[SR-7017] JSONDecoder will decode booleans as numbers

[lilyball]

Previous ID	SR-7017
Radar	None
Original Reporter	@lilyball
Type	Bug
Status	Closed
Resolution	Done

Environment

Apple Swift version 4.0.3 (swiftlang-900.0.74.1 clang-900.0.39.2)
Target: x86_64-apple-macosx10.9

Additional Detail from JIRA

Votes	0
Component/s	Foundation
Labels	Bug
Assignee	None
Priority	Medium

md5: da644e5cdf59c1c9ee3e87e02c010d6a

Issue Description:

JSONDecoder is perfectly happy to convert a boolean to a number. This is surprising.

Example:

import Foundation

struct Foo: Decodable {
    let value: Int
}

let jsonData = "{ \"value\": true }".data(using: .utf8)!
let foo = try! JSONDecoder().decode(Foo.self, from: jsonData)
print(foo.value) // prints: 1

[spevans]

This looks to be fixed in both swift-4.1-snapshot-2018-02-13 and swift-development-snapshot-2018-02-14 as on macOS 10.12.6 w/ Xcode 9.2 your example throws:

Fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.typeMismatch(Swift.Int, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "value", intValue: nil)], debugDescription: "Expected to decode Int but found a number instead.", underlyingError: nil)): file /Users/buildnode/jenkins/workspace/oss-swift-package-osx/swift/stdlib/public/core/ErrorType.swift, line 184

using Playgrounds. However the issue does still seem to be there in Linux since it uses NSNumber and NSNumber(value: true).intValue == 1 which seems to be the problem.

[spevans]

#1442 will hopefully solve the Linux issue

[spevans]

This fix went into swift-4.1

$ cat sr-7017.swift 
import Foundation

struct Foo: Decodable {
    let value: Int
}

let jsonData = "{ \"value\": true }".data(using: .utf8)!
let foo = try! JSONDecoder().decode(Foo.self, from: jsonData)
print(foo.value) // prints: 1

$ ~/swift-4.1-RELEASE-ubuntu16.04/usr/bin/swift sr-7017.swift 
Fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.typeMismatch(Swift.Int, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "value", intValue: nil)], debugDescription: "Expected to decode Int but found a number instead.", underlyingError: nil)): file /home/buildnode/jenkins/workspace/oss-swift-4.1-package-linux-ubuntu-16_04/swift/stdlib/public/core/ErrorType.swift, line 184

$