Build for the merge from a copy its tests never touch, and keep or take only the same head's build

The gate and the repository's check mount the workspace read-write, so a
build from that tree could hold what the tests wrote under a key that
describes the merge. A check now clones the merge outside the workspace
before anything of the change runs, and builds from that. A check keeps,
and a walk takes, only a build an earlier check of the same pull request
at the same head made: another pull request's build, or an earlier
head's, is never registered. The walk reads the verdicts once
(novox/hq issue 703, review of #328).

cmd/mesh-controller/batches.go

@@ -688,7 +688,7 @@ func spelledOf(m inventory.BatchedMerge) string {
 func namedOf(m inventory.BatchedMerge, repository string) inventory.PlanMerge {
 	k := announcedOf(m)
 	return inventory.PlanMerge{Repository: repository, Commit: m.Commit, Number: k.Number, Title: k.Title, Moves: k.Moves,
-		Merged: m.Merged, Heard: m.Heard}
+		Head: k.HeadSHA, Merged: m.Merged, Heard: m.Heard}
 }
 
 // laterMerge says a was merged after b: by the forge's merge time, then by when each was heard.

cmd/mesh-controller/check_builds_test.go

@@ -190,52 +190,75 @@ func TestAReusedCheckBuildIsRegisteredByItsDigestAndGatedAsABuiltOne(t *testing.
 	}
 }
 
-// A walk's leave names the builds its own pull requests' verdicts made, and none when they cannot be read: the
-// builder takes nothing a verdict does not name (novox/hq ADR 0350 §2).
+// A walk's leave names the builds its own pull requests' verdicts made at the head each merge merged — never an
+// earlier head's — read once per walk, and none when they cannot be read: the builder takes nothing a verdict does
+// not name (novox/hq ADR 0350 §2, issue 703).
 func TestAWalksLeaveNamesTheBuildsItsPullRequestsVerdictsMade(t *testing.T) {
 	was := checkedBuildsOf
-	t.Cleanup(func() { checkedBuildsOf = was })
-	var asked []link.PullRef
-	named := []link.CheckedBuild{{Pull: link.PullRef{Owner: "novox", Repo: "shop", Number: 7}, Check: "build-1",
-		Built: link.CheckBuilt{Module: "app", Key: "r1:1"}}}
+	forgetWalkVerdicts()
+	t.Cleanup(func() { checkedBuildsOf = was; forgetWalkVerdicts() })
+	var asked [][]link.PullRef
+	pull := link.PullRef{Owner: "novox", Repo: "shop", Number: 7}
+	atHead := link.CheckedBuild{Pull: pull, Check: "build-2", Head: "bbbbbbbbbbbb", Built: link.CheckBuilt{Module: "app", Key: "r1:2"}}
+	earlier := link.CheckedBuild{Pull: pull, Check: "build-1", Head: "aaaaaaaaaaaa", Built: link.CheckBuilt{Module: "app", Key: "r1:1"}}
 	checkedBuildsOf = func(_ context.Context, pulls []link.PullRef) ([]link.CheckedBuild, error) {
-		asked = pulls
-		return named, nil
+		asked = append(asked, pulls)
+		return []link.CheckedBuild{atHead, earlier}, nil
 	}
-	pulls := []link.PullRef{{Owner: "novox", Repo: "shop", Number: 7}}
-	if got := reuseWithVerdicts(t.Context(), &link.ReuseAsk{Pulls: pulls}); !reflect.DeepEqual(got.Builds, named) ||
-		!reflect.DeepEqual(asked, pulls) {
-		t.Fatalf("the leave names %+v, read for %+v", got.Builds, asked)
+	pulls := []link.PullRef{pull}
+	heads := map[link.PullRef]string{pull: "bbbbbbbbbbbb0123456789"}
+	for range 3 {
+		if got := reuseWithVerdicts(t.Context(), "plan-1", &link.ReuseAsk{Pulls: pulls}, heads); !reflect.DeepEqual(got.Builds,
+			[]link.CheckedBuild{atHead}) {
+			t.Fatalf("the leave names %+v, not only the merged head's build", got.Builds)
+		}
+	}
+	if !reflect.DeepEqual(asked, [][]link.PullRef{pulls}) {
+		t.Fatalf("the verdicts were read %d times for one walk: %v", len(asked), asked)
+	}
+	// A merge whose head was not said takes nothing.
+	if got := reuseWithVerdicts(t.Context(), "plan-1", &link.ReuseAsk{Pulls: pulls}, nil); got.Builds != nil {
+		t.Fatalf("a merge of no said head names %+v", got.Builds)
 	}
 	checkedBuildsOf = func(context.Context, []link.PullRef) ([]link.CheckedBuild, error) {
 		return nil, errors.New("no bus")
 	}
-	if got := reuseWithVerdicts(t.Context(), &link.ReuseAsk{Pulls: pulls}); got.Builds != nil {
+	if got := reuseWithVerdicts(t.Context(), "plan-2", &link.ReuseAsk{Pulls: pulls}, heads); got.Builds != nil {
 		t.Fatalf("verdicts that could not be read named %+v", got.Builds)
 	}
 }
 
