Let CodingKey inherit CustomStringConvertible for better debugging

[inamiy]

struct MyStruct: Codable {
    let test: String
}

let json = "{}".data(using: .utf8)!

do {
    let decoder = JSONDecoder()
    let decoded = try decoder.decode(MyStruct.self, from: json)
    print(decoded)
}
catch {
    print(error)
}

Result

keyNotFound(CodableDemo.MyStruct.(CodingKeys in _CCD964A2735AA22BDC9F8350D8585760).test, Swift.DecodingError.Context(codingPath: [Optional(CodableDemo.MyStruct.(CodingKeys in _CCD964A2735AA22BDC9F8350D8585760).test)], debugDescription: "Key not found when expecting non-optional type String for coding key \"test\""))

Current DecodingError and EncodingError is hard to read when printing to the console, so I think protocol CodingKey should inherit CustomStringConvertible for better debugging.

[itaiferber]

Thanks for putting this together! If we're going to do this for debugging purposes, I think it would be helpful to conform to CustomDebugStringConvertible as well (which should definitely also display the intValue, even if it's nil).

[itaiferber]

If this has an intValue too, we should be printing that out as well.

[inamiy]

Improved description in 33582e6 and 98ed5f9, e.g. MyCodingKey(stringValue: "someKey", intValue: nil)

[itaiferber]

Please add a doc comment describing this (something like "A textual representation of this key." should suffice).

[inamiy]

Added in 33582e6.

[itaiferber]

Looks good to me! I'd just say that you can shorten the method for doing string interpolation in description, but looks good otherwise.

[itaiferber]

You can just use \(type(of: self)) instead of \(String(describing: type(of: self)))

[itaiferber]

(After you change this, BTW, I will test and merge)

[inamiy]

That's simpler! I fixed in e017508 :)

[itaiferber]

@swift-ci Please test and merge

[milseman]

@itaiferber it doesn't seem the merge took. Do you want to merge this?

[itaiferber]

@milseman Thanks for letting me know!

[inamiy]

Thanks for merge 😄

[jrose-apple]

I'm not sure it makes sense for these to be CustomStringConvertible this way. CustomDebugStringConvertible makes sense, but CustomStringConvertible is the sort of thing you'd put into an interpolation. I'd expect just the stringValue, probably.

The fact that there's not an obvious right answer might mean this should be taken to swift-evolution.

[itaiferber]

@jrose-apple This hasn't made its way to swift-4.0-branch yet, so we can tweak this and turn that off for now.