fmt: make %#p suppress leading 0x

Fixes bug 1567.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4245048

src/pkg/fmt/fmt_test.go

@@ -311,9 +311,9 @@ var fmttests = []struct {
 
 	// go syntax
 	{"%#v", A{1, 2, "a", []int{1, 2}}, `fmt_test.A{i:1, j:0x2, s:"a", x:[]int{1, 2}}`},
-	{"%#v", &b, "(*uint8)(PTR)"},
-	{"%#v", TestFmtInterface, "(func(*testing.T))(PTR)"},
-	{"%#v", make(chan int), "(chan int)(PTR)"},
+	{"%#v", &b, "(*uint8)(0xPTR)"},
+	{"%#v", TestFmtInterface, "(func(*testing.T))(0xPTR)"},
+	{"%#v", make(chan int), "(chan int)(0xPTR)"},
 	{"%#v", uint64(1<<64 - 1), "0xffffffffffffffff"},
 	{"%#v", 1000000000, "1000000000"},
 	{"%#v", map[string]int{"a": 1, "b": 2}, `map[string] int{"a":1, "b":2}`},
@@ -365,14 +365,15 @@ var fmttests = []struct {
 	{"%6T", &intVal, "  *int"},
 
 	// %p
-	{"p0=%p", new(int), "p0=PTR"},
+	{"p0=%p", new(int), "p0=0xPTR"},
 	{"p1=%s", &pValue, "p1=String(p)"}, // String method...
-	{"p2=%p", &pValue, "p2=PTR"},       // ... not called with %p
+	{"p2=%p", &pValue, "p2=0xPTR"},     // ... not called with %p
+	{"p4=%#p", new(int), "p4=PTR"},
 
 	// %p on non-pointers
-	{"%p", make(chan int), "PTR"},
-	{"%p", make(map[int]int), "PTR"},
-	{"%p", make([]int, 1), "PTR"},
+	{"%p", make(chan int), "0xPTR"},
+	{"%p", make(map[int]int), "0xPTR"},
+	{"%p", make([]int, 1), "0xPTR"},
 	{"%p", 27, "%!p(int=27)"}, // not a pointer at all
 
 	// erroneous things
@@ -388,8 +389,8 @@ var fmttests = []struct {
 func TestSprintf(t *testing.T) {
 	for _, tt := range fmttests {
 		s := Sprintf(tt.fmt, tt.val)
-		if i := strings.Index(s, "0x"); i >= 0 && strings.Contains(tt.out, "PTR") {
-			j := i + 2
+		if i := strings.Index(tt.out, "PTR"); i >= 0 {
+			j := i
 			for ; j < len(s); j++ {
 				c := s[j]
 				if (c < '0' || c > '9') && (c < 'a' || c > 'f') && (c < 'A' || c > 'F') {
@@ -399,6 +400,7 @@ func TestSprintf(t *testing.T) {
 			s = s[0:i] + "PTR" + s[j:]
 		}
 		if s != tt.out {
+			println(s, "XXX", tt.out)
 			if _, ok := tt.val.(string); ok {
 				// Don't requote the already-quoted strings.
 				// It's too confusing to read the errors.

src/pkg/fmt/print.go

@@ -348,11 +348,11 @@ func (p *pp) fmtInt64(v int64, verb int, value interface{}) {
 	}
 }
 
-// fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x by
-// temporarily turning on the sharp flag.
-func (p *pp) fmt0x64(v uint64) {
+// fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
+// not, as requested, by temporarily setting the sharp flag.
+func (p *pp) fmt0x64(v uint64, leading0x bool) {
 	sharp := p.fmt.sharp
-	p.fmt.sharp = true // turn on 0x
+	p.fmt.sharp = leading0x
 	p.fmt.integer(int64(v), 16, unsigned, ldigits)
 	p.fmt.sharp = sharp
 }
@@ -384,7 +384,7 @@ func (p *pp) fmtUint64(v uint64, verb int, goSyntax bool, value interface{}) {
 		p.fmt.integer(int64(v), 10, unsigned, ldigits)
 	case 'v':
 		if goSyntax {
-			p.fmt0x64(v)
+			p.fmt0x64(v, true)
 		} else {
 			p.fmt.integer(int64(v), 10, unsigned, ldigits)
 		}
@@ -534,11 +534,11 @@ func (p *pp) fmtPointer(field interface{}, value reflect.Value, verb int, goSynt
 		if u == 0 {
 			p.buf.Write(nilBytes)
 		} else {
-			p.fmt0x64(uint64(v.Get()))
+			p.fmt0x64(uint64(v.Get()), true)
 		}
 		p.add(')')
 	} else {
-		p.fmt0x64(uint64(u))
+		p.fmt0x64(uint64(u), !p.fmt.sharp)
 	}
 }
 
@@ -801,7 +801,7 @@ BigSwitch:
 			if v == 0 {
 				p.buf.Write(nilBytes)
 			} else {
-				p.fmt0x64(uint64(v))
+				p.fmt0x64(uint64(v), true)
 			}
 			p.buf.WriteByte(')')
 			break
@@ -810,7 +810,7 @@ BigSwitch:
 			p.buf.Write(nilAngleBytes)
 			break
 		}
-		p.fmt0x64(uint64(v))
+		p.fmt0x64(uint64(v), true)
 	case uintptrGetter:
 		p.fmtPointer(field, value, verb, goSyntax)
 	default: