I suppose CI will tell us, but I don't expect this will work here. I don't know the full details, but I believe that _convertErrorToNSError is effectively the implementation of as NSError, so I suspect this is likely to cause infinite recursion. To check that, I compiled

public func foo(_ e: any Error) -> NSError {
    e as NSError
}

in GodBolt on Linux and saw that it indeed compiles down to a call to this function:

output.foo(Swift.Error) -> Foundation.NSError:
        b       ($s10Foundation22_convertErrorToNSErroryAA0E0Cs0C0_pF)

That said, I don't know the answer to what this should be instead. I'd be interested to know what the type of object is here in the failing case

I did run unit tests on this locally, but it's possible we for some reason do not hit this path.

@jmschonfeld

I'd be interested to know what the type of object is here in the failing case

The original bug report has a very short reproducer:

import Foundation

public class BotError: Error {}

print(BotError().localizedDescription)

I suppose CI will tell us, but I don't expect this will work here. I don't know the full details, but I believe that _convertErrorToNSError is effectively the implementation of as NSError, so I suspect this is likely to cause infinite recursion.

If you compare

public func foo(_ e: any Error) -> NSError? {
    e as? NSError
}

public func bar(_ e: any Error) -> NSError? {
    e as NSError
}

you'll see that as? NSError causes a call to swift_dynamicCast rather than a call to _convertErrorToNSError.

Looks like with the reproducer, both error and object are the BotError instance:

(lldb) frame select 2
frame #2: 0x0000aaaae793437c TestCLI`_convertErrorToNSError(error=0x0000aaab15256780) at NSError.swift:895:16
   892 	public // COMPILER_INTRINSIC
   893 	func _convertErrorToNSError(_ error: Error) -> NSError {
   894 	    if let object = _extractDynamicValue(error as Any) {
-> 895 	        return unsafeDowncast(object, to: NSError.self)
    	               ^
   896 	    } else {
   897 	        let domain: String
   898 	        let code: Int
(lldb) frame variable
(TestCLI.BotError) error = 0x0000aaab15256780 {}
(TestCLI.BotError) object = 0x0000aaab15256780 {}

And when the error type is a struct or enum instead of a class, _extractDynamicValue returns nil