fmt: clear flags before printing extra argument errors

Do a reset of the fmt flags before printing the extra argument
error message to prevent a malformed printing of extra arguments.

Regroup tests for extra argument error strings.

Change-Id: Ifd97f5ca36f6c97ed5a380d975cf154d17997d3f
Reviewed-on: https://go-review.googlesource.com/20571
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/fmt/fmt_test.go

@@ -426,10 +426,6 @@ var fmtTests = []struct {
 	{"%-08g", complex(negInf, negInf), "(-Inf    -Inf    i)"},
 	{"%-08G", complex(NaN, NaN), "(NaN     +NaN    i)"},
 
-	// erroneous formats
-	{"", 2, "%!(EXTRA int=2)"},
-	{"%d", "hello", "%!d(string=hello)"},
-
 	// old test/fmt_test.go
 	{"%d", 1234, "1234"},
 	{"%d", -1234, "-1234"},
@@ -774,15 +770,15 @@ var fmtTests = []struct {
 	{"%d", time.Time{}.Month(), "1"},
 
 	// erroneous things
+	{"", nil, "%!(EXTRA <nil>)"},
+	{"", 2, "%!(EXTRA int=2)"},
+	{"no args", "hello", "no args%!(EXTRA string=hello)"},
 	{"%s %", "hello", "hello %!(NOVERB)"},
 	{"%s %.2", "hello", "hello %!(NOVERB)"},
-	{"%d", "hello", "%!d(string=hello)"},
-	{"no args", "hello", "no args%!(EXTRA string=hello)"},
-	{"%s", nil, "%!s(<nil>)"},
-	{"%T", nil, "<nil>"},
-	{"%-1", 100, "%!(NOVERB)%!(EXTRA int=100)"},
 	{"%017091901790959340919092959340919017929593813360", 0, "%!(NOVERB)%!(EXTRA int=0)"},
 	{"%184467440737095516170v", 0, "%!(NOVERB)%!(EXTRA int=0)"},
+	// Extra argument errors should format without flags set.
+	{"%010.2", "12345", "%!(NOVERB)%!(EXTRA string=12345)"},
 
 	// The "<nil>" show up because maps are printed by
 	// first obtaining a list of keys and then looking up
@@ -973,6 +969,7 @@ var fmtTests = []struct {
 	{"%☠", []uint8{0}, "%!☠([]uint8=[0])"},
 	{"%☠", [1]byte{0}, "%!☠([1]uint8=[0])"},
 	{"%☠", [1]uint8{0}, "%!☠([1]uint8=[0])"},
+	{"%☠", "hello", "%!☠(string=hello)"},
 	{"%☠", 1.2345678, "%!☠(float64=1.2345678)"},
 	{"%☠", float32(1.2345678), "%!☠(float32=1.2345678)"},
 	{"%☠", 1.2345678 + 1.2345678i, "%!☠(complex128=(1.2345678+1.2345678i))"},

src/fmt/print.go

@@ -1164,8 +1164,6 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 			p.buf.WriteString(missingString)
 			continue
 		}
-		arg := a[argNum]
-		argNum++
 
 		if c == 'v' {
 			if p.fmt.sharp {
@@ -1185,23 +1183,26 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 			p.fmt.zero = false
 		}
 
-		p.printArg(arg, c, 0)
+		p.printArg(a[argNum], c, 0)
+		argNum++
 	}
 
 	// Check for extra arguments unless the call accessed the arguments
 	// out of order, in which case it's too expensive to detect if they've all
 	// been used and arguably OK if they're not.
 	if !p.reordered && argNum < len(a) {
+		p.fmt.clearflags()
 		p.buf.WriteString(extraString)
-		for ; argNum < len(a); argNum++ {
-			arg := a[argNum]
-			if arg != nil {
+		for i, arg := range a[argNum:] {
+			if i > 0 {
+				p.buf.WriteString(commaSpaceString)
+			}
+			if arg == nil {
+				p.buf.WriteString(nilAngleString)
+			} else {
 				p.buf.WriteString(reflect.TypeOf(arg).String())
 				p.buf.WriteByte('=')
-			}
 				p.printArg(arg, 'v', 0)
-			if argNum+1 < len(a) {
-				p.buf.WriteString(commaSpaceString)
 			}
 		}
 		p.buf.WriteByte(')')