decode: Have .peekRuneType() return a *DecodeError

1 files changed, 81 insertions, 23 deletions

diff --git a/decode.go b/decode.go
index 73d15c5..15ab766 100644
--- a/decode.go
+++ b/decode.go
@@ -289,10 +289,11 @@ func (dec *Decoder) unreadRune() {
 	}
 }
 
-func (dec *Decoder) peekRuneType() jsonparse.RuneType {
+//nolint:unparam // It will start returning errors soon.
+func (dec *Decoder) peekRuneType() (jsonparse.RuneType, *DecodeError) {
 	_, t := dec.readRune()
 	dec.unreadRune()
-	return t
+	return t, nil
 }
 
 func (dec *Decoder) expectRune(ec rune, et jsonparse.RuneType) {
@@ -396,7 +397,10 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 	typ := val.Type()
 	switch {
 	case val.CanAddr() && reflect.PointerTo(typ) == rawMessagePtrType:
-		t := dec.peekRuneType()
+		t, err := dec.peekRuneType()
+		if err != nil {
+			return err
+		}
 		var buf bytes.Buffer
 		if err := dec.scan(&buf); err != nil {
 			return err
@@ -405,7 +409,10 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 			return dec.newTypeError(t.JSONType(), reflect.PointerTo(typ), err)
 		}
 	case val.CanAddr() && reflect.PointerTo(typ).Implements(decodableType):
-		t := dec.peekRuneType()
+		t, err := dec.peekRuneType()
+		if err != nil {
+			return err
+		}
 		obj := val.Addr().Interface().(Decodable)
 		return dec.withLimitingScanner(func(l io.RuneScanner) *DecodeError {
 			if err := obj.DecodeJSON(l); err != nil {
@@ -417,7 +424,10 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 			return nil
 		})
 	case val.CanAddr() && reflect.PointerTo(typ).Implements(jsonUnmarshalerType):
-		t := dec.peekRuneType()
+		t, err := dec.peekRuneType()
+		if err != nil {
+			return err
+		}
 		var buf bytes.Buffer
 		if err := dec.scan(&buf); err != nil {
 			return err
@@ -494,7 +504,10 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 			}
 			var buf strings.Builder
 			if typ == numberType {
-				t := dec.peekRuneType()
+				t, err := dec.peekRuneType()
+				if err != nil {
+					return err
+				}
 				if err := dec.scan(&buf); err != nil {
 					return err
 				}
@@ -511,8 +524,12 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 				val.SetString(buf.String())
 			}
 		case reflect.Interface:
+			t, err := dec.peekRuneType()
+			if err != nil {
+				return err
+			}
 			if typ.NumMethod() > 0 {
-				return dec.newTypeError(dec.peekRuneType().JSONType(), typ, ErrDecodeNonEmptyInterface)
+				return dec.newTypeError(t.JSONType(), typ, ErrDecodeNonEmptyInterface)
 			}
 			// If the interface stores a pointer, try to use the type information of the pointer.
 			if !val.IsNil() && val.Elem().Kind() == reflect.Pointer {
@@ -533,11 +550,11 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 				//   in the loop) because the only way it's possible is if there's
 				//   an interface in there, which'd break from the loop on its own.
 				//
-				// ptr.CanSet() || dec.peekRuneType() != jsonparse.RuneTypeNullN
+				// ptr.CanSet() || t != jsonparse.RuneTypeNullN
 				//
 				//   We only need the pointer itself to be settable if we're
 				//   decoding null.
-				if ptr.Elem() != val && (ptr.CanSet() || dec.peekRuneType() != jsonparse.RuneTypeNullN) {
+				if ptr.Elem() != val && (ptr.CanSet() || t != jsonparse.RuneTypeNullN) {
 					if err := dec.decode(ptr, false); err != nil {
 						return err
 					}
@@ -545,7 +562,7 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 				}
 			}
 			// Couldn't get type information from a pointer; fall back to untyped mode.
-			switch dec.peekRuneType() {
+			switch t {
 			case jsonparse.RuneTypeNullN:
 				if err := dec.decodeNull(); err != nil {
 					return err
@@ -600,7 +617,11 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 								fmt.Errorf("json: cannot set embedded pointer to unexported struct: %v",
 									fVal.Type().Elem()))
 						}
-						if dec.peekRuneType() != jsonparse.RuneTypeNullN {
+						t, err := dec.peekRuneType()
+						if err != nil {
+							return err
+						}
+						if t != jsonparse.RuneTypeNullN {
 							if fVal.IsNil() {
 								fVal.Set(reflect.New(fVal.Type().Elem()))
 							}
@@ -610,7 +631,11 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 					fVal = fVal.Field(idx)
 				}
 				if field.Quote {
-					switch t := dec.peekRuneType(); t {
+					t, err := dec.peekRuneType()
+					if err != nil {
+						return err
+					}
+					switch t {
 					case jsonparse.RuneTypeNullN:
 						if err := dec.decodeNull(); err != nil {
 							return err
@@ -647,7 +672,11 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 				}
 			})
 		case reflect.Map:
-			switch t := dec.peekRuneType(); t {
+			t, err := dec.peekRuneType()
+			if err != nil {
+				return err
+			}
+			switch t {
 			case jsonparse.RuneTypeNullN:
 				if err := dec.decodeNull(); err != nil {
 					return err
@@ -713,12 +742,16 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 				return dec.newTypeError(t.JSONType(), typ, nil)
 			}
 		case reflect.Slice:
+			t, err := dec.peekRuneType()
+			if err != nil {
+				return err
+			}
 			switch {
-			case typ.Elem().Kind() == reflect.Uint8 && !(dec.peekRuneType() == jsonparse.RuneTypeArrayBeg && (false ||
+			case typ.Elem().Kind() == reflect.Uint8 && !(t == jsonparse.RuneTypeArrayBeg && (false ||
 				reflect.PointerTo(typ.Elem()).Implements(decodableType) ||
 				reflect.PointerTo(typ.Elem()).Implements(jsonUnmarshalerType) ||
 				reflect.PointerTo(typ.Elem()).Implements(textUnmarshalerType))):
-				switch t := dec.peekRuneType(); t {
+				switch t {
 				case jsonparse.RuneTypeNullN:
 					if err := dec.decodeNull(); err != nil {
 						return err
@@ -748,7 +781,7 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 					return dec.newTypeError(t.JSONType(), typ, nil)
 				}
 			default:
-				switch t := dec.peekRuneType(); t {
+				switch t {
 				case jsonparse.RuneTypeNullN:
 					if err := dec.decodeNull(); err != nil {
 						return err
@@ -810,7 +843,11 @@ func (dec *Decoder) decode(val reflect.Value, nullOK bool) (_err *DecodeError) {
 				val.Index(i).Set(reflect.Zero(typ.Elem()))
 			}
 		case reflect.Pointer:
-			switch dec.peekRuneType() {
+			t, err := dec.peekRuneType()
+			if err != nil {
+				return err
+			}
+			switch t {
 			case jsonparse.RuneTypeNullN:
 				if err := dec.decodeNull(); err != nil {
 					return err
@@ -843,7 +880,11 @@ func (dec *Decoder) scan(out fastio.RuneWriter) *DecodeError {
 }
 
