Phases

Contents

Introduction
Available Phases
Phase Movements
command line interface
1. core command
2. impact on extension
Publishing Repository
Upgrade Notes

1. Introduction

The phase concept improves safety of history rewriting and control over changesets exchanged (read more). This phase concept aims to "just works" in a transparent manner for any user (read more). It is part of Core and always enabled in any new client but doesn't prevent older client to work on a repository (read more). Advanced user may decides to handle phase manually (read more).

Like bookmarks, phases are not stored in history and thus are not permanent and leave no audit trail.

This concept is introduced in Mercurial 2.1.

2. Available Phases

The phase concept allow to:

Prevent accidental rewriting part of the history expected to be immutable.
Keep immature changeset to be exchanged by mistake.

To achieve this, are three phases sharing a hierarchy of traits:

	immutable	shared
public	x	x
draft		x
secret

* The public phases holds changeset announced publicly in. They are expect to

always exists in your history and are said immutable. History rewriting extension will refuse to delete such immutable changeset. Every changeset your push or pull from a public server are set in this phase.

* The draft phase holds changesets that was not expect marked as part of

the permanent history. You can safely rewrite them. New commit are draft by default.

* The secret phase holds changeset that you do not want to exchange with

other repository. Secret changeset are hidden to remote peer and won't be included in push operation. Manual operation or Extension may turn changeset secret.

Phases split the history in coherent set of changeset. Every changeset in a phase have ancestor in a phase compatible with its phase. Compatible means an changeset ancestors have at least the same traits that the children changeset. eg: A shared changeset alway have shared ancestor and an immutable changeset always have immutable ancestors.

In other word the phase of a changeset is alway equal of higher that the phase of it's descendant. According to the following order:

public < draft < secret

A changeset is not expected to automatically move from a lower phase to an higher phase (eg: from public to draft) but automatic

3. Phase Movements

Phase movement are automatic and transparent and most user don't have to care much about them. The base rule is very simple:

“Any changesets on a remote repository is seen a public”

One standard exchange commands, the phase of changesets on both side are compared. If differ the lowest phase is choosed. (eg: a changeset known as draft locally but public remotely is set public localy. Because public < draft)

This update happen during standard exchange commands:

* pull: remote phase data are used to update the phase data on

the local repo. As pull is read only, it does not change changeset's phase on the remote

* push: remote phase data are used to the phase data on the local repo and

then local phase data are pushed to the local repo.

The real behavior is a it's a bit more complicated than changesets on a remote repository is seen a public, but this is true for repository keeping default . If you need a finer behavior, consult the publishing repository section.

New changeset committed locally are draft, but some extension like mq may create secret and handle the move from secret to draft automatically

Consult the #upgrade_Notes section to check how phase will move the first time a new version of Mercurial touch and existing repository.

4. command line interface

4.1. core command

4.2. impact on extension

5. Publishing Repository

By default any changeset exchanged over the wire are set public. Advanced user may want a finer behavior. The Publishing repository concept is designed for this purpose.

5.0.1. What is a "publishing repository"?

Setting a repository as "publishing" alter its behavior **when used as a server**: all changesets are **seen** as public changesets by clients.
So, pushing to a "publishing" repository is the most common way to make changesets public: pushed changesets are seen as public on the remote side and marked as such on local side.
Note: the "publishing" property have no effects for local operations.

5.0.2. Old repository are publishing

Phase is the first step of a series of features aiming at handling mutable history within mercurial. Old client do not support such feature and are unable to hold phase data. The safest solution is to consider as public any changeset going through an old client.
Moreover, most hosting solution will not support phase from the beginning. Having old clients seen as public repositories will not change their usage: public repositories where you push *immutable* public changesets *shared* with others.

5.0.3. Why is "publishing" the default?

We discussed above that any changeset from a non-phase aware repository should be seen as public. This means that in the following scenario, X is pulled as public::
~/A$ old-hg init
~/A$ echo 'babar' > jungle ~/A$ old-hg commit -mA 'X' ~/A$ cd ../B ~/B$ new-hg pull ../A # let's pretend A is served by old-hg ~/B$ new-hg log -r tip
summary: X phase: public
We want to keep this behavior while creating/serving the A repository with new-hg. Although committing with any new-hg creates a draft changeset. To stay backward compatible, the pull must see the new commit as public. Non-publishing server will advertise them as draft. Having publishing repository the default is thus necessary to ensure this backward compatibility.
This default value can also be expressed with the following sentence: "By default, without any configuration, everything you exchange with the outside is immutable.". This behaviour seems sane.

5.0.4. Why allow draft changeset in publishing repository

Note: The publish option is aimed at controlling the behavior of *server*. Changeset in any state on a publishing server will **always*** be seen as public by other client. "Passive" repository which are only used as server for pull and push operation are not "affected" by this section.
As in the choice for default, the main reason to allow draft changeset in publishing server is backward compatibility. With an old client, the following scenario is valid::
~/A$ old-hg init
~/A$ echo 'babar' > jungle ~/A$ old-hg commit -mA 'X' ~/A$ old-hg qimport -r . # or any other mutable operation on X
If the default is publishing and new commits in such repository are "public" The following operation will be denied as X will be an **immutable** public changeset. However as other clients see X as public, any pull//push (or event pull//pull) will mark X as public in repo A.
Allowing enforcement of public changeset only repository through config is probably something to do. This could be done with another "strict" option or a third value config for phase related option (mode=public, publishing(default), mutable)

6. Upgrade Notes

(If you were looking to the developer oriented page: PhaseDevel)