Evolve User Interface Discussion


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There are a number of things that have to be discussed about how the Evolve UI works.

1. Low Hanging Fruits

Check the list easy bug and feature request related to evolution

Here is an handfull of highlight (but you should just check the bts list)

If you feel bold also look at all evolution related bug on the BTS

2. Glossary

Which language should we use for Evolve? Remember that once this goes into core, this language gets frozen forever.

2.1. Command names

/!\ This sub-section need rework/splitting/movement/unicorn before being useful

2.2. Concepts

/!\ This section need rework/splitting/movement/unicorn before being useful

2.3. Terminology Opinions

/!\ This section need rework/splitting/movement/unicorn before being useful

Ideally we're searching for a grammar where everything is related. If we have words that are closely associated in the English language, users will associate them with related version control tasks. It reduces the potential for confusion and increases the probability for knowledge recall. With that in mind, I'm not sure words like "evolve" and "troubled" go together well. You wouldn't think "this thing is troubled, therefore I'm going to evolve it." I would think "stablize" or "solve" would be much better verbs to complement "troubled." "This thing is troubled, therefore I'm going to stablize it" makes more sense, IMO. But I think there's still room for improvement in the grammar. --indygreg

An idea is to name unstable changesets dangling changesets, to name bumped changesets dangling replacements, and to name divergent changesets conflicting replacements. Here, "dangling" means "doesn't have a suitable parent". In the case of normal changesets, this means that the parent is obsolete. In the case of replacement changesets, this means that the parent is public. -- tomjb

3. Commands

/!\ This section wants to be:

4. hg fold

4.1. Current state

The current behavior can be illustrated easily with the following examples:

4.2. Why?

In the dawn of time, the behavior was: hg fold <revset>:

There was two issue with this UI:

  1. It pretty much requires the knowledge of revset to be used efficiently. This put the barrier of entry higher than necessary for a fairly basic command.
  2. The most common case turned out to be, I want to fold the last N commits. This happen commonly when one is working toward something, making frequent wip commit along the way to be able to easily go back to a check point. So the common case was hg fold X::.

So, we move the default to :

This also makes sense because most of mercurial command behave according the working directory parent

4.3. Open Questions

5. Behavior

6. Automatic "hg evolve" call

/!\ This sub section need rework/splitting/movement/unicorn before being useful

/!\ no decision are will be made on this any time soon, concider using your brain power elsewhere.

Many evolve commands produce unstable changesets. Should they immediately call hg evolve by default?

6.1. pros

6.2. cons

Perhaps ui.autoevolve option? On by default? Off by default?

I think auto evolve makes sense in some cases. For example, say you amend a commit with descendants and only change the commit message. Why wouldn't you want auto evolve in that scenario? -- indygreg

I'd be OK with having an autoevolve option (on first blush I'd rather have it be enabled by default, but I'd need to use evolve more to be sure. Maybe that would lead to having too many obsolete revisions). -- AngelEzquerra

What about an intermediate behavior? Couldn't it be possible to do a sort of "dry run evolve" which detected if there would be any conflicts during evolve, and if there weren't (e.g. in cases in which we just edited the changeset metadata). I think this would achieve 80% of the magic with 0% of the risk -- AngelEzquerra

I think the "there are now troubled commits message" should be actionable. Currently it just prints the count of troubled commits. I'd really like to see a "run hg evolve to stablize" message. If we don't auto evolve, at least we can tell the user what they should probably be doing next. -- indygreg

7. Use Cases

7.1. Undoing an amend

Users will often accidentally amend a commit. We need a good story to undo them.

This mean changing the commit content, but not touching the working directory. The hg uncommit command is already responsible for this action.

Growing a was to easily call uncommit on the precursor instead of the parent would fit that need:

(Git have a git reset HEAD@{1} notation for this. However, introducing a git-reset like command in Mercurial is a non-goal)

8. Pain Points

8.1. Evolve can "stabilise" to unstable destination

8.1.1. Situation

Start with a linear graph:

and amend 1 and 3 to create aa' and bb'. This gives us this graph:

The red changesets are marked as obsolete, and the orange changesets are thus troubled. Starting from bb, getting this repo back into an untroubled state takes 6 calls to 'hg evolve', the last 4 of which need --any.

