Function RegisterTypeMigration

errbase/migrations.go:94–112

This file provides the library with the ability to handle cases where an error type migrates, i.e. its package changes path or the type name is changed. There are several scenarios to contend with. Assuming the error type is initially called "foo", in version v1 of the code. Scenario 1: simple mig

(previousPkgPath, previousTypeName string, newType error)

// the last component of the package path can be different. This is
// why they must be specified separately.
func RegisterTypeMigration(previousPkgPath, previousTypeName string, newType error) {
	prevKey := TypeKey(makeTypeKey(previousPkgPath, previousTypeName))
	newKey := TypeKey(getFullTypeName(newType))

	// Register the backward migration: make the encode function
	// aware of the old name.
	if f, ok := backwardRegistry[newKey]; ok {
		panic(fmt.Errorf("migration to type %q already registered (from %q)", newKey, f))
	}
	backwardRegistry[newKey] = prevKey
	// If any other key was registered as a migration from newKey,
	// we'll forward those as well.
	// This changes X -> newKey to X -> prevKey for every X.
	for new, prev := range backwardRegistry {
		if prev == newKey {
			backwardRegistry[new] = prevKey
		}
	}
}

// registry used when encoding an error, so that the receiver observes
// the original key. This maps new keys to old keys.