support struct tag

Author: Tao Wen

gen/main.go

@@ -210,12 +210,28 @@ func genStruct(structType *ast.StructType) {
 	_l("    switch {")
 	for _, field := range structType.Fields.List {
 		fieldName := field.Names[0].Name
+		encodedFieldName := fieldName
+		if field.Tag != nil {
+			t, _ := strconv.Unquote(field.Tag.Value)
+			tags, err := parseStructTag(t)
+			if err != nil {
+				reportError(fmt.Errorf("%s: %w", t, err))
+				return
+			}
+			jsonTag := tags["json"]
+			if jsonTag != nil && len(jsonTag) > 0 {
+				if jsonTag[0] == "-" {
+					continue
+				}
+				encodedFieldName = jsonTag[0]
+			}
+		}
 		isNotExported := unicode.IsLower(rune(fieldName[0])) || fieldName[0] == '_'
 		if isNotExported {
 			continue
 		}
 		ptr := fmt.Sprintf("&(*out).%s", fieldName)
-		_f("    case field == `%s`:", fieldName)
+		_f("    case field == `%s`:", encodedFieldName)
 		genDecodeStmt(field.Type, ptr)
 	}
 	_l("    default:")

gen/structtag.go

@@ -0,0 +1,94 @@
+package main
+
+// copied from https://github.com/fatih/structtag/blob/master/tags.go
+
+import (
+	"errors"
+	"strconv"
+	"strings"
+)
+
+var (
+	errTagSyntax      = errors.New("bad syntax for struct tag pair")
+	errTagKeySyntax   = errors.New("bad syntax for struct tag key")
+	errTagValueSyntax = errors.New("bad syntax for struct tag value")
+
+	errKeyNotSet      = errors.New("tag key does not exist")
+	errTagNotExist    = errors.New("tag does not exist")
+	errTagKeyMismatch = errors.New("mismatch between key and tag.key")
+)
+
+// parseStructTag parses a single struct field tag and returns the set of tags.
+func parseStructTag(tag string) (map[string][]string, error) {
+	tags := map[string][]string{}
+
+	hasTag := tag != ""
+
+	// NOTE(arslan) following code is from reflect and vet package with some
+	// modifications to collect all necessary information and extend it with
+	// usable methods
+	for tag != "" {
+		// Skip leading space.
+		i := 0
+		for i < len(tag) && tag[i] == ' ' {
+			i++
+		}
+		tag = tag[i:]
+		if tag == "" {
+			break
+		}
+
+		// Scan to colon. A space, a quote or a control character is a syntax
+		// error. Strictly speaking, control chars include the range [0x7f,
+		// 0x9f], not just [0x00, 0x1f], but in practice, we ignore the
+		// multi-byte control characters as it is simpler to inspect the tag's
+		// bytes than the tag's runes.
+		i = 0
+		for i < len(tag) && tag[i] > ' ' && tag[i] != ':' && tag[i] != '"' && tag[i] != 0x7f {
+			i++
+		}
+
+		if i == 0 {
+			return nil, errTagKeySyntax
+		}
+		if i+1 >= len(tag) || tag[i] != ':' {
+			return nil, errTagSyntax
+		}
+		if tag[i+1] != '"' {
+			return nil, errTagValueSyntax
+		}
+
+		key := string(tag[:i])
+		tag = tag[i+1:]
+
+		// Scan quoted string to find value.
+		i = 1
+		for i < len(tag) && tag[i] != '"' {
+			if tag[i] == '\\' {
+				i++
+			}
+			i++
+		}
+		if i >= len(tag) {
+			return nil, errTagValueSyntax
+		}
+
+		qvalue := string(tag[:i+1])
+		tag = tag[i+1:]
+
+		value, err := strconv.Unquote(qvalue)
+		if err != nil {
+			return nil, errTagValueSyntax
+		}
+
+		options := strings.Split(value, ",")
+
+		tags[key] = options
+	}
+
+	if hasTag && len(tags) == 0 {
+		return nil, nil
+	}
+
+	return tags, nil
+}

value_tests/WithStructTag.go

@@ -0,0 +1,7 @@
+package value_tests
+
+//go:generate go run github.com/json-iterator/tinygo/gen
+type WithStructTag struct {
+	Field1 string `json:"field1"`
+	Field2 string `json:"-"`
+}

value_tests/WithStructTag_json.go

@@ -0,0 +1,26 @@
+package value_tests
+
+import jsoniter "github.com/json-iterator/tinygo"
+
+func WithStructTag_json_unmarshal(iter *jsoniter.Iterator, out *WithStructTag) {
+  more := iter.ReadObjectHead()
+  for more {
+    field := iter.ReadObjectField()
+    switch {
+    case field == `field1`:
+    iter.ReadString(&(*out).Field1)
+    default:
+      iter.Skip()
+    }
+    more = iter.ReadObjectMore()
+  }
+}
+type WithStructTag_json struct {
+}
+func (json WithStructTag_json) Type() interface{} {
+  var val WithStructTag
+  return &val
+}
+func (json WithStructTag_json) Unmarshal(iter *jsoniter.Iterator, val interface{}) {
+  WithStructTag_json_unmarshal(iter, val.(*WithStructTag))
+}

value_tests/struct_test.go

@@ -17,3 +17,9 @@ func Test_struct2(t *testing.T) {
 	var val2 AnonymousStruct
 	compareWithStdlib(`{ "Value": {"Name":"hello","Price":100} }`, jsoniter.CreateJsonAdapter(AnonymousStruct_json{}), &val1, &val2)
 }
+
+func Test_struct3(t *testing.T) {
+	var val1 WithStructTag
+	var val2 WithStructTag
+	compareWithStdlib(`{ "field1": "hello", "Field2": "world" }`, jsoniter.CreateJsonAdapter(WithStructTag_json{}), &val1, &val2)
+}