 line:
  81
  82         <OID of toplevel tree>
  83
  84 Whereas for a conflicted merge, the output is by default of the form:
  85
  86         <OID of toplevel tree>
  87         <Conflicted file info>
  88         <Informational messages>
  89
  90 These are discussed individually below.
  91
  92 However, there is an exception.  If `--stdin` is passed, then there is
  93 an extra section at the beginning, a NUL character at the end, and then
  94 all the sections repeat for each line of input.  Thus, if the first merge
  95 is conflicted and the second is clean, the output would be of the form:
  96
  97         <Merge status>
  98         <OID of toplevel tree>
  99         <Conflicted file info>
 100         <Informational messages>
 101         NUL
 102         <Merge status>
 103         <OID of toplevel tree>
 104         NUL
 105
 106 [[MS]]
 107 Merge status
 108 ~~~~~~~~~~~~
 109
 110 This is an integer status followed by a NUL character.  The integer status is:
 111
 112      0: merge had conflicts
 113      1: merge was clean
 114      <0: something prevented the merge from running (e.g. access to repository
 115          objects denied by filesystem)
 116
 117 [[OIDTLT]]
 118 OID of toplevel tree
 119 ~~~~~~~~~~~~~~~~~~~~
 120
 121 This is a tree object that represents what would be checked out in the
 122 working tree at the end of `git merge`.  If there were conflicts, then
 123 files within this tree may have embedded conflict markers.  This section
 124 is always followed by a newline (or NUL if `-z` is passed).
 125
 126 [[CFI]]
 127 Conflicted file info
 128 ~~~~~~~~~~~~~~~~~~~~
 129
 130 This is a sequence of lines with the format
 131
 132         <mode> <object> <stage> <filename>
 133
 134 The filename will be quoted as explained for the configuration
 135 variable `core.quotePath` (see linkgit:git-config[1]).  However, if
 136 the `--name-only` option is passed, the mode, object, and stage will
 137 be omitted.  If `-z` is passed, the "lines" are terminated by a NUL
 138 character instead of a newline character.
 139
 140 [[IM]]
 141 Informational messages
 142 ~~~~~~~~~~~~~~~~~~~~~~
 143
 144 This section provides informational messages, typically about
 145 conflicts.  The format of the section varies significantly depending
 146 on whether `-z` is passed.
 147
 148 If `-z` is passed:
 149
 150 The output format is zero or more conflict informational records, each
 151 of the form:
 152
 153         <list-of-paths><conflict-type>NUL<conflict-message>NUL
 154
 155 where <list-of-paths> is of the form
 156
 157         <number-of-paths>NUL<path1>NUL<path2>NUL...<pathN>NUL
 158
 159 and includes paths (or branch names) affected by the conflict or
 160 informational message in <conflict-message>.  Also, <conflict-type> is a
 161 stable string explaining the type of conflict, such as
 162
 163   * "Auto-merging"
 164   * "CONFLICT (rename/delete)"
 165   * "CONFLICT (submodule lacks merge base)"
 166   * "CONFLICT (binary)"
 167
 168 and <conflict-message> is a more detailed message about the conflict which often
 169 (but not always) embeds the <stable-short-type-description> within it.  These
 170 strings may change in future Git versions.  Some examples:
 171
 172   * "Auto-merging <file>"
 173   * "CONFLICT (rename/delete): <oldfile> renamed...but deleted in..."
 174   * "Failed to merge submodule <submodule> (no merge base)"
 175   * "Warning: cannot merge binary files: <filename>"
 176
 177 If `-z` is NOT passed:
 178
 179 This section starts with a blank line to separate it from the previous
 180 sections, and then only contains the <conflict-message> information
 181 from the previous section (separated by newlines).  These are
 182 non-stable strings that should not be parsed by scripts, and are just
 183 meant for human consumption.  Also, note that while <conflict-message>
 184 strings usually do not contain embedded newlines, they sometimes do.
 185 (However, the free-form messages will never have an embedded NUL
 186 character).  So, the entire block of information is meant for human
 187 readers as an agglomeration of all conflict messages.
 188
 189 EXIT STATUS
 190 -----------
 191
 192 For a successful, non-conflicted merge, the exit status is 0.  When the
 193 merge has conflicts, the exit status is 1.  If the merge is not able to
 194 complete (or start) due to some kind of error, the exit status is
 195 something other than 0 or 1 (and the output is unspecified).  When
 196 --stdin is passed, the return status is 0 for both successful and
 197 conflicted merges, and something other than 0 or 1 if it cannot complete
 198 all the requested merges.
 199
 200 USAGE NOTES
 201 -----------
 202
 203 This command is intended as low-level plumbing, similar to
 204 linkgit:git-hash-object[1], linkgit:git-mktree[1],
 205 linkgit:git-commit-tree[1], linkgit:git-write-tree[1],
 206 linkgit:git-update-ref[1], and linkgit:git-mktag[1].  Thus, it can be
 207 used as a part of a series of steps such as:
 208
 209        NEWTREE=$(git merge-tree --write-tree $BRANCH1 $BRANCH2)
 210        test $? -eq 0 || die "There were conflicts..."
