This has changed because of a change in the status of the Unicode code point \u9fe5. In Go 1.9 strconv.IsPrint('\u9fe5') returns false. In 1.10 and 1.11 it returns true. This changes the behavior of strconv.Quote, which changes the behavior of the %q used by the Generate function being tested.

The change to strconv.Quote happened in https://golang.org/cl/63953, which updated the package to Unicode 10.0.0

I think if we want this test to be stable across Go releases we should not be using %q to print non-string data.

CC @agnivade

Thanks for the analysis @ianlancetaylor. I believe you are talking about this part of the code -

if utf8.Valid(b) {
	fmt.Fprintf(buf, "`%s`", sanitize(b))
} else {
	fmt.Fprintf(buf, "%q", b)
}

What do you suggest we do instead of %q ? Because we anyways have to quote the output.

I think if we are to simply use %s, there is some more sanitization that needs to be done. Trying to print with `%s`, it throws an illegal UTF-8 encoding error. ping @bradfitz who probably wrote/reviewed the sanitize function.

Or should we maintain per-release copies of static.go and delete it once 1.11 is released ?

Change https://golang.org/cl/118955 mentions this issue: godoc/static: mimic the pre-1.10 behavior of strconv.Quote