fmt: fix formatting of numbers with f.space and f.plus specified

Do not replace the sign in front of a number with a space if both
f.space and f.plus are both specified for number formatting.
This was already the case for integers but not for floats
and complex numbers.

Updates: #14543.

Change-Id: I07ddeb505003db84a8a7d2c743dc19fc427a00bd
Reviewed-on: https://go-review.googlesource.com/19974
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

@@ -278,6 +278,9 @@ var fmtTests = []struct {
 	{"%b", 1.0, "4503599627370496p-52"},
 
 	// complex values
+	{"%.f", 0i, "(0+0i)"},
+	{"%+.f", 0i, "(+0+0i)"},
+	{"% +.f", 0i, "(+0+0i)"},
 	{"%+.3e", 0i, "(+0.000e+00+0.000e+00i)"},
 	{"%+.3f", 0i, "(+0.000+0.000i)"},
 	{"%+.3g", 0i, "(+0+0i)"},
@@ -384,9 +387,13 @@ var fmtTests = []struct {
 	{"%g", 1.23456789e-3, "0.00123456789"},
 	{"%g", 1.23456789e20, "1.23456789e+20"},
 	{"%20e", math.Inf(1), "                +Inf"},
+	{"% 20f", math.Inf(1), "                 Inf"},
+	{"%+20f", math.Inf(1), "                +Inf"},
+	{"% +20f", math.Inf(1), "                +Inf"},
 	{"%-20f", math.Inf(-1), "-Inf                "},
 	{"%20g", math.NaN(), "                 NaN"},
 	{"%+20f", math.NaN(), "                +NaN"},
+	{"% +20f", math.NaN(), "                +NaN"},
 	{"% -20f", math.NaN(), " NaN                "},
 	{"%+-20f", math.NaN(), "+NaN                "},
 
@@ -608,14 +615,16 @@ var fmtTests = []struct {
 			"[%7.2f]",
 			"[% 7.2f]",
 			"[%+7.2f]",
+			"[% +7.2f]",
 			"[%07.2f]",
 			"[% 07.2f]",
 			"[%+07.2f]",
+			"[% +07.2f]"
 		};
 
 		int main(void) {
 			int i;
-			for(i = 0; i < 9; i++) {
+			for(i = 0; i < 11; i++) {
 				printf("%s: ", format[i]);
 				printf(format[i], 1.0);
 				printf(" ");
@@ -631,9 +640,12 @@ var fmtTests = []struct {
 			[%7.2f]: [   1.00] [  -1.00]
 			[% 7.2f]: [   1.00] [  -1.00]
 			[%+7.2f]: [  +1.00] [  -1.00]
+			[% +7.2f]: [  +1.00] [  -1.00]
 			[%07.2f]: [0001.00] [-001.00]
 			[% 07.2f]: [ 001.00] [-001.00]
 			[%+07.2f]: [+001.00] [-001.00]
+			[% +07.2f]: [+001.00] [-001.00]
+
 	*/
 	{"%.2f", 1.0, "1.00"},
 	{"%.2f", -1.0, "-1.00"},
@@ -647,12 +659,16 @@ var fmtTests = []struct {
 	{"% 7.2f", -1.0, "  -1.00"},
 	{"%+7.2f", 1.0, "  +1.00"},
 	{"%+7.2f", -1.0, "  -1.00"},
+	{"% +7.2f", 1.0, "  +1.00"},
+	{"% +7.2f", -1.0, "  -1.00"},
 	{"%07.2f", 1.0, "0001.00"},
 	{"%07.2f", -1.0, "-001.00"},
 	{"% 07.2f", 1.0, " 001.00"},
 	{"% 07.2f", -1.0, "-001.00"},
 	{"%+07.2f", 1.0, "+001.00"},
 	{"%+07.2f", -1.0, "-001.00"},
+	{"% +07.2f", 1.0, "+001.00"},
+	{"% +07.2f", -1.0, "-001.00"},
 
 	// Complex numbers: exhaustively tested in TestComplexFormatting.
 	{"%7.2f", 1 + 2i, "(   1.00  +2.00i)"},

src/fmt/format.go

@@ -390,8 +390,9 @@ func (f *fmt) formatFloat(v float64, verb byte, prec, n int) {
 	} else {
 		num[0] = '+'
 	}
-	// f.space says to replace a leading + with a space.
-	if f.space && num[0] == '+' {
+	// f.space means to add a leading space instead of a "+" sign unless
+	// the sign is explicitly asked for by f.plus.
+	if f.space && num[0] == '+' && !f.plus {
 		num[0] = ' '
 	}
 	// Special handling for infinities and NaN,