view mercurial/help/merge-tools.txt @ 34391:6797f1fbc642

hgweb: add HTML elements to control whitespace settings for annotate

Building on top of the new URL query string arguments to control
whitespace settings for annotate, this commit adds HTML checkboxes
reflecting the values of these arguments to the paper and gitweb
themes.

The actual diff settings are now exported to the templating layer.
The HTML templates add these as data-* attributes so they are
accessible to the DOM.

A new <form> with various <input> elements is added. The <form>
is initially hidden via CSS. A shared JavaScript function (which
runs after the <form> has been rendered but before the annotate
HTML (because annotate HTML could take a while to load and we want
the form to render quickly) takes care of setting the checked state
of each box from the data-* attributes. It also registers an event
handler to modify the URL and refresh the page whenever the checkbox
state is changed.

I'm using the URLSearchParams interface to perform URL manipulation.
https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams tells
me this may not be supported on older web browsers. Yes, apparently
the web API didn't have a standard API to parse and format query
strings until recently. Hence the check for the presence of this
feature in the JavaScript. If the browser doesn't support the
feature, the <form> will remain hidden and behavior will like it
currently is. We could polyfill this feature or implement our own
query string parsing. But I'm lazy and this could be done as a
follow-up if people miss it.

We could certainly expand this feature to support more diff options
(such as lines of context). That's why the potentially reusable code
is stored in a reusable place. It is also certainly possible to
add diff controls to other pages that display diffs. But since
Mozillians are making noise about controlling which revisions
annotate shows, I figured I'd start there.

.. feature::

   Control whitespace settings for annotation on hgweb

   /annotate URLs on hgweb now accept query string arguments to
   influence how whitespace changes impact results.

   The arguments "ignorews," "ignorewsamount," "ignorewseol," and
   "ignoreblanklines" now have the same meaning as their [annotate]
   config section counterparts. Any provided setting overrides the
   server default.

   HTML checkboxes have been added to the paper and gitweb themes
   to expose current whitespace settings and to easily modify the
   current view.

Differential Revision: https://phab.mercurial-scm.org/D850

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 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.