db: implement fmt.Stringer on BackingType

This will be used within Cockroach to implement a custom JSON serialization of
the set of sstables returned by the sstable_metrics builtin.

db.go

@@ -2098,8 +2098,21 @@ const (
  // or lifecycle management. An example of an external file is a file restored
  // from a backup.
  BackingTypeExternal
+ backingTypeCount
 )
 
+var backingTypeToString = [backingTypeCount]string{
+ BackingTypeLocal: "local",
+ BackingTypeShared: "shared",
+ BackingTypeSharedForeign: "shared-foreign",
+ BackingTypeExternal: "external",
+}
+
+// String implements fmt.Stringer.
+func (b BackingType) String() string {
+ return backingTypeToString[b]
+}
+
 // SSTableInfo export manifest.TableInfo with sstable.Properties alongside
 // other file backing info.
 type SSTableInfo struct {