Tell a rebuild that changes nothing by its artifacts and its manifest (hq ADR 0236)

cmd/mesh-controller/bus_step.go

@@ -54,13 +54,13 @@ type busPending struct {
 	machines []string
 	from     map[string]string
 	to       string
-	// same are the commits whose build made the same artifacts as the build the mesh holds.
+	// same are the commits whose build made the same artifacts and manifest as the build the mesh holds.
 	same map[string]bool
 }
 
 // moves is whether sending the machine would replace its bus: a build it was not last sent, unless the
-// two builds made the same artifacts — a rebuild of the same source for another module's merge changes
-// nothing the machine runs.
+// two builds made the same artifacts from the same manifest — a rebuild of the same source for another
+// module's merge changes nothing the machine runs.
 func (b busPending) moves(machine string) bool {
 	from, known := b.from[machine]
 	if b.module == "" || b.to == "" || (known && sameCommit(from, b.to)) {
@@ -93,7 +93,7 @@ func pendingBus(ctx context.Context, inv *inventory.Inventory) (busPending, erro
 		return b, err
 	}
 	b.from, b.same = map[string]string{}, map[string]bool{}
-	made, err := madeBy(ctx, inv, b.module)
+	made, err := inv.BuildFingerprints(ctx, b.module)
 	if err != nil {
 		return b, err
 	}
@@ -397,28 +397,3 @@ func withBusStep(ctx context.Context) context.Context {
 }
 
 func busStepSending(ctx context.Context) bool { on, _ := ctx.Value(busStepKey{}).(bool); return on }
-
-// madeBy is, per commit, the artifacts the newest worked build of a module from it made, as one sorted
-// string: what tells a rebuild that changes nothing from one that does.
-func madeBy(ctx context.Context, inv *inventory.Inventory, module string) (map[string]string, error) {
-	builds, err := inv.Builds(ctx, module, 50)
-	if err != nil {
-		return nil, err
-	}
-	out := map[string]string{}
-	for _, b := range builds {
-		if !b.Worked() || b.Commit == "" {
-			continue
-		}
-		if _, seen := out[b.Commit]; seen {
-			continue
-		}
-		var refs []string
-		for _, a := range b.Made {
-			refs = append(refs, a.Name+"="+a.Reference)
-		}
-		sort.Strings(refs)
-		out[b.Commit] = strings.Join(refs, " ")
-	}
-	return out, nil
-}

internal/inventory/gate.go

@@ -2,6 +2,8 @@ package inventory
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -216,3 +218,30 @@ func (i *Inventory) RestoreModule(ctx context.Context, b Build) error {
 	}
 	return nil
 }
+
+// BuildFingerprints is, per commit, what the newest successful build of a module from it would put on a
+// machine — its artifacts and its manifest, hashed — so a rebuild that changes nothing there is told
+// from one that does (the bus's planned step, ADR 0236).
+func (i *Inventory) BuildFingerprints(ctx context.Context, module string) (map[string]string, error) {
+	rows, err := i.store.Pool().Query(ctx,
+		`select commit_hash, made, coalesce(manifest::text, '') from build
+		  where module = $1 and failed = '' and commit_hash <> '' order by at desc limit 50`, module)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := map[string]string{}
+	for rows.Next() {
+		var commit, manifest string
+		var made []byte
+		if err := rows.Scan(&commit, &made, &manifest); err != nil {
+			return nil, err
+		}
+		if _, seen := out[commit]; seen {
+			continue
+		}
+		sum := sha256.Sum256(append(append(made, 0), []byte(manifest)...))
+		out[commit] = hex.EncodeToString(sum[:])
+	}
+	return out, rows.Err()
+}