Put json.Number encoding behind SetJsonNumber() switch

cmd/jsontoml/main.go

@@ -45,7 +45,6 @@ func convert(r io.Reader, w io.Writer) error {
 	var v interface{}
 
 	d := json.NewDecoder(r)
-	d.UseNumber()
 	err := d.Decode(&v)
 	if err != nil {
 		return err

cmd/jsontoml/main_test.go

@@ -25,7 +25,7 @@ func TestConvert(t *testing.T) {
   }
 }`,
 			expected: `[mytoml]
-a = 42
+a = 42.0
 `,
 		},
 		{

marshaler.go

@@ -42,6 +42,7 @@ type Encoder struct {
 	arraysMultiline bool
 	indentSymbol    string
 	indentTables    bool
+	jsonNumber      bool
 }
 
 // NewEncoder returns a new Encoder that writes to w.
@@ -88,6 +89,13 @@ func (enc *Encoder) SetIndentTables(indent bool) *Encoder {
 	return enc
 }
 
+// SetJsonNumber forces the encoder to serialize `json.Number` as a float or integer
+// instead of relying on TextMarshaler to emit a string.
+func (enc *Encoder) SetJsonNumber(indent bool) *Encoder {
+	enc.jsonNumber = indent
+	return enc
+}
+
 // Encode writes a TOML representation of v to the stream.
 //
 // If v cannot be represented to TOML it returns an error.
@@ -254,14 +262,16 @@ func (enc *Encoder) encode(b []byte, ctx encoderCtx, v reflect.Value) ([]byte, e
 	case LocalDateTime:
 		return append(b, x.String()...), nil
 	case json.Number:
-		if x == "" { /// Useful zero value.
-			return append(b, "0"...), nil
-		} else if v, err := x.Int64(); err == nil {
-			return enc.encode(b, ctx, reflect.ValueOf(v))
-		} else if f, err := x.Float64(); err == nil {
-			return enc.encode(b, ctx, reflect.ValueOf(f))
-		} else {
-			return nil, fmt.Errorf("toml: unable to convert %q to int64 or float64", x)
+		if enc.jsonNumber {
+			if x == "" { /// Useful zero value.
+				return append(b, "0"...), nil
+			} else if v, err := x.Int64(); err == nil {
+				return enc.encode(b, ctx, reflect.ValueOf(v))
+			} else if f, err := x.Float64(); err == nil {
+				return enc.encode(b, ctx, reflect.ValueOf(f))
+			} else {
+				return nil, fmt.Errorf("toml: unable to convert %q to int64 or float64", x)
+			}
 		}
 	}
 

marshaler_test.go

@@ -679,31 +679,6 @@ I = 42
 J = 42
 K = 42
 L = 2.2
-`,
-		},
-		{
-			desc: "json numbers",
-			v: struct {
-				A json.Number
-				B json.Number
-				C json.Number
-				D json.Number
-				E json.Number
-				F json.Number
-			}{
-				A: "1.1",
-				B: "42e-3",
-				C: "42",
-				D: "0",
-				E: "0.0",
-				F: "",
-			},
-			expected: `A = 1.1
-B = 0.042
-C = 42
-D = 0
-E = 0.0
-F = 0
 `,
 		},
 		{
@@ -973,6 +948,29 @@ func TestEncoderSetIndentSymbol(t *testing.T) {
 	assert.Equal(t, expected, w.String())
 }
 
+func TestEncoderSetJsonNumber(t *testing.T) {
+	var w strings.Builder
+	enc := toml.NewEncoder(&w)
+	enc.SetJsonNumber(true)
+	err := enc.Encode(map[string]interface{}{
+		"A": json.Number("1.1"),
+		"B": json.Number("42e-3"),
+		"C": json.Number("42"),
+		"D": json.Number("0"),
+		"E": json.Number("0.0"),
+		"F": json.Number(""),
+	})
+	require.NoError(t, err)
+	expected := `A = 1.1
+B = 0.042
+C = 42
+D = 0
+E = 0.0
+F = 0
+`
+	assert.Equal(t, expected, w.String())
+}
+
 func TestEncoderOmitempty(t *testing.T) {
 	type doc struct {
 		String  string            `toml:",omitempty,multiline"`