json: Fix float32 encoding and add test (#1003)

This commit fixes incorrect float32 encoding. A test
case is also added.

Refs: 
* #1002
* Internal ticket: GO-860

zapcore/json_encoder.go

@@ -128,6 +128,11 @@ func (enc *jsonEncoder) AddFloat64(key string, val float64) {
 	enc.AppendFloat64(val)
 }
 
+func (enc *jsonEncoder) AddFloat32(key string, val float32) {
+	enc.addKey(key)
+	enc.AppendFloat32(val)
+}
+
 func (enc *jsonEncoder) AddInt64(key string, val int64) {
 	enc.addKey(key)
 	enc.AppendInt64(val)
@@ -297,7 +302,6 @@ func (enc *jsonEncoder) AppendUint64(val uint64) {
 }
 
 func (enc *jsonEncoder) AddComplex64(k string, v complex64) { enc.AddComplex128(k, complex128(v)) }
-func (enc *jsonEncoder) AddFloat32(k string, v float32)     { enc.AddFloat64(k, float64(v)) }
 func (enc *jsonEncoder) AddInt(k string, v int)             { enc.AddInt64(k, int64(v)) }
 func (enc *jsonEncoder) AddInt32(k string, v int32)         { enc.AddInt64(k, int64(v)) }
 func (enc *jsonEncoder) AddInt16(k string, v int16)         { enc.AddInt64(k, int64(v)) }

zapcore/json_encoder_test.go

@@ -63,6 +63,7 @@ func TestJSONEncodeEntry(t *testing.T) {
 				"M": "lob law",
 				"so": "passes",
 				"answer": 42,
+				"a_float32": 2.71,
 				"common_pie": 3.14,
 				"complex_value": "3.14-2.71i",
 				"null_value": null,
@@ -87,6 +88,7 @@ func TestJSONEncodeEntry(t *testing.T) {
 				zap.String("so", "passes"),
 				zap.Int("answer", 42),
 				zap.Float64("common_pie", 3.14),
+				zap.Float32("a_float32", 2.71),
 				zap.Complex128("complex_value", 3.14-2.71i),
 				// Cover special-cased handling of nil in AddReflect() and
 				// AppendReflect(). Note that for the latter, we explicitly test