-// A check is handed the builds the seat's verdicts name for the modules it builds, read once, and none when they
-// cannot be read (novox/hq issue 703).
-func TestACheckIsHandedTheBuildsTheVerdictsNameForItsModules(t *testing.T) {
-	was := checkedBuildsOfModules
-	t.Cleanup(func() { checkedBuildsOfModules = was })
-	var asked [][]string
-	named := []link.CheckedBuild{{Pull: link.PullRef{Owner: "novox", Repo: "shop", Number: 7}, Check: "build-1",
-		Built: link.CheckBuilt{Module: "app", Key: "r1:1"}}}
-	checkedBuildsOfModules = func(_ context.Context, modules []string) ([]link.CheckedBuild, error) {
-		asked = append(asked, modules)
-		return named, nil
+// A check is handed only the builds earlier checks of its own pull request at its own head made: another pull
+// request's build, or an earlier head's, is never kept (novox/hq issue 703). None when they cannot be read.
+func TestACheckIsHandedOnlyItsOwnHeadsBuilds(t *testing.T) {
+	was := checkedBuildsOf
+	t.Cleanup(func() { checkedBuildsOf = was })
+	pull := link.PullRef{Owner: "novox", Repo: "shop", Number: 7}
+	mine := link.CheckedBuild{Pull: pull, Check: "build-1", Head: "bbbbbbbbbbbb", Built: link.CheckBuilt{Module: "app", Key: "r1:1"}}
+	earlier := link.CheckedBuild{Pull: pull, Check: "build-0", Head: "aaaaaaaaaaaa", Built: link.CheckBuilt{Module: "app", Key: "r1:1"}}
+	another := link.CheckedBuild{Pull: link.PullRef{Owner: "novox", Repo: "shop", Number: 8}, Check: "build-9",
+		Head: "bbbbbbbbbbbb", Built: link.CheckBuilt{Module: "app", Key: "r1:1"}}
+	var asked [][]link.PullRef
+	checkedBuildsOf = func(_ context.Context, pulls []link.PullRef) ([]link.CheckedBuild, error) {
+		asked = append(asked, pulls)
+		return []link.CheckedBuild{mine, earlier, another}, nil
 	}
-	builds := []link.CheckBuild{{Module: "app"}, {Module: "web", Skip: "the merge deletes it"}}
-	if got := namedForTheCheck(t.Context(), builds); !reflect.DeepEqual(got, named) ||
-		!reflect.DeepEqual(asked, [][]string{{"app"}}) {
-		t.Fatalf("the check is handed %+v, read %v", got, asked)
+	p := link.PullUpdated{Owner: "novox", Repo: "shop", Number: 7, Commit: "bbbbbbbbbbbb0123456789"}
+	builds := []link.CheckBuild{{Module: "app"}}
+	if got := namedForTheCheck(t.Context(), p, builds); !reflect.DeepEqual(got, []link.CheckedBuild{mine}) ||
+		!reflect.DeepEqual(asked, [][]link.PullRef{{pull}}) {
+		t.Fatalf("the check is handed %+v, read for %v", got, asked)
 	}
-	checkedBuildsOfModules = func(context.Context, []string) ([]link.CheckedBuild, error) {
+	checkedBuildsOf = func(context.Context, []link.PullRef) ([]link.CheckedBuild, error) {
 		return nil, errors.New("no bus")
 	}
-	if got := namedForTheCheck(t.Context(), builds); got != nil {
+	if got := namedForTheCheck(t.Context(), p, builds); got != nil {
 		t.Fatalf("verdicts that could not be read named %+v", got)
 	}
 }
+
+func forgetWalkVerdicts() {
+	walkVerdicts.Lock()
+	defer walkVerdicts.Unlock()
+	walkVerdicts.read = map[string]verdictsRead{}
+}

