Bundle.urls(forResourcesWithExtension:subdirectory:) returns [NSURL] on Linux instead of [URL]

[maartene]

Describe the bug
On Linux, Bundle.urls(forResourcesWithExtension:subdirectory:) returns [NSURL]? instead of [URL]?. This causes a cascade of type errors when iterating the result, because NSURL properties (path, lastPathComponent, pathExtension) are String? rather than String, and methods like deletingPathExtension() and path(percentEncoded:) from the Swift URL type are unavailable.

The singular variant Bundle.url(forResource:withExtension:) returns URL? consistently on both platforms and is unaffected.

To Reproduce
Create a new Swift package and add to main.swift:

import Foundation

let urls = Bundle.module.urls(forResourcesWithExtension: "png", subdirectory: nil) ?? []

for url in urls {
    // Linux: url is NSURL — these all fail to compile:
    let key = url.deletingPathExtension().lastPathComponent 
    let path = url.path(percentEncoded: false)
    let ext = url.pathExtension

    // ^^^ compile fine on macOS
}

Expected behavior
Independent of platform, Bundle.module.urls(forResourcesWithExtension: "png", subdirectory: nil) ?? [] returns an array of URL (Array<URL>)

Configuration (please complete the following information):

• Swift Version: Swift 6.3
• OS: latest macOS, Ubuntu 24.04

[jmschonfeld]

Transferring this to the swift-corelibs-foundation repo since that's where Bundle lives (it does not yet have a cross-platform implementation in swift-foundation)

[itingliu]

We can't change
open class func urls(forResourcesWithExtension ext: String?, subdirectory subpath: String?, in bundleURL: NSURL) -> [NSURL]?

to

open class func urls(forResourcesWithExtension ext: String?, subdirectory subpath: String?, in bundleURL: NSURL) -> [URL]?

because that's a source breaking change

The best we can do (that I can think of) is probably add another one that returns [URL] and (optionally) deprecate this [NSURL] one?

[parkera]

If it's [URL] on other platforms, I do wonder if we should consider that just a bug and change it.

[itingliu]

On Darwin it is indeed [URL]: https://developer.apple.com/documentation/foundation/bundle/urls(forresourceswithextension:subdirectory:)

We could change it and run compatibility test suites to see how breaking this would be