cue/literal: use strconv.IsGraphic

This code was a direct copy of strconv.IsGraphic with no changes,
so there isn't a need to duplicate it.
We already used strconv.IsPrint in this Go file,
and we already used both APIs in other Go packages in our module.

While here, as suggested by Matthew, use parentheses to make the
boolean logic clear with respect to operator precedence.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I4d4f6416e8a265fee89b3ed357fdb3d4771d0e7f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1198060
Reviewed-by: Matthew Sackman <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

cue/literal/quote.go

@@ -234,7 +234,7 @@ func (f *Form) appendEscapedRune(buf []byte, r rune) []byte {
 			buf = append(buf, byte(r))
 			return buf
 		}
-	} else if strconv.IsPrint(r) || f.graphicOnly && isInGraphicList(r) {
+	} else if strconv.IsPrint(r) || (f.graphicOnly && strconv.IsGraphic(r)) {
 		buf = utf8.AppendRune(buf, r)
 		return buf
 	}
@@ -319,51 +319,3 @@ func (f *Form) requiredHashCount(s string) int {
 	}
 	return hashCount
 }
-
-// isInGraphicList reports whether the rune is in the isGraphic list. This separation
-// from IsGraphic allows quoteWith to avoid two calls to IsPrint.
-// Should be called only if IsPrint fails.
-func isInGraphicList(r rune) bool {
-	// We know r must fit in 16 bits - see makeisprint.go.
-	if r > 0xFFFF {
-		return false
-	}
-	rr := uint16(r)
-	i := bsearch16(isGraphic, rr)
-	return i < len(isGraphic) && rr == isGraphic[i]
-}
-
-// bsearch16 returns the smallest i such that a[i] >= x.
-// If there is no such i, bsearch16 returns len(a).
-func bsearch16(a []uint16, x uint16) int {
-	i, j := 0, len(a)
-	for i < j {
-		h := i + (j-i)/2
-		if a[h] < x {
-			i = h + 1
-		} else {
-			j = h
-		}
-	}
-	return i
-}
-
-// isGraphic lists the graphic runes not matched by IsPrint.
-var isGraphic = []uint16{
-	0x00a0,
-	0x1680,
-	0x2000,
-	0x2001,
-	0x2002,
-	0x2003,
-	0x2004,
-	0x2005,
-	0x2006,
-	0x2007,
-	0x2008,
-	0x2009,
-	0x200a,
-	0x202f,
-	0x205f,
-	0x3000,
-}