Oh, crud, I added code in the Feedback Assistant report (FB16336663) I sent, but forgot to put it here: func relativeURLString(for urlString: String) -> String? { guard var components = URLComponents(string: urlString) else { return nil } /////// /// The order of these seems to be important on iOS 18. /// port needs to be nil-ed first or the relative URL returned ends up malformed components.port = nil components.host = nil components.scheme = nil components.port = nil /////// return components.string } func testRelativeURLStringWithPort() { let mapping = ModuleMapping(importMap: [:]) let relativeURL = mapping.relativeURLString(for: "https://aHost.com:7443/path/to/module?a=1#blah") let expected = "/path/to/module?a=1#blah" XCTAssertEqual(relativeURL, expected) }

Even returning components.url?.absoluteString in 18.x gives "///some/path"