type StructA struct {
  FieldA string `form:"field_a"`
}
 
type StructB struct {
  NestedStruct StructA
  FieldB string `form:"field_b"`
}
 
type StructC struct {
  NestedStructPointer *StructA
  FieldC string `form:"field_c"`
}
 
type StructD struct {
  NestedAnonyStruct struct {
    FieldX string `form:"field_x"`
  }
  FieldD string `form:"field_d"`
}
 
func GetDataB(c *gin.Context) {
  var b StructB
  c.Bind(&b)
  c.JSON(200, gin.H{
    "a": b.NestedStruct,
    "b": b.FieldB,
  })
}
 
func GetDataC(c *gin.Context) {
  var b StructC
  c.Bind(&b)
  c.JSON(200, gin.H{
    "a": b.NestedStructPointer,
    "c": b.FieldC,
  })
}
 
func GetDataD(c *gin.Context) {
  var b StructD
  c.Bind(&b)
  c.JSON(200, gin.H{
    "x": b.NestedAnonyStruct,
    "d": b.FieldD,
  })
}
 
func main() {
  r := gin.Default()
  r.GET("/getb", GetDataB)
  r.GET("/getc", GetDataC)
  r.GET("/getd", GetDataD)
 
  r.Run()
}

$ curl "http://localhost:8080/getb"
{"a":{"FieldA":"hello"},"b":"world"}
$ curl "http://localhost:8080/getc"
{"a":{"FieldA":"hello"},"c":"world"}
$ curl "http://localhost:8080/getd"
{"d":"world","x":{"FieldX":"hello"}}

type StructX struct {
  X struct {} `form:"name_x"` // HERE have form
}
 
type StructY struct {
  Y StructX `form:"name_y"` // HERE have form
}
 
type StructZ struct {
  Z *StructZ `form:"name_z"` // HERE have form
}