[SR-5836] Compilation crash in Dictionary extension

[jlukas]

Previous ID	SR-5836
Radar	rdar://problem/34259886
Original Reporter	@jlukas
Type	Bug
Status	Resolved
Resolution	Done

Environment

Apple Swift version 4.0 (swiftlang-900.0.63.10 clang-900.0.36)

Additional Detail from JIRA

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

md5: b156cf3bcf7a4c66c58b83a54c3dae1b

is duplicated by:

• SR-5932 Segmentation fault: 11 when creating a Set of optionals

Issue Description:

I'm not sure what exactly is causing the crash, but I reduced it this far:

Input:

extension Dictionary {
    func doSomething<T>() -> [T:Value] {
        let pairs: [(T,Value)] = []
        return Dictionary(uniqueKeysWithValues: pairs)
    }
}

Output:

Stack dump:
0.  While emitting SIL for 'doSomething()' at /var/folders/my/75k1c85j1s5fj3myg_4x273r0000gn/T/repl1-bcce9c..swift:2:5

[belkadan]

Huh. Looks like this was working in 900.0.54.11 and then we broke it again. @rudkx, @xedin?

[rudkx]

@swift-ci create

[rudkx]

I opened a PR to add this test to our test suite: #11773

If the code is updated to return [Key : Value] rather than [T : Value] and create an array of (Key, Value) pairs rather than (T, Value) pairs, we don't crash. Apparently there was a reason to make this generic on a new type in the original code this was reduced from, though.

[slavapestov]

#12150