Merge Tools

    To merge files Mercurial uses merge tools.

    A merge tool combines two different versions of a file into a merged file.
    Merge tools are given the two files and the greatest common ancestor of
    the two file versions, so they can determine the changes made on both

    Merge tools are used both for "hg resolve", "hg merge", "hg update", "hg
    backout" and in several extensions.

    Usually, the merge tool tries to automatically reconcile the files by
    combining all non-overlapping changes that occurred separately in the two
    different evolutions of the same initial base file. Furthermore, some
    interactive merge programs make it easier to manually resolve conflicting
    merges, either in a graphical way, or by inserting some conflict markers.
    Mercurial does not include any interactive merge programs but relies on
    external tools for that.

    Available merge tools

    External merge tools and their properties are configured in the merge-
    tools configuration section - see hgrc(5) - but they can often just be
    named by their executable.

    A merge tool is generally usable if its executable can be found on the
    system and if it can handle the merge. The executable is found if it is an
    absolute or relative executable path or the name of an application in the
    executable search path. The tool is assumed to be able to handle the merge
    if it can handle symlinks if the file is a symlink, if it can handle
    binary files if the file is binary, and if a GUI is available if the tool
    requires a GUI.

    There are some internal merge tools which can be used. The internal merge
    tools are:

      Creates three versions of the files to merge, containing the contents of
      local, other and base. These files can then be used to perform a merge
      manually. If the file to be merged is named "a.txt", these files will
      accordingly be named "a.txt.local", "a.txt.other" and "a.txt.base" and
      they will be placed in the same directory as "a.txt".

      Rather than attempting to merge files that were modified on both
      branches, it marks them as unresolved. The resolve command must be used
      to resolve these conflicts.

      Uses the local version of files as the merged version.

      Uses the internal non-interactive simple merge algorithm for merging
      files. It will fail if there are any conflicts and leave markers in the
      partially merged file.

      Uses the other version of files as the merged version.

      Asks the user which of the local or the other version to keep as the
      merged version.

    Internal tools are always available and do not require a GUI but will by
    default not handle symlinks or binary files.

    Choosing a merge tool

    Mercurial uses these rules when deciding which merge tool to use:

    1. If a tool has been specified with the --tool option to merge or
       resolve, it is used.  If it is the name of a tool in the merge-tools
       configuration, its configuration is used. Otherwise the specified tool
       must be executable by the shell.
    2. If the "HGMERGE" environment variable is present, its value is used and
       must be executable by the shell.
    3. If the filename of the file to be merged matches any of the patterns in
       the merge-patterns configuration section, the first usable merge tool
       corresponding to a matching pattern is used. Here, binary capabilities
       of the merge tool are not considered.
    4. If ui.merge is set it will be considered next. If the value is not the
       name of a configured tool, the specified value is used and must be
       executable by the shell. Otherwise the named tool is used if it is
    5. If any usable merge tools are present in the merge-tools configuration
       section, the one with the highest priority is used.
    6. If a program named "hgmerge" can be found on the system, it is used -
       but it will by default not be used for symlinks and binary files.
    7. If the file to be merged is not binary and is not a symlink, then
       "internal:merge" is used.
    8. The merge of the file fails and must be resolved before commit.

       After selecting a merge program, Mercurial will by default attempt to
       merge the files using a simple merge algorithm first. Only if it
       doesn't succeed because of conflicting changes Mercurial will actually
       execute the merge program. Whether to use the simple merge algorithm
       first can be controlled by the premerge setting of the merge tool.
       Premerge is enabled by default unless the file is binary or a symlink.

    See the merge-tools and ui sections of hgrc(5) for details on the
    configuration of merge tools.