 func (dec *Decoder) scanNumber(gTyp reflect.Type, out fastio.RuneWriter) *DecodeError {
-	if t := dec.peekRuneType(); !t.IsNumber() {
+	t, err := dec.peekRuneType()
+	if err != nil {
+		return err
+	}
+	if !t.IsNumber() {
 		return dec.newTypeError(t.JSONType(), gTyp, nil)
 	}
 	return dec.scan(out)
@@ -971,7 +1012,10 @@ func DecodeObject(r io.RuneScanner, decodeKey, decodeVal func(io.RuneScanner) er
 		func() *DecodeError {
 			dec.posStackPush()
 			defer dec.posStackPop()
-			t := dec.peekRuneType()
+			t, err := dec.peekRuneType()
+			if err != nil {
+				return err
+			}
 			return dec.withLimitingScanner(func(l io.RuneScanner) *DecodeError {
 				if err := decodeVal(l); err != nil {
 					// TODO: Find a better Go type to use than `nil`.
@@ -1052,7 +1096,10 @@ func DecodeArray(r io.RuneScanner, decodeMember func(r io.RuneScanner) error) (e
 	if err := dec.decodeArray(nil, func() *DecodeError {
 		dec.posStackPush()
 		defer dec.posStackPop()
-		t := dec.peekRuneType()
+		t, err := dec.peekRuneType()
+		if err != nil {
+			return err
+		}
 		return dec.withLimitingScanner(func(l io.RuneScanner) *DecodeError {
 			if err := decodeMember(l); err != nil {
 				// TODO: Find a better Go type to use than `nil`.
@@ -1144,12 +1191,20 @@ func (dec *Decoder) decodeString(gTyp reflect.Type, out fastio.RuneWriter) *Deco
 				rune(uhex[3])<<0
 		handleUnicode:
 			if utf16.IsSurrogate(c) {
-				if dec.peekRuneType() != jsonparse.RuneTypeStringEsc {
+				t, err := dec.peekRuneType()
+				if err != nil {
+					return err
+				}
+				if t != jsonparse.RuneTypeStringEsc {
 					_, _ = out.WriteRune(utf8.RuneError)
 					break
 				}
 				dec.expectRune('\\', jsonparse.RuneTypeStringEsc)
-				if dec.peekRuneType() != jsonparse.RuneTypeStringEscU {
+				t, err = dec.peekRuneType()
+				if err != nil {
+					return err
+				}
+				if t != jsonparse.RuneTypeStringEscU {
 					_, _ = out.WriteRune(utf8.RuneError)
 					break
 				}
@@ -1215,7 +1270,10 @@ func (dec *Decoder) decodeNull() *DecodeError {
 
 func (dec *Decoder) maybeDecodeNull(nullOK bool) (ok bool, err *DecodeError) {
 	if nullOK {
-		t := dec.peekRuneType()
+		t, err := dec.peekRuneType()
+		if err != nil {
+			return true, err
+		}
 		if t == jsonparse.RuneTypeNullN {
 			return true, dec.decodeNull()
 		}