view mercurial/help/internals/requirements.txt @ 33556:22371eabb3b1

sparse: add a requirement when a repository uses sparse (BC)

The presence of a sparse checkout can confuse legacy clients or
clients without sparse enabled for reasons that should be obvious.

This commit introduces a new repository requirement that tracks
whether sparse is enabled. The requirement is added when a sparse
config is activated and removed when the sparse config is reset.

The localrepository constructor has been taught to not open repos
with this requirement unless the sparse feature is enabled. It yields
a more actionable error message than what you would get if the
lockout were handled strictly at the requirements verification phase.
Old clients that aren't sparse aware will see the generic
"repository requires features unknown to this Mercurial" error,
however.

The new requirement has "exp" in its name to reflect the
experimental nature of sparse. There's a chance that the eventual
non-experimental feature won't change significantly and we could
have squatted on the "sparse" requirement without ill effect. If
that happens, we can teach new clients to still recognize the old
name. But I suspect we'll sneak in some BC and we'll want a new
requirement to convey new meaning.

Differential Revision: https://phab.mercurial-scm.org/D110

Repositories contain a file (``.hg/requires``) containing a list of
features/capabilities that are *required* for clients to interface
with the repository. This file has been present in Mercurial since
version 0.9.2 (released December 2006).

One of the first things clients do when opening a repository is read
``.hg/requires`` and verify that all listed requirements are supported,
aborting if not. Requirements are therefore a strong mechanism to
prevent incompatible clients from reading from unknown repository
formats or even corrupting them by writing to them.

Extensions may add requirements. When they do this, clients not running
an extension will be unable to read from repositories.

The following sections describe the requirements defined by the
Mercurial core distribution.

revlogv1
========

When present, revlogs are version 1 (RevlogNG). RevlogNG was introduced
in 2006. The ``revlogv1`` requirement has been enabled by default
since the ``requires`` file was introduced in Mercurial 0.9.2.

If this requirement is not present, version 0 revlogs are assumed.

store
=====

The *store* repository layout should be used.

This requirement has been enabled by default since the ``requires`` file
was introduced in Mercurial 0.9.2.

fncache
=======

The *fncache* repository layout should be used.

The *fncache* layout hash encodes filenames with long paths and
encodes reserved filenames.

This requirement is enabled by default when the *store* requirement is
enabled (which is the default behavior). It was introduced in Mercurial
1.1 (released December 2008).

shared
======

Denotes that the store for a repository is shared from another location
(defined by the ``.hg/sharedpath`` file).

This requirement is set when a repository is created via :hg:`share`.

The requirement was added in Mercurial 1.3 (released July 2009).

relshared
=========

Derivative of ``shared``; the location of the store is relative to the
store of this repository.

This requirement is set when a repository is created via :hg:`share`
using the ``--relative`` option.

The requirement was added in Mercurial 4.2 (released May 2017).

dotencode
=========

The *dotencode* repository layout should be used.

The *dotencode* layout encodes the first period or space in filenames
to prevent issues on OS X and Windows.

This requirement is enabled by default when the *store* requirement
is enabled (which is the default behavior). It was introduced in
Mercurial 1.7 (released November 2010).

parentdelta
===========

Denotes a revlog delta encoding format that was experimental and
replaced by *generaldelta*. It should not be seen in the wild because
it was never enabled by default.

This requirement was added in Mercurial 1.7 and removed in Mercurial
1.9.

generaldelta
============

Revlogs should be created with the *generaldelta* flag enabled. The
generaldelta flag will cause deltas to be encoded against a parent
revision instead of the previous revision in the revlog.

Support for this requirement was added in Mercurial 1.9 (released
July 2011). The requirement was disabled on new repositories by
default until Mercurial 3.7 (released February 2016).

manifestv2
==========

Denotes that version 2 of manifests are being used.

Support for this requirement was added in Mercurial 3.4 (released
May 2015). The requirement is currently experimental and is disabled
by default.

treemanifest
============

Denotes that tree manifests are being used. Tree manifests are
one manifest per directory (as opposed to a single flat manifest).

Support for this requirement was added in Mercurial 3.4 (released
August 2015). The requirement is currently experimental and is
disabled by default.

exp-sparse
==========

The working directory is sparse (only contains a subset of files).

Support for this requirement was added in Mercurial 4.3 (released
August 2017). This requirement and feature are experimental and may
disappear in a future Mercurial release. The requirement will only
be present on repositories that have opted in to a sparse working
directory.