 211        NEWCOMMIT=$(git commit-tree $NEWTREE -p $BRANCH1 -p $BRANCH2)
 212        git update-ref $BRANCH1 $NEWCOMMIT
 213
 214 Note that when the exit status is non-zero, `NEWTREE` in this sequence
 215 will contain a lot more output than just a tree.
 216
 217 For conflicts, the output includes the same information that you'd get
 218 with linkgit:git-merge[1]:
 219
 220   * what would be written to the working tree (the
 221     <<OIDTLT,OID of toplevel tree>>)
 222   * the higher order stages that would be written to the index (the
 223     <<CFI,Conflicted file info>>)
 224   * any messages that would have been printed to stdout (the
 225     <<IM,Informational messages>>)
 226
 227 INPUT FORMAT
 228 ------------
 229 'git merge-tree --stdin' input format is fully text based. Each line
 230 has this format:
 231
 232         [<base-commit> -- ]<branch1> <branch2>
 233
 234 If one line is separated by `--`, the string before the separator is
 235 used for specifying a merge-base for the merge and the string after
 236 the separator describes the branches to be merged.
 237
 238 MISTAKES TO AVOID
 239 -----------------
 240
 241 Do NOT look through the resulting toplevel tree to try to find which
 242 files conflict; parse the <<CFI,Conflicted file info>> section instead.
 243 Not only would parsing an entire tree be horrendously slow in large
 244 repositories, there are numerous types of conflicts not representable by
 245 conflict markers (modify/delete, mode conflict, binary file changed on
 246 both sides, file/directory conflicts, various rename conflict
 247 permutations, etc.)
 248
 249 Do NOT interpret an empty <<CFI,Conflicted file info>> list as a clean
 250 merge; check the exit status.  A merge can have conflicts without having
 251 individual files conflict (there are a few types of directory rename
 252 conflicts that fall into this category, and others might also be added
 253 in the future).
 254
 255 Do NOT attempt to guess or make the user guess the conflict types from
 256 the <<CFI,Conflicted file info>> list.  The information there is
 257 insufficient to do so.  For example: Rename/rename(1to2) conflicts (both
 258 sides renamed the same file differently) will result in three different
 259 files having higher order stages (but each only has one higher order
 260 stage), with no way (short of the <<IM,Informational messages>> section)
 261 to determine which three files are related.  File/directory conflicts
 262 also result in a file with exactly one higher order stage.
 263 Possibly-involved-in-directory-rename conflicts (when
 264 "merge.directoryRenames" is unset or set to "conflicts") also result in
 265 a file with exactly one higher order stage.  In all cases, the
 266 <<IM,Informational messages>> section has the necessary info, though it
 267 is not designed to be machine parseable.
 268
 269 Do NOT assume that each path from <<CFI,Conflicted file info>>, and
 270 the logical conflicts in the <<IM,Informational messages>> have a
 271 one-to-one mapping, nor that there is a one-to-many mapping, nor a
 272 many-to-one mapping.  Many-to-many mappings exist, meaning that each
 273 path can have many logical conflict types in a single merge, and each
 274 logical conflict type can affect many paths.
 275
 276 Do NOT assume all filenames listed in the <<IM,Informational messages>>
 277 section had conflicts.  Messages can be included for files that have no
 278 conflicts, such as "Auto-merging <file>".
 279
 280 AVOID taking the OIDS from the <<CFI,Conflicted file info>> and
 281 re-merging them to present the conflicts to the user.  This will lose
 282 information.  Instead, look up the version of the file found within the
 283 <<OIDTLT,OID of toplevel tree>> and show that instead.  In particular,
 284 the latter will have conflict markers annotated with the original
 285 branch/commit being merged and, if renames were involved, the original
 286 filename.  While you could include the original branch/commit in the
 287 conflict marker annotations when re-merging, the original filename is
 288 not available from the <<CFI,Conflicted file info>> and thus you would
 289 be losing information that might help the user resolve the conflict.
 290
 291 [[DEPMERGE]]
 292 DEPRECATED DESCRIPTION
 293 ----------------------
 294
 295 Per the <<NEWMERGE,DESCRIPTION>> and unlike the rest of this
 296 documentation, this section describes the deprecated `--trivial-merge`
 297 mode.
 298
 299 Other than the optional `--trivial-merge`, this mode accepts no
 300 options.
 301
 302 This mode reads three tree-ish, and outputs trivial merge results and
 303 conflicting stages to the standard output in a semi-diff format.
 304 Since this was designed for higher level scripts to consume and merge
 305 the results back into the index, it omits entries that match
 306 <branch1>.  The result of this second form is similar to what
 307 three-way 'git read-tree -m' does, but instead of storing the results
 308 in the index, the command outputs the entries to the standard output.
 309
 310 This form not only has limited applicability (a trivial merge cannot
 311 handle content merges of individual files, rename detection, proper
 312 directory/file conflict handling, etc.), the output format is also
 313 difficult to work with, and it will generally be less performant than
 314 the first form even on successful merges (especially if working in
 315 large repositories).
 316
 317 GIT
 318 ---
 319 Part of the linkgit:git[1] suite