(150389961) Don't add a slash when appending an empty string to an empty path and host (swiftlang#1282)

Author: jrflat

Sources/FoundationEssentials/URL/URL_Swift.swift

@@ -682,6 +682,9 @@ internal final class _SwiftURL: Sendable, Hashable, Equatable {
     }
 
     internal func appending<S: StringProtocol>(path: S, directoryHint: URL.DirectoryHint, encodingSlashes: Bool, compatibility: Bool = false) -> URL? {
+        guard !path.isEmpty || !_parseInfo.path.isEmpty || _parseInfo.netLocationRange?.isEmpty == false else {
+            return nil
+        }
         #if os(Windows)
         var pathToAppend = path.replacing(._backslash, with: ._slash)
         #else

Tests/FoundationEssentialsTests/URLTests.swift

@@ -966,8 +966,21 @@ final class URLTests : XCTestCase {
         XCTAssertEqual(example.path(), "/foo")
         XCTAssertEqual(example.absoluteString, "https://example.com/foo")
 
+        // Maintain old behavior, where appending an empty path
+        // to an empty host does not add a slash, but appending
+        // an empty path to a non-empty host does
+        example = try XCTUnwrap(URL(string: "https://example.com"))
+        example.append(path: "")
+        XCTAssertEqual(example.host(), "example.com")
+        XCTAssertEqual(example.path(), "/")
+        XCTAssertEqual(example.absoluteString, "https://example.com/")
+
         var emptyHost = try XCTUnwrap(URL(string: "scheme://"))
-        XCTAssertTrue(emptyHost.host()?.isEmpty ?? true)
+        XCTAssertNil(emptyHost.host())
+        XCTAssertTrue(emptyHost.path().isEmpty)
+
+        emptyHost.append(path: "")
+        XCTAssertNil(emptyHost.host())
         XCTAssertTrue(emptyHost.path().isEmpty)
 
         emptyHost.append(path: "foo")