[SR-6096] Runtime-Crash when constructing KeyPath

[swift-ci]

Previous ID	SR-6096
Radar	rdar://problem/34889333
Original Reporter	tomquist (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Environment

Apple Swift version 4.0 (swiftlang-900.0.65 clang-900.0.37)
Target: x86_64-apple-macosx10.9
Xcode Version 9.0 (9A235)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, KeyPaths, RunTimeCrash
Assignee	tomquist (JIRA)
Priority	Medium

md5: 7e5bd566fa2f00a65d781a8dced48556

is duplicated by:

• SR-6110 Runtime crash with nested optional key-path
• SR-6281 Creating KeyPath with Optional Indexing Crashes
• SR-6495 Segfault when using KeyPath on final class in struct with NSObject

relates to:

• SR-6281 Creating KeyPath with Optional Indexing Crashes

Issue Description:

The following code produces a runtime crash:

protocol SomeProtocol {}
struct SomeType: SomeProtocol {}
struct Value<ValueType> {}
extension SomeProtocol {
    var asString: String? {
        return self as? String
    }
}
extension Value where ValueType: SomeProtocol {
    func doSomething() {
        print(\ValueType.asString?.endIndex)
    }
}
Value<SomeType>().doSomething()

Crash:

fatal error: UnsafeMutableRawBufferPointer with negative count
[1]    74901 illegal hardware instruction  ./test

[belkadan]

@jckarter, sound familiar?

[jckarter]

@swift-ci create

[jckarter]

#12725 should fix this.

[jckarter]

PR for 4.0 branch: #12775

[jckarter]

This should be fixed now in recent snapshots from either master or the 4.1 branch.