[SR-10546] Runtime crash while iterating through collection of Decodable structs w/ URL fields

[swift-ci]

Previous ID	SR-10546
Radar	rdar://problem/50207580
Original Reporter	djs-code (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Attachment: Download

Environment

macOS 10.14.4 (18E226)

Xcode 10.2.1 (10E1001)

Swift 4.2 / 5.0

iOS Simulator 12.2

iPhone XS w/ iOS 12.0 (16A366)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, 5.0Regression, RunTimeCrash
Assignee	None
Priority	Medium

md5: 646ddc117720b95cfdf9b2a4aebb06cb

Issue Description:

When synchronizing our Core Data state with the server, we employ an O(n+m) algorithm leveraging iterators to perform the necessary insert/update/delete operations. However, as-of updating to Xcode 10.2.1, we're now seeing a consistent crash during one of these upsert operations:

* thread #5, queue = 'NSManagedObjectContext 0x10ac2d900', stop reason = EXC_BAD_ACCESS (code=1, address=0x54c0000b0)
frame #0: 0x000000019d54b6f0 libobjc.A.dylib`objc_retain + 16
frame #1: 0x00000001055112d4 libswiftCore.dylib`swift::metadataimpl::ValueWitnesses<swift::metadataimpl::ObjCRetainableBox>::initializeWithCopy(swift::OpaqueValue*, swift::OpaqueValue*, swift::TargetMetadata<swift::InProcess> const*) + 28
frame #2: 0x00000001040bebb4 StructIterationCrasher`outlined init with copy of (offset: Int, element: AppDelegate.NotificationStreamPayload.Item)? at <compiler-generated>:0

• frame Initial implementation of a @_cdecl attribute to export top-level functions to C #3: 0x00000001040bbb8c StructIterationCrasher`NotificationStreamImportOperation.main(self=0x0000000111b467c0) at NotificationStreamImportOperation.swift:86:17
  frame install Foundation via the ninja script and add the test phase for Foundation #4: 0x00000001040c0040 StructIterationCrasher`@objc NotificationStreamImportOperation.main() at <compiler-generated>:0
  frame Only run bindings-build-record on OS X due to test flakiness on Liunx… #5: 0x000000019ecdb7e8 Foundation`-[__NSOperationInternal _start:] + 748
  frame Debug Info: Don't reset the debug scope after leaving the outermost s… #6: 0x00000001040ccbe8 StructIterationCrasher`closure Redundant Load Elimination Patches #1 in closure Remove unnecessary unsafeUnwrap calls. #2 in AppDelegate.application(self=0x00000001098348a0) at AppDelegate.swift:190:32
  frame Fix a bug in SILValue's hoistAddressProjections #7: 0x00000001040cbdcc StructIterationCrasher`thunk for @escaping @callee_guaranteed () -> () at <compiler-generated>:0
  frame Simplify configure pass for Foundation to use a defined variable for XCTest's build directory #8: 0x00000001a0fead40 CoreData`developerSubmittedBlockToNSManagedObjectContextPerform + 164
  frame update related projects list to include Foundation and XCTest #9: 0x0000000104607be4 libclang_rt.asan_ios_dynamic.dylib`asan_dispatch_call_block_and_release + 316
  frame Remove the FunctionEnumeration data structure from CalleeAnalysis #10: 0x0000000105c901dc libdispatch.dylib`_dispatch_client_callout + 20
  frame Alias analysis cleanups #11: 0x0000000105c98310 libdispatch.dylib`_dispatch_lane_serial_drain + 708
  frame Add support to create xctoolchain with code sign #12: 0x0000000105c99014 libdispatch.dylib`_dispatch_lane_invoke + 420
  frame Use typed boxes to simplify capture representation in SILGen #13: 0x0000000105ca2c18 libdispatch.dylib`_dispatch_workloop_worker_thread + 1168
  frame Reduce memory footprint of the Swift compiler #14: 0x000000019df3fb38 libsystem_pthread.dylib`_pthread_wqthread + 316
  frame Remove conditional compilation of tvOS #15: 0x000000019df45dec libsystem_pthread.dylib`start_wqthread + 4

From experimenting with this, it seems that the given payload's URL field is what's triggering this, as omitting it seemingly resolves the issue.

A sample project has been attached.

[aschwaighofer]

This does not reproduce with a recent Xcode.

[swift-ci]

Comment by August S. Freytag (JIRA)

For any future investigators, I triggered this issue when adding a computed property `var ids: Set<UUID>` to a store-like class; if you'd try to iterate over the contents of the store with that property in place, you'd get a `swift::metadataimpl::ValueWitnesses` execution fault inside the `Array` iteration. Renaming the property without making any other changes resolved this, so I'm suspecting a collision of sorts under the hood.