URLQueryItem does not properly implement Hashable

[jbelkins]

The URLQueryItem type does not conform to the requirements of the Hashable protocol, in that equal values may have differing hashes.

To demonstrate, consider this code sample:

import Foundation

let x1 = URLQueryItem(name: "abc", value: "def")
let x2 = URLQueryItem(name: "abc", value: "def")
let x3 = URLQueryItem(name: "abc", value: "def")

if x1 == x2 && x2 == x3 && x3 == x1 {
    print("x1, x2, x3 are all equal by ==")
} else {
    print("x1, x2, x3 are not all equal by ==")
}

if x1.hashValue == x2.hashValue && x2.hashValue == x3.hashValue && x3.hashValue == x1.hashValue {
    print("x1, x2, x3 all have equal hash values")
} else {
    print("x1, x2, x3 do not all have equal hash values")
}

Run this Swift code on Mac, then on Linux, and compare outputs.

On Mac, you get:

x1, x2, x3 are all equal by ==
x1, x2, x3 all have equal hash values

This is as expected.

But on Linux, you get:

x1, x2, x3 are all equal by ==
x1, x2, x3 do not all have equal hash values

The Linux behavior is a violation of the requirements of Hashable since values that are equal by == have differing hash values.