Prealloc confused by variable redeclaration

[rgeronimi]

In the following function, prealloc is confused by buf being redeclared:

func copySort(w io.Writer, r io.Reader, sep rune, keys []int) error {
	// Copy the header line.
	var buf [1]byte // THATS LINE 275 WHERE THE ERROR MESSAGES POINT TO
	for {
		n, err := r.Read(buf[:])
		if n != 0 {
			if _, err := w.Write(buf[:]); err != nil {
				return err
			}
		}
		if err != nil {
			if err == io.EOF {
				return nil
			}
			return err
		}
		if buf[0] == '\n' {
			break
		}
	}
	...
	for i, k := range keys {
		buf := make([]byte, 0, 16)
		buf = append(buf, "-k"...)
		n := int64(1 + k)
		buf = strconv.AppendInt(buf, n, 10)
		buf = append(buf, ',')
		buf = strconv.AppendInt(buf, n, 10)
		args[2+i] = alloc.DirectString(buf)
	}
	...
}

preallocreports these 2 error messages:

...:275 Consider preallocating buf
...:275 Consider preallocating buf

If I rename the first buf declaration with any other variable name (e.g., cell) the error messages disappear.

It seems a variable redeclaration is not always managed correctly by prealloc.

[alexkohler]

Interesting.. I'll try to look into this ASAP.