Format Strings outside Printf

If you declare format strings for Printf-style functions outside a stringliteral, make them const values.

This helps go vet perform static analysis of the format string.

BadGood
  1. msg := "unexpected values %v, %v\n"
  2. fmt.Printf(msg, 1, 2)
 
  1. const msg = "unexpected values %v, %v\n"
  2. fmt.Printf(msg, 1, 2)