cmd/mesh-controller/checks.go

@@ -283,30 +283,32 @@ func checkRequestFor(ctx context.Context, open *stores, p link.PullUpdated, scop
 		Source:     sourceOnSeat(source),
 		Check: &link.CheckRequest{Owner: p.Owner, Repo: p.Repo, Number: p.Number, Base: p.Base,
 			Paths: p.Paths, Beside: beside, Modules: scope.Modules, Dependents: scope.Dependents, New: scope.New,
-			Manifests: scope.Manifests, Judge: scope.Judge, Builds: builds, Named: namedForTheCheck(ctx, builds)},
+			Manifests: scope.Manifests, Judge: scope.Judge, Builds: builds, Named: namedForTheCheck(ctx, p, builds)},
 	}, nil
 }
 
-// namedForTheCheck are the builds the seat's verdicts name for the modules a check builds, read once for the check
-// (novox/hq issue 703): what it may keep instead of building again. None when they cannot be read, and the check
-// builds, as before.
-func namedForTheCheck(ctx context.Context, builds []link.CheckBuild) []link.CheckedBuild {
-	var modules []string
-	for _, b := range builds {
-		if b.Skip == "" {
-			modules = append(modules, b.Module)
-		}
-	}
-	if len(modules) == 0 {
+// namedForTheCheck are the builds earlier checks of the same pull request at the same head named, read once for the
+// check (novox/hq issue 703): asked again because only the trunk moved, the check keeps what they built of a key
+// still the same. Another pull request's build, or one of an earlier head, is never kept. None when they cannot be
+// read, and the check builds, as before.
+func namedForTheCheck(ctx context.Context, p link.PullUpdated, builds []link.CheckBuild) []link.CheckedBuild {
+	if len(builds) == 0 || p.Commit == "" {
 		return nil
 	}
-	named, err := checkedBuildsOfModules(ctx, modules)
+	pull := link.PullRef{Owner: p.Owner, Repo: p.Repo, Number: p.Number}
+	read, err := checkedBuildsOf(ctx, []link.PullRef{pull})
 	if err != nil {
-		fmt.Printf("  the checks' builds of %d module(s) could not be read, so the check builds them: %v\n",
-			len(modules), err)
+		fmt.Printf("  the earlier checks' builds of %s/%s#%d could not be read, so the check builds: %v\n",
+			p.Owner, p.Repo, p.Number, err)
 		// empty-on-error: said above; a check handed no named build builds every module, as before issue 703
 		return nil
 	}
+	var named []link.CheckedBuild
+	for _, b := range read {
+		if b.Pull == pull && link.SameHead(b.Head, p.Commit) {
+			named = append(named, b)
+		}
+	}
 	return named
 }
 

cmd/mesh-controller/release_plan.go

@@ -9,6 +9,7 @@ import (
 	"slices"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/nats-io/nats.go"
@@ -386,30 +387,73 @@ var checkedBuildsOf = func(ctx context.Context, pulls []link.PullRef) ([]link.Ch
 	return link.ReadCheckBuilds(ctx, js, buildSeatHeld(ctx), pulls, time.Now().Add(-builder.CheckBuildsKept))
 }
 
