EXC_BREAKPOINT crash when using ReplaceError parser

[russellyeo]

I have encountered a crash when using replaceError(with:), and can reproduce it using the example documented in the OneOf parser.

enum Currency { case eur, gbp, usd, unknown }

let currency = OneOf {
    "€".map { Currency.eur }
    "£".map { Currency.gbp }
    "$".map { Currency.usd }
}
.replaceError(with: Currency.unknown)

print(currency.parse("$")) // Currency.usd
print(currency.parse("฿")) // Thread 1: EXC_BREAKPOINT (code=1, subcode=0x100004650)

Using a SPM executable package on Xcode 15.0.1 (15A507)

I tried stepping through the library code to try see if I could find the root cause, but I think it is beyond my ability/understanding!

Thanks,
Russell

[griffrawk]

Xcode 16.1 and swift-parsing 0.13.0

Also receiving the same error in the same example. I was testing using the example because I was getting something strange in my own code where .replaceError appeared to do nothing. I thought if the example was Ok, then it was something I'm doing wrong, but now I'm not sure...

func oneOfExample() {
    enum Currency { case eur, gbp, usd, unknown }

    let currency = OneOf {
      "€".map { Currency.eur }
      "£".map { Currency.gbp }
      "$".map { Currency.usd }
    }
    .replaceError(with: Currency.unknown)

    print(currency.parse("$"))  // Currency.usd
    print(currency.parse("฿"))  // Currency.unknown Thread 1: EXC_BREAKPOINT (code=1, subcode=0x103370d74)
}

[mbrandonw]

Hi @griffrawk & @russellyeo, this unfortunately seems to be a Swift compiler bug in @rethrows. That is a mechanism to allow one to have throwing requirements in protocols such that if a conformance does not actually throw then you don't need try. That is why you don't have to try the .parse even though typically parsing is a failable operation.

This may be reason enough to remove @rethrows from the library, which we can do someday (or if someone wants to PR it!), but in the meantime you could also just copy-paste ReplaceError into your own project and add a throws to the parse. That alone will fix the issue.