Fix url appending(queryItems:) method to prevent it from adding empty queryItems

[EngOmarElsayed]

Prevent appending ? to URL when query items array is empty

Motivation:

When calling URL.appending(queryItems:) with an empty array, the current implementation appends a trailing ? to the URL (e.g., "www.google.com" becomes "www.google.com?"). This produces potentially invalid URLs and forces users to add defensive checks before calling the method.

Related to this issue #1548

Modifications:

Added an early return guard in appending(queryItems:) that returns self unchanged when the provided queryItems array is empty.

Result:

Calling url.appending(queryItems: []) now returns the original URL without any modifications, allowing developers to chain URL construction methods without defensive empty-array checks:

// Before: "www.google.com?"
// After:  "www.google.com"
let url = URL(string: "www.google.com")!.appending(queryItems: [])

Testing:

• Added a test case verifying that appending an empty query items array returns the original URL unchanged
• Verified existing tests pass to ensure no regression in behavior when non-empty query items are provided

[jrflat]

Thanks for opening this PR up for discussion! I think there's some app compatibility risk with this change we'll need to consider. For instance, an app might assume that a URL they append query items to will always have a query:

url.append(queryItems: queryItems)
print(url.query!) // Crash

It's a bit of a contrived example, but unexpectedly nil properties can often lead to compatibility issues. (It might also trigger different code paths for an if let query = ... block, for example.) Another argument against changing the current behavior is that other URL and URLComponents methods behave similarly, e.g:

var comp = URLComponents(string: "/path")!
comp.queryItems = []
print(comp) // "/path?" -- appends "?"

let url = URL(string: "/path")!
print(url.appending(path: "")) // "/path/" -- appends "/"
print(url.appendingPathComponent("")) // "/path/" -- appends "/"

let hostURL = URL(string: "https://example.com")!
print(hostURL.appending(path: "")) // "https://example.com/" -- appends "/"

I'll admit that URLComponents.queryItems isn't exactly the same as URL.appending(queryItems:) since you can set comp.queryItems = nil to remove the query and "?" entirely, but it's pretty similar.

Overall, I would lean towards keeping the current behavior, but I'm happy to hear a counterargument! :)

[EngOmarElsayed]

Replied in the issue page: #1548

[EngOmarElsayed]

Better solution to prevent any compatibility risk #1650 @jrflat