Swift 4.1 issue discovered around Structs with two Strings

[eweiter]

It was reported that the Swift 4.1 runtime was exhibiting a strange behavior. The behavior in question occurs when a Struct has multiple Strings and those Strings are being initialized directly from static Strings.

For instance, the following piece of code will work:

struct Output: Codable {
    let greeting: String
    let group: String
}
func main(completion: (Output?, Error?) -> Void) -> Void {
    let name = "MyName"
    let result = Output(greeting: "Hello \(name)", group: "Greetings")
    print("Log greeting:\(result.greeting)")
    completion(result, nil)
}

However the following code will not:

struct Output: Codable {
    let greeting: String
    let group: String
}
func main(completion: (Output?, Error?) -> Void) -> Void {
    let result = Output(greeting: "Hello Name", group: "bummer")
    print("Log greeting:\(result.greeting)")
    completion(result, nil)
}

It appears to be a bug within Swift itself.
We have discovered that if the code is compiled with the compiler flag to turn off optimizations then the compiling will work. This compile flag is -Xswiftc -Onone

[eweiter]

PR #3647 was merged as a temp fix until the issue is addressed in the Swift Docker image.

[eweiter]

I believe I have narrowed down the reasoning for this issue as coming from the use of the "@escaping" syntax in here https://github.com/apache/incubator-openwhisk-runtime-swift/blob/master/core/swift41Action/epilogue.swift#L98

I have stripped down this code the mainly the essentials (non-whisk related) items and when the "@escaping" option is present the code will throw a compiler error, however when I remove the statement the code will compile fine and execute successfully.

I will be opening an issue against the Swift Docker image tomorrow and will link that here when I do.

[csantanapr]

leaving open until we get a fix from swift team

[csantanapr]

Issue moved to apache/incubator-openwhisk-runtime-swift #60 via ZenHub