view mercurial/help/diffs.txt @ 40009:842ffcf1d42f

storageutil: extract most of emitrevisions() to standalone function

As part of implementing a storage backend, I found myself copying
most of revlog.emitrevisions(). This code is highly nuanced and it
bothered me greatly to be copying such low-level code.

This commit extracts the bulk of revlog.emitrevisions() into a
new standalone function. In order to make the function generally
usable, all "self" function calls that aren't exposed on the
ifilestorage interface are passed in via callable arguments.

No meaningful behavior should have changed as part of the port.

Upcoming commits will tweak behavior to make the code more
generically usable.

Differential Revision: https://phab.mercurial-scm.org/D4803

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.