annotate docs/obs-terms.rst @ 1067:5d063fed9e3d

evolve: yield to relevant markers handling in core

The handling of obsolescence marker is now performed in core. If we detect a
mercurial with such power we skip the wrapping from evolve.

This changeset also suffer from massive diff from the change in display of
obsolescence marker with parent information introduced at the same time in core.

.. Copyright 2011 Pierre-Yves David <[e-mail]>
..                Logilab SA        <[e-mail]>

-----------------------------------------------------------
Terminology of the obsolete concept
-----------------------------------------------------------

Obsolete markers
---------------------------------

The mutable concept is based on **obsolete markers**. Creating an obsolete
marker registers a relation between an old obsoleted changeset and its newer
version.

Old changesets are called **precursors** while their new versions are called
**successors**. A marker always registers a single *precursor* and:

- no *successor*: the *precursor* is just discarded.
- one *successor*: the *precursor* has been rewritten
- multiple *successors*: the *precursor* were splits in multiple
  changesets.

.. The *precursors* and *successors* terms can be used on changeset directy:

.. :precursors: of a changeset `A` are changesets used as *precursors* by
..              obsolete marker using changeset `A` as *successors*

.. :successors: of a changeset `B` are changesets used as *successors* by
..              obsolete marker using changeset `B` as *precursors*

Chaining obsolete markers is allowed to rewrite a changeset that is already a
*successor*. This is a kind of *second order version control*.
To clarify ambiguous situations one can use **direct precursors** or
**direct successors** to name changesets that are directly related.

The set of all *obsolete markers* forms a direct acyclic graph the same way
standard *parents*/*children* relation does. In this graph we have:

:any precursors: are transitive precursors of a changeset: *direct precursors*
                 and *precursors* of *precursors*.

:any successors: are transitive successors of a changeset: *direct successors*
                 and *successors*  of *successors*)

Obsolete markers may refer changesets that are not known locally.
So, *direct precursors* of a changeset may be unknown locally.
This is why we usually focus on the **first known precursors**  of the rewritten
changeset. The same apply for *successors*.

Changeset in *any successors* which are not **obsolete** are called
**newest successors**..

.. note:: I'm not very happy with this naming scheme and I'm looking for a
          better distinction between *direct successors* and **any successors**.

Possible changesets "type"
---------------------------------

The following table describes names and behaviors of changesets affected by
obsolete markers. The left column describes generic categories and the right
columns are about sub-categories.


