[SR-4732] "Tree" enum crashes at runtime "cyclic metadata dependency detected, aborting" #47309
Description
| Previous ID | SR-4732 |
| Radar | None |
| Original Reporter | mattgallagher (JIRA User) |
| Type | Bug |
| Status | Resolved |
| Resolution | Duplicate |
Environment
Mac Pro 5,1, macOS Sierra 10.12.4
Tested both Xcode 8.3.2 and swift-DEVELOPMENT-SNAPSHOT-2017-04-24-a-osx
Additional Detail from JIRA
| Votes | 0 |
| Component/s | |
| Labels | Bug, RunTimeCrash, Runtime |
| Assignee | None |
| Priority | Medium |
md5: ff2afb9391fe46a532bd849ab2c2aca2
duplicates:
- SR-263 Implement a general solution to prevent deadlocks when generic types rely on their own metadata recursively
relates to:
- SR-5086 Cyclic metadata dependency error in generic type with nested enum with associated value of outer generic type
Issue Description:
In Xcode 8.3.2 and the latest development snapshot (April 24, 2017), the following code:
enum Tree<Node> {
case parentAndChildren(Node, Array<Tree<Node>>)
case leaf(Node)
}
let a = Tree<String>.parentAndChildren("parent", [Tree<String>.leaf("leaf")])
print(a)crashes at runtime on the `let a = Tree` line with the error:
> GenericCache(0x100658d08): cyclic metadata dependency detected, aborting
By my understanding, this should be valid code, despite the recursive definition, since the layout of `Array` does not depend on its generic parameter.
Indeed, change the definition of `parentAndChildren` to:
case parentWithChildren(Array<Tree<Node>>)and there's no problem – the code works as expected.
In addition to changing the contents of the `case`, it is possible to declare the original `parentAndChildren` case as `indirect` and the problem goes away.
Ideally, the original code should work. If that isn't possible, a compile time error (forcing the use of `indirect`) would be preferable to a runtime crash.
Previous bugs returning the same error include:
However, it's not clear if either of these are precisely the same problem.