[SR-13422] Compiler crash when evaluating Deque.first

[rnapier]

Previous ID	SR-13422
Radar	rdar://problem/67425944
Original Reporter	@rnapier
Type	Bug

Attachment: Download

Additional Detail from JIRA

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

md5: f2d290fd2d82ce48beaad4c29de73a69

Issue Description:

Using attaswift/Deque, using Collection methods sometimes confuses the compiler. Generally it just doesn't understand that Deque<T>.Element is T. Sometimes it complains that the compiler can't generate a diagnostic. And finally I got it to crash (attached).

I can't easily reproduce this in a Playground. It generally seemed to work fine. But in my project, Deque breaks the compiler any time I try to use Collection methods on it.

The crash came when I added (_buffers is a Deque<PlayBuffer>):

            let buffer = self._buffers.first

[lorentey]

@swift-ci create

[slavapestov]

I found https://github.com/attaswift/Deque/blob/master/Sources/Deque.swift, but do you mind including a test case using the library that demonstrates the crash?