+---------------------+--------------------------+-----------------------------+
| **mutable**         | **obsolete**             | **extinct**                 |
|                     |                          |                             |
| Changeset in either | Obsolete changeset is    | *extinct* changeset is      |
| *draft* or *secret* | *mutable* used as a      | *obsolete* which has only   |
| phase.              | *precursor*.             | *obsolete* descendants.     |
|                     |                          |                             |
|                     | A changeset is used as   | They can safely be:         |
|                     | a *precursor* when at    |                             |
|                     | least one obsolete       | - hidden in the UI,         |
|                     | marker refers to it      | - silently excluded from    |
|                     | as precursors.           |   pull and push operations  |
|                     |                          | - mostly ignored            |
|                     |                          | - garbage collected         |
|                     |                          |                             |
|                     |                          +-----------------------------+
|                     |                          |                             |
|                     |                          | **suspended**               |
|                     |                          |                             |
|                     |                          | *suspended* changeset is    |
|                     |                          | *obsolete* with at least    |
|                     |                          | one non-obsolete descendant |
|                     |                          |                             |
|                     |                          | Thoses descendants prevent  |
|                     |                          | properties of extincts      |
|                     |                          | changesets to apply. But    |
|                     |                          | they will refuse to be      |
|                     |                          | pushed without --force.     |
|                     |                          |                             |
|                     +--------------------------+-----------------------------+
|                     |                          |                             |
|                     | **troubled**             | **unstable**                |
|                     |                          |                             |
|                     | *troubled*    has        | *unstable* is a changeset   |
|                     | unresolved issue caused  | with obsolete ancestors.    |
|                     | by *obsolete* relations. |                             |
|                     |                          |                             |
|                     | Possible issues are      | It must be rebased on a     |
|                     | listed in the next       | non *troubled*    base to   |
|                     | column. It is possible   | solve the problem.          |
|                     | for *troubled*           |                             |
|                     | changeset to combine     | (possible alternative name: |
|                     | multiple issue at once.  | precarious)                 |
|                     | (a.k.a. divergent   and  |                             |
|                     | unstable)                +-----------------------------+
|                     |                          |                             |
|                     | (possible alternative    | **bumped**                  |
|                     | names: unsettled,        |                             |
|                     | troublesome              | *bumped* is a changeset     |
|                     |                          | that tries to be successor  |
|                     |                          | of  public changesets.      |
|                     |                          |                             |
|                     |                          | Public changeset can't      |
|                     |                          | be deleted and replace      |
|                     |                          | *bumped*                    |
|                     |                          | need to be converted into   |
|                     |                          | an overlay to this public   |
|                     |                          | changeset.                  |
|                     |                          |                             |
|                     |                          | (possible alternative names:|
|                     |                          | mislead, naive, unaware,    |
|                     |                          | mindless, disenchanting)    |
|                     |                          |                             |
|                     |                          +-----------------------------+
|                     |                          | **divergent**               |
|                     |                          |                             |
|                     |                          | *divergent*   is changeset  |
|                     |                          | that appears when multiple  |
|                     |                          | changesets are successors   |
|                     |                          | of the same precursor.      |
|                     |                          |                             |
|                     |                          | *divergent*   are solved    |
|                     |                          | through a three ways merge  |
|                     |                          | between the two             |
|                     |                          | *divergent*   ,             |
|                     |                          | using the last "obsolete-   |
|                     |                          | -common-ancestor" as the    |
|                     |                          | base.                       |
|                     |                          |                             |
|                     |                          | (*splitting* is             |
|                     |                          | properly not detected as a  |
|                     |                          | conflict)                   |
|                     |                          |                             |
|                     |                          | (possible alternative names:|
|                     |                          | clashing, rival, concurent, |
|                     |                          | conflicting)                |
|                     |                          |                             |
|                     +--------------------------+-----------------------------+
|                     |                                                        |
|                     | Mutable changesets which are neither *obsolete* or     |
|                     | *troubled*    are *"ok"*.                              |
|                     |                                                        |
|                     | Do we really need a name for it ? *"ok"* is a pretty   |
|                     | crappy name :-/ other possibilities are:               |
|                     |                                                        |
|                     | - stable (confusing with stable branch)                |
|                     | - sane                                                 |
|                     | - healthy                                              |
|                     |                                                        |
+---------------------+--------------------------------------------------------+
|                                                                              |
|     **immutable**                                                            |
|                                                                              |
| Changesets in the *public* phases.                                           |
|                                                                              |
| Rewriting operation refuse to work on immutable changeset.                   |
|                                                                              |
| Obsolete markers that refer an immutable changeset as precursors have        |
| no effect on the precussors but may have effect on the successors.           |
|                                                                              |
| When a *mutable* changeset becomes *immutable* (changing its phase from draft|
| to public) it is just *immutable* and loose any property of it's former      |
| state.                                                                       |
|                                                                              |
| The phase properties says that public changesets stay as *immutable* forever.|
|                                                                              |
+------------------------------------------------------------------------------+



Command and operation name
---------------------------------


Existing terms
``````````````

Mercurial core already uses the following terms:

:amend: to rewrite a changeset
:graft: to copy a changeset
:rebase: to move a changeset


Uncommit
`````````````

Remove files from a commit (and leave them as dirty in the working directory)

The *evolve* extension have an `uncommit` command that aims to replace most
`rollback` usage.

Fold
``````````

Collapse multiple changesets into a unique one.

The *evolve* extension will have a `fold` command.

Prune
``````````

Make a changeset obsolete without successors.

This an important operation as it should mostly replace *strip*.

Alternative names:

- kill: shall has funny effects when you forget "hg" in front of ``hg kill``.
- obsolete: too vague, too long and too generic.

evolve
```````````````

Automatically resolve *troublesome* changesets
(*unstable*, *bumped* and *divergent*)

This is an important name as hg pull/push will suggest it the same way it
suggest merging when you add heads.

alternative names:

- solve (too generic ?)
- stabilize