Leave a module out of a send when the store lacks its image, and say it (issue 1742)

internal/builder/registry.go

@@ -59,15 +59,35 @@ func (r Registry) PublishImage(ctx context.Context, localTag, repository string)
 	}); err != nil {
 		return "", err
 	}
-	out, err := r.Run(ctx, "", "docker", "inspect", "--format", "{{index .RepoDigests 0}}", remote)
+	// Every digest the daemon lists for the image, one per line: the image may have been pushed under other names before
+	// (a check's scratch copy, another registry), and the first of them is not the one this push made (novox/hq issue
+	// 1742: a build recorded a digest the store never held).
+	out, err := r.Run(ctx, "", "docker", "inspect", "--format", "{{range .RepoDigests}}{{println .}}{{end}}", remote)
 	if err != nil {
 		return "", fmt.Errorf("pushed %s and cannot read back what it was pinned as: %w", remote, err)
 	}
-	pinned := strings.TrimSpace(out)
-	if !strings.Contains(pinned, "@sha256:") {
+	first, pinned := "", ""
+	for _, line := range strings.Split(out, "\n") {
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+		if first == "" {
+			first = line
+		}
+		if strings.HasPrefix(line, remote+"@sha256:") {
+			pinned = line
+			break
+		}
+	}
+	if pinned == "" {
+		if strings.Contains(first, "@sha256:") {
+			return "", fmt.Errorf("pushed %s, but the daemon lists no digest for that name (only %q): the digest of another "+
+				"repository is not what this registry serves", remote, first)
+		}
 		// A tag is not a pin. It can be made to point at something else, and this file is applied
 		// on machines with no mesh to ask about anything (novox/hq ADR 0006).
-		return "", fmt.Errorf("%s came back as %q, which is not pinned by digest", remote, pinned)
+		return "", fmt.Errorf("%s came back as %q, which is not pinned by digest", remote, first)
 	}
 	return pinned, nil
 }