Publish only a commit on its module's trunk; post a pull request's change plan (hq ADR 0238)

One commit, one plan: a commit off the trunk — a pull request's head, a branch built by
hand, a rebuild or replay of one — is for checking. The build seat reads from its clone
which branches hold the commit, and the controller records and never registers a build
whose commit is not on the branch the module follows (the repository's default for a
new one), so nothing off the trunk can be sent.

A pull request's check now carries its change plan, computed by the planner: what a
merge would build in which order, what each machine would receive, and what is not an
ordinary send — the bus step, a module waiting for a person, a provider's consumers.

cmd/mesh-controller/checks.go

@@ -74,6 +74,8 @@ type checkScope struct {
 	Judge string
 	// From is a module built from the repository, for how the mesh clones it; nil when none is.
 	From *inventory.Entry
+	// Reach is the planner's whole answer, which the change plan is made from.
+	Reach mergeReach
 }
 
 func (s checkScope) gated() bool { return len(s.Modules)+len(s.New) > 0 }
@@ -88,7 +90,7 @@ func pullScope(p link.PullUpdated, entries []inventory.Entry, read map[string][]
 		ModuleDirsSaid: p.ModuleDirsSaid}
 	r := reachOfMerge(m, entries, read, edges)
 	s := checkScope{Modules: r.Moved(), Dependents: r.Dependents(), New: r.Added, Unread: r.Unread,
-		Width: len(r.Plan.Modules), Tiers: len(r.Plan.Tiers)}
+		Width: len(r.Plan.Modules), Tiers: len(r.Plan.Tiers), Reach: r}
 	for _, e := range append(append([]inventory.Entry{}, r.Touched...), r.Deleted...) {
 		s.Manifests = append(s.Manifests, path.Join(strings.Trim(e.Source.Path, "/"), moduleManifestFile))
 		switch e.Manifest.Module {
@@ -150,9 +152,16 @@ func (f following) PullUpdated(ctx context.Context, p link.PullUpdated) error {
 		return err
 	}
 	scope := pullScope(p, entries, read, edges)
+	// The change plan of the commit at hand (ADR 0238): what a merge of it would build and send, posted
+	// with the verdict whatever the verdict is.
+	plan := changePlanOf(p.Owner+"/"+p.Repo, p.Base, p.Commit, scope.Reach, entries, func(module string) (inventory.Upgrade, bool) {
+		u, err := inv.UpgradeOf(ctx, module)
+		return u, err == nil
+	})
+	fmt.Print(planText(plan))
 	direct := link.Checked{Owner: p.Owner, Repo: p.Repo, Number: p.Number, Commit: p.Commit,
 		ID: link.NewBuildID(time.Now()), Verdict: "pass", Summary: noModuleTouched,
-		Gate: &link.CheckLayer{Verdict: "pass", Summary: noModuleTouched}}
+		Gate: &link.CheckLayer{Verdict: "pass", Summary: noModuleTouched}, Plan: &plan}
 	switch {
 	case !scope.gated() && !scope.Mesh:
 		fmt.Printf("%s/%s#%d (%.8s): %s, and the repository is not the mesh's: said, nothing run\n",
@@ -169,6 +178,7 @@ func (f following) PullUpdated(ctx context.Context, p link.PullUpdated) error {
 	if err != nil {
 		return err
 	}
+	request.Check.Plan = &plan
 	seat := buildSeatHeld(ctx)
 	ask, err := askOverOn(seat)
 	if err != nil {
@@ -326,6 +336,9 @@ func checkedOf(result link.BuildResult) link.Checked {
 	if result.Checked != nil && c.Gate != nil && len(c.Gate.Dependents) == 0 {
 		c.Gate.Dependents = result.Checked.Dependents
 	}
+	if result.Checked != nil {
+		c.Plan = result.Checked.Plan
+	}
 	for _, l := range []*link.CheckLayer{c.Gate, c.RepoCheck} {
 		if l != nil && l.Verdict == "" {
 			l.Verdict = "error"