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  44         Do not quote filenames in the 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