mercurial/help/diffs.txt

revert: apply normallookup on reverted file if size isn't changed (issue4583)

Before this patch, reverting a file to the revision other than the
parent doesn't update dirstate. This seems to expect that timestamp
and/or size will be changed by reverting.

But if (1) dirstate of file "f" is filled with timestamp before
reverting and (2) size and timestamp of file "f" isn't changed at
reverting, file "f" is recognized as CLEAN unexpectedly.

This patch applies "dirstate.normallookup()" on reverted file, if size
isn't changed.

Making "localrepository.wwrite()" return length of written data is
needed to avoid additional (and redundant) "lstat(2)" on the reverted
file. "filectx.size()" can't be used to know it, because data may be
decoded at being written out.

BTW, interactive reverting may cause similar problem, too. But this
patch doesn't focus on fixing it, because (1) interactive (maybe slow)
reverting changes one (or both) of size/timestamp of reverted files in
many usecases, and (2) changes to fix it seems not suitable for stable
branch.

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.