Comment by Peter Wilson (JIRA)

To attempt to workaround this issue, I reversed the order in which I try to decode the object vs array of objects (the object being the common case), resulting in this updated code:

    for key in keyedContainer.allKeys {

        switch key {

        case .items:

            if let singleItem = try? keyedContainer.decode(JSRefWrapper.self, forKey: key) {

                items = \[singleItem\]

            } else if var nested = try? keyedContainer.nestedUnkeyedContainer(forKey: key) {

                items = \[\]

                while !nested.isAtEnd {

                    items!.append(try nested.decode(JSRefWrapper.self))

                }

            } else {

                throw JSError.Failure("Unable to parse items")

            }

        }

    }

    try super.init(from: decoder)

When it hits the array-of-objects case (ie, exception raised/ignored in first if test) in a unit test parsing this JSON:

            "properties": {

                "feet": {"type": "array", "items": \[ { "type": "number" } \] },

                "toes": {"type": "array", "items": { "type": "number" } },

            },

it crashes during the super.init(from🙂 call (which is the default implementation for an object) as if it is trying to parse the current object as an array, which is probably due to the same state-restoration issue.

fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.typeMismatch(Swift.Dictionary<Swift.String, Any>, Swift.DecodingError.Context(codingPath: [schemas.JSObjectSchema.ObjectCodingKeys.properties, Swift._DictionaryCodingKey(stringValue: "feet", intValue: nil), schemas.JSArraySchema.ArrayCodingKeys.items], debugDescription: "Expected to decode Dictionary<String, Any> but found an array instead.", underlyingError: nil)): file /home/buildnode/jenkins/workspace/oss-swift-4.0-package-linux-ubuntu-14_04/swift/stdlib/public/core/ErrorType.swift, line 181

Current stack trace:

0 libswiftCore.so 0x00007f71d593ce50 _swift_stdlib_reportFatalErrorInFile + 221

1 libswiftCore.so 0x00007f71d56481b0 closure #1 in closure #1 in closure #1 in assertionFailure(:_:file:line:flags🙂 + 284

2 libswiftCore.so 0x00007f71d58e6fd1 <unavailable> + 4149201

3 libswiftCore.so 0x00007f71d58fd689 <unavailable> + 4241033

4 libswiftCore.so 0x00007f71d5647a8b <unavailable> + 1399435

5 libswiftCore.so 0x00007f71d5860059 <unavailable> + 3596377

6 libswiftCore.so 0x00007f71d589de3f <unavailable> + 3849791

7 libswiftCore.so 0x00007f71d5647a8b <unavailable> + 1399435

8 libswiftCore.so 0x00007f71d57e0140 specialized assertionFailure(:_:file:line:flags🙂 + 144

9 libswiftCore.so 0x00007f71d56955d0 swift_unexpectedError + 371

10 openapi_indexerPackageTests.xctest 0x000000000051849d <unavailable> + 1148061

11 openapi_indexerPackageTests.xctest 0x0000000000505484 <unavailable> + 1070212

12 openapi_indexerPackageTests.xctest 0x0000000000504c66 <unavailable> + 1068134

13 openapi_indexerPackageTests.xctest 0x000000000050a56a <unavailable> + 1090922

14 openapi_indexerPackageTests.xctest 0x0000000000509ce4 <unavailable> + 1088740

15 openapi_indexerPackageTests.xctest 0x000000000050b41c <unavailable> + 1094684

16 libFoundation.so 0x00007f71d5148120 JSONDecoder.decode<A>(_:from🙂 + 1185

17 openapi_indexerPackageTests.xctest 0x000000000040f5f0 <unavailable> + 62960

18 openapi_indexerPackageTests.xctest 0x00000000004298b2 <unavailable> + 170162

19 openapi_indexerPackageTests.xctest 0x000000000040a056 <unavailable> + 41046

20 openapi_indexerPackageTests.xctest 0x000000000042983b <unavailable> + 170043

21 libXCTest.so 0x00007f71d5c42c7f <unavailable> + 203903

22 libXCTest.so 0x00007f71d5c40721 <unavailable> + 194337

23 libXCTest.so 0x00007f71d5c4296f <unavailable> + 203119

24 libXCTest.so 0x00007f71d5c428ab <unavailable> + 202923

25 libXCTest.so 0x00007f71d5c44119 <unavailable> + 209177

26 libXCTest.so 0x00007f71d5c435c0 <unavailable> + 206272

27 libXCTest.so 0x00007f71d5c26800 XCTestCase.invokeTest() + 102

28 libXCTest.so 0x00007f71d5c36ea6 <unavailable> + 155302

29 libXCTest.so 0x00007f71d5c26740 XCTestCase.perform(_🙂 + 14

30 libXCTest.so 0x00007f71d5c20f20 XCTest.run() + 662

31 libXCTest.so 0x00007f71d5c3777b <unavailable> + 157563

32 libXCTest.so 0x00007f71d5c376b0 <unavailable> + 157360

33 libXCTest.so 0x00007f71d5c37a84 <unavailable> + 158340

34 libXCTest.so 0x00007f71d5c233b0 XCTMain(_🙂 + 3770

35 openapi_indexerPackageTests.xctest 0x000000000040991a <unavailable> + 39194

36 libc.so.6 0x00007f71d3801e50 __libc_start_main + 245

37 openapi_indexerPackageTests.xctest 0x0000000000409049 <unavailable> + 36937

Comment by Peter Wilson (JIRA)

I tested the code with Swift 5.3.3 and it no longer generates an error. I don't see the problem code in the Foundation JSON handling code, either. Looks like it has been totally rewritten to eliminate modifying `self.codingPath` directly.