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

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()
+}