NEW FEATURE: diff2: A better "diff" mechanism (#1852)

pkg/diff2/nopurge.go

@@ -0,0 +1,22 @@
+package diff2
+
+func processPurge(instructions ChangeList, nopurge bool) ChangeList {
+
+	if nopurge {
+		return instructions
+	}
+
+	// TODO(tlim): This can probably be done without allocations but it
+	// works and I won't want to prematurely optimize.
+
+	newinstructions := make(ChangeList, 0, len(instructions))
+	for _, j := range instructions {
+		if j.Type == DELETE {
+			continue
+		}
+		newinstructions = append(newinstructions, j)
+	}
+
+	return newinstructions
+
+}