mercurial/help/diffs.txt

flags: allow specifying --no-boolean-flag on the command line (BC)

This makes it much easier to enable some anti-foot-shooting features
(like update --check) by default, because now all boolean flags can be
explicitly disabled on the command line without having to use HGPLAIN
or similar. Flags which don't deserve this treatment can be removed
from consideration by adding them to the nevernegate set in fancyopts.

This doesn't make it any easier to identify when a flag is set: opts
still always gets filled in, either with the user-specified flag value
or with the default from the flags list in the command
table. Improving that would probably clean things up a bit, but for
now if you want a boolean flag and care if it was explicitly false or
default false (or true, but nobody uses that functionality because
before now it was nonsense) you need to use None as your default
rather than True or False.

This doesn't (yet) update help output, because I'm not quite sure how
to do that cleanly.

Mercurial's default format for showing changes between two versions of
a file is compatible with the unified format of GNU diff, which can be
used by GNU patch and many other standard tools.

While this standard format is often enough, it does not encode the
following information:

- executable status and other permission bits
- copy or rename information
- changes in binary files
- creation or deletion of empty files

Mercurial also supports the extended diff format from the git VCS
which addresses these limitations. The git diff format is not produced
by default because a few widespread tools still do not understand this
format.

This means that when generating diffs from a Mercurial repository
(e.g. with :hg:`export`), you should be careful about things like file
copies and renames or other things mentioned above, because when
applying a standard diff to a different repository, this extra
information is lost. Mercurial's internal operations (like push and
pull) are not affected by this, because they use an internal binary
format for communicating changes.

To make Mercurial produce the git extended diff format, use the --git
option available for many commands, or set 'git = True' in the [diff]
section of your configuration file. You do not need to set this option
when importing diffs in this format or using them in the mq extension.