[SR-10078] Decode fail with an optional enum property

[swift-ci]

Previous ID	SR-10078
Radar	None
Original Reporter	thanhturin (JIRA User)
Type	Bug

Attachment: Download

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 0 | |Component/s | Compiler | |Labels | Bug, Codable | |Assignee | None | |Priority | Medium | md5: 9892ca2b5bd246ad11addcb4eddc868e

Issue Description:

Swift Codable is an awesome feature that i'm using very regularly. But while working with it I found an issue.

So I have a basic struct like this:

enum Children: String, Codable {
  case son
}

struct Parent: Codable {
  let children: Children?
}

And i tried to parse `Parent` with an undefined value from `Children`, i.e:

let rawData = """
{
  "children": "daughter"
}
""".data(using: .utf8)!

try JSONDecoder().decode(Parent.self, from: rawData)

The issue is instead of receving a Parent instance with childrean = nil, it through me a serialization error:

▿ DecodingError
  ▿ dataCorrupted : Context
    ▿ codingPath : 1 element
      - 0 : CodingKeys(stringValue: "children", intValue: nil)
    - debugDescription : "Cannot initialize Children from invalid String value daughter"
    - underlyingError : nil

Please refer to the playground file i attached below. Note that it will work if i define my own decode init function. (can just uncomment public init(from decoder: Decoder) throws

[belkadan]

This is correct behavior. It may not be correct to just produce nil here—what if it's "list of users forbidden from accessing my secret data"? Providing custom decoding behavior via init(coder:) is the right way to communicate that to the compiler.

I'm leaving this open because it's a reasonable feature request for some kind of annotation on the property to treat unknown values as nil.

[swift-ci]

Comment by Ta Phuc Thanh (JIRA)

I got it. Thanks @belkadan for your answer!