Go : When will json.Unmarshal to struct return error?

The JSON decoder does not report an error if values in the source do not correspond to values in the target. For example, it’s not an error if the source contains the field “status”, but the target does not.

The Unmarshal function does return errors in other situations.

Syntax error

type A struct {
    Name string `json:"name"`
}
data = []byte(`{"name":what?}`)
err = json.Unmarshal(data, &a)
fmt.Println(err)  // prints character 'w' looking for beginning of value

JSON value not representable by target type:

data := []byte(`{"name":false}`)
type B struct {
  Name string `json:"name"`
}
var b B
err = json.Unmarshal(data, &b)
fmt.Println(err) // prints cannot unmarshal bool into Go value of type string

(This is one example of where the value cannot be represented by target type. There are more.)

playground example