patch,tests: logic extract and unit tests

patch/patcher.go

@@ -533,24 +533,28 @@ func (p *Patcher) patchIdent(id *ast.Ident, obj types.Object) {
 				v.Tag = &ast.BasicLit{}
 			}
 
-			//tag override
-			oldTags := strings.Split(strings.TrimSpace(strings.Trim(v.Tag.Value, "` ")), " ")
-			var newTags []string
-			for _, tag := range oldTags {
-				var key string
-				if kv := strings.Split(tag, ":"); len(kv) > 0 {
-					key = kv[0]
-				}
-				if _, exist := reflect.StructTag(tags).Lookup(key); !exist {
-					newTags = append(newTags, tag)
-				}
-			}
-			v.Tag.Value = "`" + strings.Join(append(oldTags[:len(oldTags)-1], tags), " ") + "`"
+			v.Tag.Value = "`" + mergeTags(v.Tag.Value, tags) + "`"
 			log.Printf("Add tags:\t%q.%s %s", obj.Pkg().Path(), id.Name, v.Tag.Value)
 		}
 	}
 }
 
+// Override tags
+func mergeTags(oldTag, newTag string) string {
+	oldTags := strings.Split(strings.TrimSpace(strings.Trim(oldTag, "` ")), " ")
+	var newTags []string
+	for _, tag := range oldTags {
+		var key string
+		if kv := strings.Split(tag, ":"); len(kv) > 0 {
+			key = kv[0]
+		}
+		if value, exist := reflect.StructTag(newTag).Lookup(key); !exist || value == "" {
+			newTags = append(newTags, tag)
+		}
+	}
+	return strings.Join(append(newTags, newTag), " ")
+}
+
 func (p *Patcher) patchComments(id *ast.Ident, repl string) {
 	doc, comment := p.findCommentGroups(id)
 	if doc == nil && comment == nil {

patch/patcher_test.go

@@ -0,0 +1,43 @@
+package patch
+
+import (
+	"testing"
+)
+
+func TestMergeTags(t *testing.T) {
+	tests := []struct {
+		name string
+		in   [2]string
+		want string
+	}{
+		{	name:"NotOverrideTag",
+			in: [2]string{
+				`json:"code;omitempty"`,
+				`test:"test"`,
+			},
+			want: `json:"code;omitempty" test:"test"`,
+		},
+		{  name:"OverrideSingleTag",
+			in: [2]string{
+			`json:"code;omitempty"`,
+			`json:"-" test:"test"`,
+		},
+			want: `json:"-" test:"test"`,
+		},
+		{	name:"OverrideMultiTag",
+			in: [2]string{
+			`json:"code;omitempty" test1:"test""`,
+			`test1:"test1" test2:"test2"`,
+		},
+			want: `json:"code;omitempty" test1:"test1" test2:"test2"`,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if got := mergeTags(test.in[0], test.in[1]); got != test.want {
+				t.Fatalf(" got: %s\nwant: %s\n", got, test.want)
+			}
+		})
+	}
+}