decode: Fix DecodeTypeError offsets

1 files changed, 48 insertions, 8 deletions

diff --git a/decode.go b/decode.go
index 3c51c4b..a7536f5 100644
--- a/decode.go
+++ b/decode.go
@@ -91,6 +91,7 @@ type Decoder struct {
 
 	// state
 	err         error
+	posStack    []int64
 	structStack []decodeStackItem
 }
 
@@ -150,6 +151,14 @@ func (dec *Decoder) More() bool {
 	return e == nil && t != internal.RuneTypeEOF
 }
 
+func (dec *Decoder) posStackPush() {
+	dec.posStack = append(dec.posStack, dec.InputOffset())
+}
+
+func (dec *Decoder) posStackPop() {
+	dec.posStack = dec.posStack[:len(dec.posStack)-1]
+}
+
 func (dec *Decoder) structStackPush(par reflect.Type, idx any) {
 	dec.structStack = append(dec.structStack, decodeStackItem{par, idx})
 }
@@ -266,7 +275,7 @@ func (dec *Decoder) panicType(jTyp string, gTyp reflect.Type, err error) {
 			GoType:   gTyp,
 			JSONType: jTyp,
 			Err:      err,
-			Offset:   dec.InputOffset(),
+			Offset:   dec.posStack[len(dec.posStack)-1],
 		},
 	})
 }
@@ -381,6 +390,8 @@ var kind2bits = map[reflect.Kind]int{
 }
 
 func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
+	dec.posStackPush()
+	defer dec.posStackPop()
 	typ := val.Type()
 	switch {
 	case val.CanAddr() && reflect.PointerTo(typ) == rawMessagePtrType:
@@ -388,17 +399,17 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
 		var buf bytes.Buffer
 		dec.scan(&buf)
 		if err := val.Addr().Interface().(*json.RawMessage).UnmarshalJSON(buf.Bytes()); err != nil {
-			dec.panicType(t.JSONType(), typ, err)
+			dec.panicType(t.JSONType(), reflect.PointerTo(typ), err)
 		}
 	case val.CanAddr() && reflect.PointerTo(typ).Implements(decodableType):
 		t := dec.peekRuneType()
 		obj := val.Addr().Interface().(Decodable)
 		l := dec.limitingScanner()
 		if err := obj.DecodeJSON(l); err != nil {
-			dec.panicType(t.JSONType(), typ, err)
+			dec.panicType(t.JSONType(), reflect.PointerTo(typ), err)
 		}
 		if _, _, err := l.ReadRune(); err != io.EOF {
-			dec.panicType(t.JSONType(), typ, fmt.Errorf("did not consume entire %s", t.JSONType()))
+			dec.panicType(t.JSONType(), reflect.PointerTo(typ), fmt.Errorf("did not consume entire %s", t.JSONType()))
 		}
 	case val.CanAddr() && reflect.PointerTo(typ).Implements(jsonUnmarshalerType):
 		t := dec.peekRuneType()
@@ -406,7 +417,7 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
 		dec.scan(&buf)
 		obj := val.Addr().Interface().(json.Unmarshaler)
 		if err := obj.UnmarshalJSON(buf.Bytes()); err != nil {
-			dec.panicType(t.JSONType(), typ, err)
+			dec.panicType(t.JSONType(), reflect.PointerTo(typ), err)
 		}
 	case val.CanAddr() && reflect.PointerTo(typ).Implements(textUnmarshalerType):
 		if nullOK && dec.peekRuneType() == internal.RuneTypeNullN {
@@ -530,9 +541,13 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
 			index := indexStruct(typ)
 			var nameBuf strings.Builder
 			dec.decodeObject(typ, func() {
+				dec.posStackPush()
+				defer dec.posStackPop()
 				nameBuf.Reset()
 				dec.decodeString(nil, &nameBuf)
 			}, func() {
+				dec.posStackPush()
+				defer dec.posStackPop()
 				name := nameBuf.String()
 				dec.structStackPush(typ, name)
 				defer dec.structStackPop()
@@ -613,17 +628,19 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
 					val.Set(reflect.MakeMap(typ))
 				}
 				var nameBuf bytes.Buffer
+				var nameValPtr reflect.Value
 				dec.decodeObject(typ, func() {
+					dec.posStackPush()
+					defer dec.posStackPop()
 					nameBuf.Reset()
 					dec.decodeString(nil, &nameBuf)
-				}, func() {
 					nameValTyp := typ.Key()
-					nameValPtr := reflect.New(nameValTyp)
+					nameValPtr = reflect.New(nameValTyp)
 					switch {
 					case reflect.PointerTo(nameValTyp).Implements(textUnmarshalerType):
 						obj := nameValPtr.Interface().(encoding.TextUnmarshaler)
 						if err := obj.UnmarshalText(nameBuf.Bytes()); err != nil {
-							dec.panicType("string", nameValTyp, err)
+							dec.panicType("string", reflect.PointerTo(nameValTyp), err)
 						}
 					default:
 						switch nameValTyp.Kind() {
@@ -645,6 +662,9 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
 							dec.panicType("object", typ, &DecodeArgumentError{Type: nameValTyp})
 						}
 					}
+				}, func() {
+					dec.posStackPush()
+					defer dec.posStackPop()
 					dec.structStackPush(typ, nameValPtr.Elem())
 					defer dec.structStackPop()
 
