fix: correct the field priority as encoding/json when unmarshal to struct (#142)

internal/caching/fcache.go

@@ -100,11 +100,10 @@ func (self *FieldMap) Set(name string, i int) {
     s.Name = name
 
     /* add the case-insensitive version, prefer the one with smaller field ID */
-    if key := strings.ToLower(name); key != name {
+    key := strings.ToLower(name)
     if v, ok := self.m[key]; !ok || i < v {
         self.m[key] = i
     }
-    }
 }
 
 func (self *FieldMap) GetCaseInsensitive(name string) int {

issue_test/issue141_test.go

@@ -0,0 +1,105 @@
+/*
+* Copyright 2021 ByteDance Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+package issue_test
+
+import (
+    `encoding/json`
+    `testing`
+    `reflect`
+
+    `github.com/stretchr/testify/require`
+    .`github.com/bytedance/sonic`
+)
+
+type Issue141_Case_Insentive1 struct {
+    Field0 int `json:"foo"`
+    Field1 int `json:"FOO"`
+    Field2 int `json:"FoO"`
+    FOo    int
+}
+
+type Issue141_Case_Insentive2 struct {
+    Field0 int `json:"FOO"`
+    Field1 int `json:"foo"`
+    Field2 int `json:"FoO"`
+    FOo    int
+}
+
+type Issue141_Case_Insentive3 struct {
+    FOo    int
+    Field0 int `json:"FoO"`
+    Field1 int `json:"foo"`
+    Field2 int `json:"FOO"`
+}
+
+type Issue141_Case_Insentive4 struct {
+    foo    int
+    Field0 int `json:"FoO"`
+    Field1 int `json:"foo"`
+    Field2 int `json:"FOO"`
+}
+
+type  Issue141_Matched1 struct {
+    Field0 int `json:"FOO"`
+    Field1 int `json:"foo"`
+    Field2 int `json:"FoO"`
+    Foo    int
+}
+
+type  Issue141_Matched2 struct {
+    Field0 int `json:"FOO"`
+    Field1 int `json:"foo"`
+    Field2 int `json:"FoO"`
+    Foo    int
+    Field3 int `json:"Foo"`
+}
+
+// Struct field priority in unmarshal, see https://go.dev/blog/json
+func TestIssue141_StructFieldPriority(t *testing.T) {
+    data := []byte("{\"Foo\":1}")
+    for _, factory := range []func() interface{}{
+        func() interface{} { return new(Issue141_Case_Insentive1) },
+        func() interface{} { return new(Issue141_Case_Insentive2) },
+        func() interface{} { return new(Issue141_Case_Insentive3) },
+        func() interface{} { return new(Issue141_Case_Insentive4) },
+        func() interface{} { return new(Issue141_Matched1) },
+        func() interface{} { return new(Issue141_Matched2) },
+    }{
+        v1, v2 := factory(), factory()
+        err1 := json.Unmarshal(data, &v1)
+        err2 := Unmarshal(data, &v2)
+        require.NoError(t, err1)
+        require.NoError(t, err2)
+        require.Equal(t, v1, v2)
+
+        switch reflect.TypeOf(v2).Elem() {
+        case reflect.TypeOf(Issue141_Case_Insentive1{}):
+            println("Issue141_Case_Insentive1.Field0(tag foo) is ", v2.(*Issue141_Case_Insentive1).Field0)
+        case reflect.TypeOf(Issue141_Case_Insentive2{}):
+            println("Issue141_Case_Insentive2.Field0(tag FOO) is ", v2.(*Issue141_Case_Insentive2).Field0)
+        case reflect.TypeOf(Issue141_Case_Insentive3{}):
+            println("Issue141_Case_Insentive3.FOo is ", v2.(*Issue141_Case_Insentive3).FOo)
+        case reflect.TypeOf(Issue141_Case_Insentive4{}):
+            println("Issue141_Case_Insentive4.Field0(tag FoO) is ", v2.(*Issue141_Case_Insentive4).Field0)
+        case reflect.TypeOf(Issue141_Matched1{}):
+            println("Issue141_Matched1.Foo is ", v2.(*Issue141_Matched1).Foo)
+        case reflect.TypeOf(Issue141_Matched2{}):
+            println("Issue141_Matched2.Field3(tag Foo) is ", v2.(*Issue141_Matched2).Field3)
+            println("Issue141_Matched2.Foo is ", v2.(*Issue141_Matched2).Foo)
+        }
+    }
+}