8.1.2. Explanation of the current behavior

This happens because evolve first started to rebase c and cc on B. After that it asked to --any to start evolving B, BB' and C' and CC' over aa'.

8.1.3. Possible improvement

The shortest path to stabilization would have been to take care of B and BB' first then directly evolve C and C on the result.

The fact that hg evolve think evolve B is unrelated to BB' (then requires --any) sounds wrong too.

Both point can be fixed if we make evolving ancestors "relevant to the context" (not requires any).

(This case is not a valid case in favor of hg evolve --all)

8.2. The obsolete history is not very usable

/!\ This section need some clarification /!\ consider using a 1. Example 2. explanation 3. possible actions format

In order for evolve to achieve its full potential the hidden history that that evolve creates must be not only useful for enabling amending shared revisions but also _usable_ by the user to get back to old versions of a given revision (e.g. in case that the user is not happy with a later version of that revision).

Currently the obsolete history created by evolve is not very usable because the number of hidden, obsolete revisions created by evolve is greater than it should. In particular:

- Each history modification step creates its own set of obsolete revisions. There is no way to perform several history editing operations and combining those into a single operation.

/!\ Why do you say evolve creates more obsolete changeset that it could. Do you have a concrete example of situation where it does? (beside the extra temporary commit thing)

-- AngelEzquerra When I use MQ I often import a bunch of revisions into MQ, I unapply some (maybe a lot) of them, I reorder them, reapply them, fold some, split some, amend some... With evolve, each and every one of those actions will potentially create as many obsolete revisions as the number of revisions I would have imported into MQ. With some planning, perhaps using the reorder command or thinking ahead I could minimize the number or revisions, but still, for any non trivial history editing operation (and perhaps even for some trivial operations) the number of obsolete revisions may explode. Even worse, when using a GUI it may be even harder to "plan" to reduce the number of obsolete revisions as each GUI operation must be mapped to evolve commands.

Another thing that comes to mind and that I think contributes to this feeling that evolve creates too many revisions is that obsolete revisions don't have record of the evolve operation that created them. What I mean by that is that you may do 3 history editing operations and get a lot more obsolete revisions. But I don't really care about those revisions individually. Instead I care about the 4 states of the repo related to those 3 history editing operations (original state, state after operation 1, state after operation 2, state after operation 3). Which leads me to the filtering idea below.

An alternative to this would be for evolve to provide tools to filter or show the obsolete history somehow.

/!\ This second point is very interesting, there is multiple direction where we could improve that. Can you elaborate on your filtering idea?

-- AngelEzquerra: What I'm thinking is that there should be a way to to show repository "states", instead of showing all the obsolete revisions.

I think that once I'm done editing my story I a generally only care about the original state (right before I editing history) and the state afterwards (the one that is visible, i.e. not obsolete). _While_ I am editing history I will probably also care with the state right before the last evolve operation, and much less often about the other intermediate states (as in states after an evolve operation). Usually I would only care about intermediate states if I made a mistake or I wanted to go back to a previous state).

We we could do a couple of things: 1. Track the actions that created sets of obsolete operations (i.e. repo states) 2. We could perhaps track when we start editing history (e.g. when we do our first history editing operation after a non history editing operation) and when we finish (e.g. when we do the first non history editing operation after a non history editing operation after a group of editing operations). In doing so we could automatically tell which was the "original state" and make it accessible through some revset, or have some log option that would only show those _evolve start_ states. If we also tracked the evolve operations that created the obsolete revisions we could filter the log by the different states the repo went through during the history editing operations, effectively letting you turn back the clock to any previous state in your repo.

I don't know if this makes sense to you guys...

9. F.A.Q.

9.1. Why do we have a temporary commit after amend?

It is an implementation details that will eventually be removed

9.2. Why are hidden changesets not pushed to remote?

Pushing all hidden changeset to the remote by default does not seems to be an interesting goal. However having some way to push or pull some obsolete/hidden changeset in some case seems useful and will probably happen. (This is however not very high priority right now).

CategoryDeveloper CategoryEvolution

CEDUserInterface (last edited 2017-01-23 13:47:00 by Pierre-YvesDavid)