encoding/json: simplify encodeState.{string, stringBytes}

As correctly mentioned in #11883, encodeState.string and
encodeState.stringBytes never return an error.
This CL removes the error from the function signatures and somewhat
simplifies call sites.

Fixes #11883

Change-Id: I1d1853d09631c545b68b5eea86ff7daa2e0ca10b
Reviewed-on: https://go-review.googlesource.com/15836
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/encoding/json/encode.go

@@ -448,12 +448,10 @@ func textMarshalerEncoder(e *encodeState, v reflect.Value, quoted bool) {
 	}
 	m := v.Interface().(encoding.TextMarshaler)
 	b, err := m.MarshalText()
-	if err == nil {
-		_, err = e.stringBytes(b)
-	}
 	if err != nil {
 		e.error(&MarshalerError{v.Type(), err})
 	}
+	e.stringBytes(b)
 }
 
 func addrTextMarshalerEncoder(e *encodeState, v reflect.Value, quoted bool) {
@@ -464,12 +462,10 @@ func addrTextMarshalerEncoder(e *encodeState, v reflect.Value, quoted bool) {
 	}
 	m := va.Interface().(encoding.TextMarshaler)
 	b, err := m.MarshalText()
-	if err == nil {
-		_, err = e.stringBytes(b)
-	}
 	if err != nil {
 		e.error(&MarshalerError{v.Type(), err})
 	}
+	e.stringBytes(b)
 }
 
 func boolEncoder(e *encodeState, v reflect.Value, quoted bool) {
@@ -783,7 +779,7 @@ func (sv stringValues) Less(i, j int) bool { return sv.get(i) < sv.get(j) }
 func (sv stringValues) get(i int) string   { return sv[i].String() }
 
 // NOTE: keep in sync with stringBytes below.
-func (e *encodeState) string(s string) (int, error) {
+func (e *encodeState) string(s string) int {
 	len0 := e.Len()
 	e.WriteByte('"')
 	start := 0
@@ -855,11 +851,11 @@ func (e *encodeState) string(s string) (int, error) {
 		e.WriteString(s[start:])
 	}
 	e.WriteByte('"')
-	return e.Len() - len0, nil
+	return e.Len() - len0
 }
 
 // NOTE: keep in sync with string above.
-func (e *encodeState) stringBytes(s []byte) (int, error) {
+func (e *encodeState) stringBytes(s []byte) int {
 	len0 := e.Len()
 	e.WriteByte('"')
 	start := 0
@@ -931,7 +927,7 @@ func (e *encodeState) stringBytes(s []byte) (int, error) {
 		e.Write(s[start:])
 	}
 	e.WriteByte('"')
-	return e.Len() - len0, nil
+	return e.Len() - len0
 }
 
 // A field represents a single field found in a struct.

src/encoding/json/encode_test.go

@@ -381,16 +381,10 @@ func TestStringBytes(t *testing.T) {
 		r = append(r, i)
 	}
 	s := string(r) + "\xff\xff\xffhello" // some invalid UTF-8 too
-	_, err := es.string(s)
-	if err != nil {
-		t.Fatal(err)
-	}
+	es.string(s)
 
 	esBytes := &encodeState{}
-	_, err = esBytes.stringBytes([]byte(s))
-	if err != nil {
-		t.Fatal(err)
-	}
+	esBytes.stringBytes([]byte(s))
 
 	enc := es.Buffer.String()
 	encBytes := esBytes.Buffer.String()