@@ -699,6 +719,8 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
 					}
 					i := 0
 					dec.decodeArray(typ, func() {
+						dec.posStackPush()
+						defer dec.posStackPop()
 						dec.structStackPush(typ, i)
 						defer dec.structStackPop()
 						mValPtr := reflect.New(typ.Elem())
@@ -718,6 +740,8 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) {
 			i := 0
 			n := val.Len()
 			dec.decodeArray(typ, func() {
+				dec.posStackPush()
+				defer dec.posStackPop()
 				dec.structStackPush(typ, i)
 				defer dec.structStackPop()
 				if i < n {
@@ -776,9 +800,13 @@ func (dec *Decoder) decodeAny() any {
 		typ := reflect.TypeOf(ret)
 		var nameBuf strings.Builder
 		dec.decodeObject(typ, func() {
+			dec.posStackPush()
+			defer dec.posStackPop()
 			nameBuf.Reset()
 			dec.decodeString(nil, &nameBuf)
 		}, func() {
+			dec.posStackPush()
+			defer dec.posStackPop()
 			name := nameBuf.String()
 			dec.structStackPush(typ, name)
 			defer dec.structStackPop()
@@ -789,6 +817,8 @@ func (dec *Decoder) decodeAny() any {
 		ret := []any{}
 		typ := reflect.TypeOf(ret)
 		dec.decodeArray(typ, func() {
+			dec.posStackPush()
+			defer dec.posStackPop()
 			dec.structStackPush(typ, len(ret))
 			defer dec.structStackPop()
 			ret = append(ret, dec.decodeAny())
@@ -840,8 +870,12 @@ func DecodeObject(r io.RuneScanner, decodeKey, decodeVal func(io.RuneScanner) er
 		}
 	}()
 	dec := NewDecoder(r)
+	dec.posStackPush()
+	defer dec.posStackPop()
 	dec.decodeObject(nil,
 		func() {
+			dec.posStackPush()
+			defer dec.posStackPop()
 			l := dec.limitingScanner()
 			if err := decodeKey(l); err != nil {
 				dec.panicType("string", nil, err)
@@ -851,6 +885,8 @@ func DecodeObject(r io.RuneScanner, decodeKey, decodeVal func(io.RuneScanner) er
 			}
 		},
 		func() {
+			dec.posStackPush()
+			defer dec.posStackPop()
 			t := dec.peekRuneType()
 			l := dec.limitingScanner()
 			if err := decodeVal(l); err != nil {
@@ -910,7 +946,11 @@ func DecodeArray(r io.RuneScanner, decodeMember func(r io.RuneScanner) error) (e
 		}
 	}()
 	dec := NewDecoder(r)
+	dec.posStackPush()
+	defer dec.posStackPop()
 	dec.decodeArray(nil, func() {
+		dec.posStackPush()
+		defer dec.posStackPop()
 		t := dec.peekRuneType()
 		l := dec.limitingScanner()
 		if err := decodeMember(l); err != nil {