[SR-12670] Compiler crash with certain generic constraints

[NevinBR]

Previous ID	SR-12670
Radar	rdar://problem/62895018
Original Reporter	@NevinBR
Type	Bug
Status	Resolved
Resolution	Done

Environment

Swift 5.1.3

Xcode 11.3.1

MacOS 10.14.6

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 2f1f35b69d7ff155d7ed2e7ec91fe52c

Issue Description:

The following code crashes the compiler (specifically, swift and SourceKitService both unexpectedly quit) in Xcode 11.3.1 running Swift 5.1.3:

protocol P { associatedtype A }
enum E<A>: P {}

struct S<G: P> where G.A: Numeric {
  typealias X = G.A
  init<T>(_ x: X) where G == E<T> {}
}

func foo() { S(1) }

Note that commenting out the last line (the foo() function) will let the rest of the code compile successfully.

The initializer call S(1) seems plausibly valid since Int does conform to Numeric.

Furthermore, even if the type being initialized is fully specified as S<E<Int>>(1), it will still crash the compiler.

[dabrahams]

Crash reproduces in Swift 5.2.2 but not the 2020-04-17 release of the S4TF toolchain, which has merged apple/swift:master in the past week.

[beccadax]

@swift-ci create

[xymus]

This should be fixed in recent compilers. @NevinBR can you try with Xcode 11.5 beta 2 or a development snapshot at https://swift.org/download/#snapshots and confirm if this issue is fixed?

[swift-ci]

Comment by Daniel Sweeney (JIRA)

I just built this (the code snippet above) without a crash on the 05-04 Swift 5.3 toolchain and the 05-05 Swift Development toolchain.

It crashes the compiler and SourceKit on the Xcode 11.4.1 Toolchain though.

So it looks like this is OK in the development snapshots.

[xymus]

Thank you for everyone who confirmed this already, but I can add that the code snippet doesn't reproduce the crash in the Xcode 12 beta either.

Marking this as resolved. @NevinBR, please reopen it if you see this problem again.