Document number: P2138R3
Audience: EWG, LEWG

Ville Voutilainen

Rules of Design<=>Specification engagement


First things first: this paper is a process description, and the main audience is Working Group and Study Group chairs, their assistants, and WG21 expert members who do proposal reviews. This paper is not a tutorial for writing good proposals - although keen-eyed readers may find the description useful for producing high-quality proposals.

This paper explains the rules of engagement that have been in use between Evolution and Core, amends the rules with regards to Evolutionary specification review, and proposes adopting the same rules between Library Evolution and Library.

The amendment to the rules should change nothing for Core and Library (well, not for worse, at least), it's merely a specification-runthrough in EWG and LEWG before the material proceeds for technical/specification review. But as a formal addition, there is a step after the specification review to review available implementation/deployment experience; this review is to be done by both the Design and the Specification group. Whether the groups want to combine forces for that review or perform it separately is left up to their discretion, but both groups should perform that review, because they will be doing so from different viewpoints with a different emphasis.

The proposal ALSO proposes a new Tentatively Ready state between specification review and plenary poll. This is proposed in order to give reviewers time to digest new proposals. Said state can be bypassed in urgent situations, but by default, it's proposed in order to allow for gathering more implementation/deployment experience, experiment feedback, and other feedback.

To repeat and rephrase, this proposal attempts to improve the following abilities:

The <=> in the title is not a spaceship, it's two overlapping arrows going into opposite directions.

Revision history

Highlight the most recent changes:

Highlight the R1->R2 changes:

Highlight the R0->R1 changes:

Further elaboration on the problems this proposal aims to tackle

Here's an alternative way to put it, in three parts:

  1. Avoid wasting time in the various stage of the pipeline. Especially avoid wasting time in the stages that are our bottlenecks, aka the specification review.
  2. Define what it requires to advance from one pipeline stage to the next.
  3. Define checkpoints for going back from one pipeline stage to an earlier one, if necessary.

Here's why we propose to introduce new checkpoints for possibly going back to earlier pipeline stages, and the problem we're trying to tackle by doing so, as phrased by Peter Dimov:

    Roughly and approximately, the problem that the committee can potentially
    inflict billions of dollars of damage on the C++ community by breaking code
    in a sufficiently problematic way. This requires a certain amount of due

Some remarks of the alleged downsides of this proposal

The following concerns might be raised about this proposal:

  1. it introduces very stringent gatekeeping
  2. it makes the process harder for new committee members

For the first, it should be pointed out that this proposal doesn't actually introduce anything new; we have done all of the things in it in an inconsistent fashion, sometimes doing it, sometimes not. This proposal changes what our defaults are, and allows bypassing those defaults if we make an Educated Decision to do so.

For the second, this proposal makes our pipeline stages officially-specified for everybody, both old and new committee members. And it gives new and old committee members a process specification that they can read, as opposed to relying on hearsay and never really knowing what to expect.

Finally, while stringent gatekeeping might seem like a nuisance to some, and a multi-stage process that requires multiple championing steps might be inconvenient for proposal authors who can't attend multiple meetings, all that must be secondary to the ultimate goal of all of this, which is a higher-quality International Standard. This is simply not negotiable.

Some historical background

The original problem

Way back when, not really important when, but a couple of years ago, we had three problematic issues with material that flowed from Evolution to Core:

The solution

To alleviate these problems, the Chair of Evolution specified the following rules, although they weren't written down (a snag that this document aims to rectify):

The rationale for these points shouldn't be hard to understand:

The process

Once these issues were recognized and the alleviation for them agreed on, we established the following process for Design->Specification:

And, as mentioned earlier, the following process for Design<-Specification:

The New Rules

These rules apply to both EWG->CWG and LEWG->LWG. Furthermore, there is now a new Tentatively Ready step between specification review and a plenary poll.

Rather than the chair of a design group making sure that wording exists and is ready for the technical/specification review group's consumption, that responsibility now lies with the whole design group. That is, once the proposal author has made sure their wording is either written by a wordsmith or reviewed by one, they approach the design group (with the wordsmith) and give a presentation about the wording, illustrating how it implements the design, and report whether any oddities or questions surfaced. If such oddities or questions did surface, the design group needs to discuss them and possibly clarify their design.

This rule change is made for a couple of reasons:

"What's a 'wordsmith'? Who qualifies?"

A wordsmith is, by the definition for the purposes of this process, "a person who can write or help write CWG/LWG-consumable wording". It's ultimately the decision of the chairs of EWG/LEWG to decide what sort of wording they're willing to accept as wording incoming into their specification review (which might be less strict than the specification-group review), and those groups should have confidence that what they forward is written and championed by a person that won't be wasting Core's or Library's time.

CWG and LWG can also, if they so choose, arrange for a small group of their members to do this specification-work. Note, however, that such arranging must not consume group time, and is not the responsibility of the chair of the specification review group.

The solicitation for wording assistance is highly recommended to have roughly the following priority order:

  1. The members of EWG/LEWG should be queried for volunteers to help with wording when the initial design review is done.
  2. Well-known wordsmiths can be asked for help by more seasoned EWG/LEWG members, which is a slight variation of the above.
  3. Wording assistance requests can be made on the reflector.

It is not appropriate to spend CWG's or LWG's time in the quest for a wordsmith, as a group.

Further explanation of the new process

So, to sum it up, let's bulletize the Design->Specification process:

  1. The design group, be it LEWG or EWG, decides after reviewing a proposal that it should go forward to LWG or CWG.
  2. In all the subsequent steps, both the wordsmith and the proposal author/champion should be available and present. That includes both the Design group's wording review and the Specification group's wording review.
  3. If the proposal has wording, the design group must run through it and verify that the design is wholly and accurately implemented by the wording, and that there are neither omissions nor additions that the design doesn't cover.
  4. If the proposal does not have wording, the design group must not greenlight the proposal to go forward; they must instead instruct the proposal to come back with the wording.
  5. When the proposal has new wording not yet reviewed in the second bullet, go back to the third bullet. Repeat as many times as necessary.
  6. Once the run-through is complete, and the design group is confident that the wording implements the design wholly and accurately, the design group sends the material onwards, forwards.

Let's also bulletize the Design<-Specification process, and also the steps between Specification->Plenary:

  1. The specification/technical review group reviews a proposal and discovers a design-level addition/omission/bug/issue/snag, or a technical problem (an implementability problem, a consistency problem, or some other problem).
  2. The chair of the specification/technical review group makes sure the problem is minuted, sends a heads-up to the chair of the design group, and designates a champion that can explain the problem to the design group.
  3. The design group reviews the matter, and resolves it according to the Design->Specification process.
  4. The specification/technical review group continues progress on the proposal.
  5. Once the specification review is complete, both the Specification group and the Design group look at the available implementation/deployment experience of the proposal.
  6. If that experience is deemed sufficient, the proposal is made Tentatively Ready for a plenary poll.
  7. If there's feedback that necessitates looking again at either the design or the specification, the proposal is sent back to those stages.
  8. Otherwise, proceed to the plenary poll *in the next meeting*.
  9. Bypassing the Tentatively Ready status after design review or the Tentatively Ready for Plenary status after specification review is allowed by the process, but

Or in a diagram: