by kwalsh@holycross.edu:

What does 'go version' print? go version go1.3 linux/amd64

What steps reproduce the problem?

Example here: http://play.golang.org/p/H-KFkROfOJ
1. Call fmt.Sscanf("Hello", "%s", &x) where x implements Scanner.
2. Within x's Scan() function, call r, n, err := state.ReadRune().

What happened?
ReadRune() returns 'H', 0, nil

What should have happened instead?
ReadRune() should have returned 'H', 1, nil

Please provide any additional information below.
pkg/fmt/scan.go contains this code:
   356  func (r *readRune) ReadRune() (rr rune, size int, err error) {
   357      r.buf[0], err = r.readByte()
   358      if err != nil {
   359          return 0, 0, err
   360      }
   361      if r.buf[0] < utf8.RuneSelf { // fast check for common ASCII case
   362          rr = rune(r.buf[0])
   363          return
   364      }
The fast case needs to set the size, e.g.:
   size = utf8.RuneLen(rr)