Changeset Evolution - Vocabulary

This page is intended for developers

This page gathers data from discussion about the name use within the ChangesetEvolution concept.

2017 March 15 Meeting

Conclusions

Introduction to Instability

Rewriting changesets may introduce instability.

There are two main kinds of unstable changesets: orphaned changesets and divergent changesets.

Orphans are changesets left behind when their ancestors are rewritten.

Divergence has two variants:

• Content-divergence occurs when independent rewrites of the same changeset lead to different results.

• Phase-divergence occurs when the old (obsolete) version of a changeset becomes public.

Renames

• Troubles => Instability

• Troubled => Unstable

• Precursor => Predecessor

• Unstable => Orphan

• Divergent => Content-divergent

• Bumped => Phase-Divergent

• evolve => stabilize

• Evolution => Stabilization

Notes

Overview:

• We have already agreed on the developer-facing things:
  • Obsolete is a good term for developers
  • Precursor is being renamed predecessor
  • Successor will remain successor
• There is some agreement about changing the name "troubles" to "instability" and having having the main command be "stabilize" rather than "evolve"
• We are trying to come up with names for the user-facing. They are currently called:
  • Troubles
  • Unstable
  • Divergent
  • Bumped

More discussion:

• One idea: UI sentences can include "simpler" phases such as "left behind". For example: "3 changesets were left behind and are now orphans".

Naming ideas:

• Unstable:
  • Orphan
  • Obsbased
  • Dangling
  • Left Behind
• Divergent:
  • Competing
  • Alternates
• Bumped:
  • Divergent

Important points:

• ability to Google the terms

Sentences describing things:

• Rewriting changesets you shared with other repository might introduce instability.

Two terms:

• There are two main kinds of instability: orphaning and diverging.
• There are two main kinds of instability: orphaning and diverging (content and phase).
• There are two main kinds of unstable changesets: orphaned and diverged.
• There are two main kinds of unstable changesets: orphaned and diverged (content and phase).

Three terms:

• There are three kinds of instability: orphaning, content-variance, and phase-divergence.

Unstable:

• "Orphans" are changesets left behind when their ancestors are rewritten

Divergence:

• "Content-diverged" changesets occur when independent rewrites of the same changesets lead to different results.
• "Changes-diverged" changesets occur when independent rewrites of the same changesets lead to different results.
• "Content-variants" are changesets created by independent rewrites of the same changeset(s).

Bumped:

• "Phase-diverged" changesets occur when their old (obsolete) versions are made public.
• "Divergent" changesets occur when their old (obsolete) versions are made public.
• "Phase-variants" are changesets that occur when their old (obsolete) versions are made public.

Older Discussions

Troubles

"troubled" changeset and troubles

Evolving history can introduce problems that need to be solved:

• They are intrinsic side effects of the free exchange and rewrite of draft changesets,
• They are an unhealthy state the user needs to take care of before moving forward,
  • (Even if they can stay around unsolved for a while),
• They are not critical, we know how to detect and solve them,
• There are different kinds of them.

"unstable" changeset and "instability"

Related documentation

Instability happens when a changeset with descendants is rewritten. The non-obsolete descendants of the now obsolete changeset are called "unstable changesets".

A Changeset is "unstable" because either:

• one of its parents is obsolete,
• one of its parents is unstable.

Automatic resolution of instability by rebasing the unstable changesets on the latest known successors of their obsolete parent. (A changeset that is unstable because its parent is unstable needs to wait for the unstable parent to be stabilized before we can solve it.)

"Bumped" changeset and "bumping"

related documentation

A changeset is called "Bumped" when it is the successor of a public changeset. The public changeset cannot be obsoleted or hidden anymore so both the old and new versions exist. This usually happens when someone is reworking a changeset while someone else is publishing it at the same time elsewhere. The two actions are eventually gathered somewhere and evolve detects there is an issue. To some extend "bumping" can be seen as "divergence with your past" as opposed to "divergence with another rewriting that happened in parallel).

So in summary bumped changesets are:

* superseding something public, * trying to obsolete something that cannot be obsolete, * trying to bring "a change" but they are too late to do so.

The automated solution for this is to create a new changeset with the diff between the public changeset and the successors (The diff introduced by the amend).

"divergent" changeset and "divergence"

Divergence happens when two changesets claim to have superseded the same changeset. The canonical way to do this is to have two people in two different repos rewriting the same changeset. The divergence is detected when one pulls from the other. (There is currently no other easy way to get divergence locally).

* Divergence denotes that two (or more) different and independent "edits" happened on the same changeset, * No version can be called "better/newer" than the other one, so both are "alive" at the same time, duplicating all the common changes, * There is at least one latest common precursor that both divergent changesets claim to rewrite. They are said to be divergent from that latest common precursor. * A divergent changeset is divergent with the other non-obsolete changeset.

The automated way to solve this, is to merge the two divergent changesets using the precursor they are divergent from as a base.

Obsolescence graph

Obsolescence markers create an orthogonal graph between the changesets, that track what changeset gets rewritten into which other. For this we use obsolescence-marker. A small data structure that contains various information including the fact that "Changesets [Y] are replacing changeset X". We are interested in names used to describe the X ← Y relation. In both directions and from the point of view of each side of it.

"Successor"

"successor" are the "new" part of that relation.

"Precursor"

"precusor" are the "old" part of that relation. The precursors will become obsolete and hidden (except in multiple cases).

See Also

• mailing list discussion about evolution naming

• CEDUserInterface#Terminology_Opinions

• mailing list discussion: [RFC] naming of obsolescence troubles (2012-September)

• mailing list discussion: Obsolete Terminology (2012-July)

  • continued (2012-August)

• etherpad with notes: https://public.etherpad-mozilla.org/p/evolve-naming_NO_SPAM

CategoryDeveloper CategoryEvolution