view mercurial/help/merge-tools.txt @ 37290:cc5a040fe150

wireproto: syntax for encoding CBOR into frames

We just vendored a library for encoding and decoding the CBOR
data format. While the intent of that vendor was to support state
files, CBOR is really a nice data format. It is extensible and
compact.

I've been feeling dirty inventing my own data formats for
frame payloads. While custom formats can always beat out a generic
format, there is a cost to be paid in terms of implementation,
comprehension, etc. CBOR is compact enough that I'm not too
worried about efficiency loss. I think the benefits of using
a standardized format outweigh rolling our own formats. So
I plan to make heavy use of CBOR in the wire protocol going
forward.

This commit introduces support for encoding CBOR data in frame
payloads to our function to make a frame from a human string.
We do need to employ some low-level Python code in order to
evaluate a string as a Python expression. But other than that,
this should hopefully be pretty straightforward.

Unit tests for this function have been added.

Differential Revision: https://phab.mercurial-scm.org/D2948

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 branches.

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:

.. internaltoolsmarker

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 usable.

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. Otherwise, ``:prompt`` is used.

.. note::

   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 will Mercurial 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.