fmt: avoid badverb formatting for %q when used with integers

Instead of returning a bad verb error format for runes above
utf8.Maxrune return a quoted utf8.RuneError rune (\ufffd).
This makes the behaviour consistent with the "c" verb and
aligns behaviour to not return bad verb error format when
a verb is applied to the correct argument type.

Fixes #14569

Change-Id: I679485f6bb90ebe408423ab68af16cce38816cd0
Reviewed-on: https://go-review.googlesource.com/c/go/+/248759
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/fmt/fmt_test.go

@@ -290,11 +290,11 @@ var fmtTests = []struct {
 	{"%q", '\U00000e00', `'\u0e00'`},
 	{"%q", '\U0010ffff', `'\U0010ffff'`},
 	// Runes that are not valid.
-	{"%q", int32(-1), "%!q(int32=-1)"},
+	{"%q", int32(-1), `'�'`},
 	{"%q", 0xDC80, `'�'`},
-	{"%q", rune(0x110000), "%!q(int32=1114112)"},
-	{"%q", int64(0xFFFFFFFFF), "%!q(int64=68719476735)"},
-	{"%q", uint64(0xFFFFFFFFF), "%!q(uint64=68719476735)"},
+	{"%q", rune(0x110000), `'�'`},
+	{"%q", int64(0xFFFFFFFFF), `'�'`},
+	{"%q", uint64(0xFFFFFFFFF), `'�'`},
 
 	// width
 	{"%5s", "abc", "  abc"},

src/fmt/print.go

@@ -388,11 +388,7 @@ func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
 	case 'c':
 		p.fmt.fmtC(v)
 	case 'q':
-		if v <= utf8.MaxRune {
-			p.fmt.fmtQc(v)
-		} else {
-			p.badVerb(verb)
-		}
+		p.fmt.fmtQc(v)
 	case 'U':
 		p.fmt.fmtUnicode(v)
 	default: