This is meant to share my progress on Issue 8275, if it's useful to you. I'm not familiar with the formatter's internals, so this change is likely naive.

Change these calls to measure width in runes not bytes:
fmt.Printf("(%5q)\n", '§')
fmt.Printf("(%3c)\n", '§')

 Fixes #8275.

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/104320043