builder-next: ensure timestamps set for metadata commands

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

builder/builder-next/exporter/writer.go

@@ -137,6 +137,37 @@ func normalizeLayersAndHistory(diffs []digest.Digest, history []ocispec.History,
 		history[i] = h
 	}
 
+	// Find the first new layer time. Otherwise, the history item for a first
+	// metadata command would be the creation time of a base image layer.
+	// If there is no such then the last layer with timestamp.
+	var created *time.Time
+	var noCreatedTime bool
+	for _, h := range history {
+		if h.Created != nil {
+			created = h.Created
+			if noCreatedTime {
+				break
+			}
+		} else {
+			noCreatedTime = true
+		}
+	}
+
+	// Fill in created times for all history items to be either the first new
+	// layer time or the previous layer.
+	noCreatedTime = false
+	for i, h := range history {
+		if h.Created != nil {
+			if noCreatedTime {
+				created = h.Created
+			}
+		} else {
+			noCreatedTime = true
+			h.Created = created
+		}
+		history[i] = h
+	}
+
 	return diffs, history
 }