-// checkedBuildsOfModules are the builds the build seat's checks of any pull request said they made, or kept, of
-// those modules within the week check builds are kept (novox/hq issue 703): what a check may keep instead of
-// building. A variable so a test needs no bus.
-var checkedBuildsOfModules = func(ctx context.Context, modules []string) ([]link.CheckedBuild, error) {
-	if len(modules) == 0 {
-		return nil, nil
+// mergedHeadsOf are the head commits the walk's merges merged, by pull request (novox/hq issue 703): a pull request
+// merged twice in one walk, or whose head the announcement did not say, has none, and takes no check's build.
+func mergedHeadsOf(p *inventory.Plan) map[link.PullRef]string {
+	heads := map[link.PullRef]string{}
+	if p.Delivery == nil {
+		return heads
 	}
-	js, err := aBus()
-	if err != nil {
-		return nil, err
+	seen := map[link.PullRef]bool{}
+	for _, m := range p.Delivery.Merges {
+		pull, ok := pullOf(m)
+		if !ok {
+			continue
+		}
+		if seen[pull] && heads[pull] != m.Head {
+			heads[pull] = ""
+			continue
+		}
+		seen[pull] = true
+		heads[pull] = m.Head
 	}
-	defer js.Close()
-	return link.ReadCheckBuildsOf(ctx, js, buildSeatHeld(ctx), modules, time.Now().Add(-builder.CheckBuildsKept))
+	return heads
+}
+
+// walkVerdicts are the checks' builds a walk read, by the walk's plan: read once per walk (novox/hq issue 649), not
+// once per module it asks for. Kept a day; a walk lasts minutes.
+var walkVerdicts = struct {
+	sync.Mutex
+	read map[string]verdictsRead
+}{read: map[string]verdictsRead{}}
+
+type verdictsRead struct {
+	at     time.Time
+	builds []link.CheckedBuild
 }
 
 // reuseWithVerdicts is a walk's leave with the builds its pull requests' verdicts name: the only builds the builder
-// may take (ADR 0350 §2). When they cannot be read the leave names none, and the walk builds, saying why.
-func reuseWithVerdicts(ctx context.Context, r *link.ReuseAsk) *link.ReuseAsk {
-	builds, err := checkedBuildsOf(ctx, r.Pulls)
-	if err != nil {
-		fmt.Printf("  the checks' builds of %d pull request(s) could not be read, so the walk builds: %v\n", len(r.Pulls), err)
-		return r
+// may take (ADR 0350 §2), and **only those of a check of the head each merge merged** (novox/hq issue 703): a build
+// a check made at an earlier head of the same pull request is never registered. Read once per walk. When they
+// cannot be read the leave names none, and the walk builds, saying why.
+func reuseWithVerdicts(ctx context.Context, walk string, r *link.ReuseAsk, heads map[link.PullRef]string) *link.ReuseAsk {
+	walkVerdicts.Lock()
+	read, known := walkVerdicts.read[walk]
+	walkVerdicts.Unlock()
+	if !known || walk == "" {
+		builds, err := checkedBuildsOf(ctx, r.Pulls)
+		if err != nil {
+			fmt.Printf("  the checks' builds of %d pull request(s) could not be read, so the walk builds: %v\n", len(r.Pulls), err)
+			return r
+		}
+		read = verdictsRead{at: time.Now(), builds: builds}
+		if walk != "" {
+			walkVerdicts.Lock()
+			for id, w := range walkVerdicts.read {
+				if time.Since(w.at) > 24*time.Hour {
+					delete(walkVerdicts.read, id)
+				}
+			}
+			walkVerdicts.read[walk] = read
+			walkVerdicts.Unlock()
+		}
+	}
+	r.Builds = nil
+	for _, b := range read.builds {
+		if link.SameHead(b.Head, heads[b.Pull]) {
+			r.Builds = append(r.Builds, b)
+		}
 	}
-	r.Builds = builds
 	return r
 }
 
@@ -452,7 +496,8 @@ func askModule(ctx context.Context, p *inventory.Plan, name string, byName map[s
 	}
 	// **The walk takes the check's build of the same key** (novox/hq ADR 0350 §2): its ask says so, with the pull
 	// requests it answers, whose checks name the part of a differing key.
-	id, err := askABuild(withReuse(ctx, reuseWithVerdicts(ctx, reuseAskOf(p))), source, e.Source.Path, ref)
+	id, err := askABuild(withReuse(ctx, reuseWithVerdicts(ctx, p.ID, reuseAskOf(p), mergedHeadsOf(p))), source,
+		e.Source.Path, ref)
 	if err != nil {
 		state.State = "failed"
 		state.Why = err.Error()