encoding/json: marshal maps using reflect.Value.MapRange

Map serialization using reflect.Value.MapIndex cannot retrieve
map keys that contain a NaN, resulting in a panic.
Switch the implementation to use the reflect.Value.MapRange method
instead, which iterates over all map entries regardless of whether
they are directly retrievable.

Note that according to RFC 8259, section 4, a JSON object should
have unique names, but does not forbid the occurrence of duplicate names.

Fixes #43207

Change-Id: If4bc55229b1f64b8ca4b0fed37549725efdace39
Reviewed-on: https://go-review.googlesource.com/c/go/+/278632
Trust: Meng Zhuo <mzh@golangcn.org>
Trust: Joe Tsai <thebrokentoaster@gmail.com>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Meng Zhuo <mzh@golangcn.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/encoding/json/encode_test.go b/src/encoding/json/encode_test.go
index 42bb09d5cd..0dad951095 100644
--- a/src/encoding/json/encode_test.go
+++ b/src/encoding/json/encode_test.go
@@ -245,6 +245,22 @@ func TestUnsupportedValues(t *testing.T) {
 	}
 }
 
+// Issue 43207
+func TestMarshalTextFloatMap(t *testing.T) {
+	m := map[textfloat]string{
+		textfloat(math.NaN()): "1",
+		textfloat(math.NaN()): "1",
+	}
+	got, err := Marshal(m)
+	if err != nil {
+		t.Errorf("Marshal() error: %v", err)
+	}
+	want := `{"TF:NaN":"1","TF:NaN":"1"}`
+	if string(got) != want {
+		t.Errorf("Marshal() = %s, want %s", got, want)
+	}
+}
+
 // Ref has Marshaler and Unmarshaler methods with pointer receiver.
 type Ref int
 
@@ -854,6 +870,10 @@ func tenc(format string, a ...interface{}) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
+type textfloat float64
+
+func (f textfloat) MarshalText() ([]byte, error) { return tenc(`TF:%0.2f`, f) }
+
 // Issue 13783
 func TestEncodeBytekind(t *testing.T) {
 	testdata := []struct {
@@ -872,6 +892,7 @@ func TestEncodeBytekind(t *testing.T) {
 		{[]jsonint{5, 4}, `[{"JI":5},{"JI":4}]`},
 		{[]textint{9, 3}, `["TI:9","TI:3"]`},
 		{[]int{9, 3}, `[9,3]`},
+		{[]textfloat{12, 3}, `["TF:12.00","TF:3.00"]`},
 	}
 	for _, d := range testdata {
 		js, err := Marshal(d.data)