[SR-10816] Changes from SE-0213 break source compatibility in Swift 4 mode

[swift-ci]

Previous ID	SR-10816
Radar	None
Original Reporter	nonsensery (JIRA User)
Type	Bug

Environment

• macOS

• Xcode 10.1 (Swift 4.2.1) and Xcode 10.2.1 (Swift 5.0.1)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, 5.0Regression
Assignee	None
Priority	Medium

md5: 1d1a6270823a72363a7fad6cc34df65c

relates to:

• SR-10259 ExpressibleByStringLiteral masks an initializer without any warning in Swift 5.

Issue Description:

Steps to reproduce

Note: This issue affects the Swift-4 mode of the Swift 5 compiler.

1. Execute the following code sample using both the Swift 4 compiler, and the Swift 5 compiler in Swift-4 compatibility mode:

struct TimeOfDay: ExpressibleByStringLiteral {
    init(_ string: String) {
        print("using init(_:)")
    }

    init(stringLiteral: String) {
        print("using init(stringLiteral:)")
    }
}

TimeOfDay.init("00:00")
TimeOfDay("00:00")

Expected result

The code should behave the same in both.

Actual result

In Swift 4, the output is:

using init(_:)
using init(_:)

In Swift-4 compatibility mode, the output is:

using init(_:)
using init(stringLiteral:)

Discussion

I understand that this change in behavior is the result of SE-0213. But, I think that change was only supposed to affect Swift 5 mode.

See this thread on the Swift forums.

[belkadan]

cc @xedin