Swift URL appendingPathComponent converts `?` to `%3F`

The generic format of URL is the following:

scheme:[//[userinfo@]host[:port]]path[?query][#fragment]

The thing you have to realize is that the ? is not part of the path. It is a separator between path and query.

If you try to add ? to path, it must be URL-encoded because ? is not a valid character for a path component.

The best solution would be to drop ? from path. It has no meaning there. However, if you have a partial URL which you want to append to a base URL, then you should join them as strings:

let url = URL(string: "https://example.com")
let path = "/somePath?"
let urlWithPath = url.flatMap { URL(string: $0.absoluteString + path) }

In short, appendingPathComponent is not a function that should be used to append URL query.

You should use removingPercentEncoding on URL's absoluteString,

let url = URL(string: "https://example.com")
let path = "/somePath?"
let urlWithPath = url?.appendingPathComponent(path).absoluteString.removingPercentEncoding
print(urlWithPath!)