URLSessionConfiguration initializer should be marked unavailable

Number:rdar://34932508 Date Originated:11-Oct-2017 09:56 AM
Status:Open Resolved:
Product:iOS + SDK Product Version:Swift 4/iOS11
Classification:Other Bug Reproducible:Always
The following code compiles with no errors:

let sessionConfig = URLSessionConfiguration.default
sessionConfig.timeoutIntervalForRequest = 10.0

But crashes at runtime with "Uncaught exception: -[NSURLSessionConfiguration setTimeoutIntervalForRequest:]: unrecognized selector sent to instance" because using the parameterless initializer is incorrect. Using `default`, `ephemeral`, or `background(withIdentifier:)` works.

Steps to Reproduce:
Compile above code in swift and run it.

Expected Results:
The parameterless initializer of URLSessionConfiguration should be marked as unavailable so that this incorrect usage does not compile

Actual Results:
Above code compiles fine, then crashes at runtime due to incorrect use

Swift 4/iOS11

I compiled using swift4 and ios11 sdks

Related to this bug filed against swift itself: https://bugs.swift.org/browse/SR-2226


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