Symlink funcs & support NSURL file-refs

* Also removes most `NSString` usage
* Also does more thorough testing in some places
* Also adds
* Fixes `Path?(_:)` resolving symlinks in some cases

README.md

@@ -178,6 +178,11 @@ check the POSIX permissions of the file first, before returning the result of
 `isExecutableFile`. `Path.swift` has done the leg-work for you so you can get on
 with your work without worries.
 
+There is also some magic going on in Foundation’s filesystem APIs, which we look
+for and ensure our API is deterministic, eg. [this test].
+
+[this test]: TODO
+
 # `Path.swift` is properly cross-platform
 
 `FileManager` on Linux is full of holes. We have found the holes and worked
@@ -199,6 +204,10 @@ Path.home/"b/c"    // => /Users/mxcl/b/c
 // joining with absolute paths omits prefixed slash
 Path.home/"/b"     // => /Users/mxcl/b
 
+// joining with .. or . works as expected
+Path.home.foo.bar.join("..")  // => /Users/mxcl/foo
+Path.home.foo.bar.join(".")   // => /Users/mxcl/foo/bar
+
 // of course, feel free to join variables:
 let b = "b"
 let c = "c"
@@ -211,8 +220,24 @@ Path.root/"~/b"    // => /~/b
 // but is here
 Path("~/foo")!     // => /Users/mxcl/foo
 
-// this does not work though
+// this works provided the user `Guest` exists
+Path("~Guest")     // => /Users/Guest
+
+// but if the user does not exist
 Path("~foo")       // => nil
+
+// paths with .. or . are resolved
+Path("/foo/bar/../baz")  // => /foo/baz
+
+// symlinks are not resolved
+Path.root.bar.symlink(as: "foo")
+Path("foo")        // => /foo
+Path.foo           // => /foo
+
+// unless you do it explicitly
+try Path.foo.readlink()  // => /bar
+                         // `readlink` only resolves the *final* path component,
+                         // thus use `realpath` if there are multiple symlinks
 ```
 
 *Path.swift* has the general policy that if the desired end result preexists,
@@ -220,30 +245,71 @@ then it’s a noop:
 
 * If you try to delete a file, but the file doesn't exist, we do nothing.
 * If you try to make a directory and it already exists, we do nothing.
+* If you call `readlink` on a non-symlink, we return `self`
 
 However notably if you try to copy or move a file with specifying `overwrite`
 and the file already exists at the destination and is identical, we don’t check
 for that as the check was deemed too expensive to be worthwhile.
 
+## Symbolic links
+
+* Two paths may represent the same *resolved* path yet not be equal due to
+    symlinks in such cases you should use `realpath` on both first if an
+    equality check is required.
+* There are several symlink paths on Mac that are typically automatically
+    resolved by Foundation, eg. `/private`, we attempt to do the same for
+    functions that you would expect it (notably `realpath`), but we do *not* for
+    `Path.init`, *nor* if you are joining a path that ends up being one of these
+    paths, (eg. `Path.root.join("var/private')`).
+
+## We do not provide change directory functionality
+
+Changing directory is dangerous, you should *always* try to avoid it and thus
+we don’t even provide the method. If you are executing a sub-process then
+use `Process.currentDirectoryURL`.
+
+If you must then use `FileManager.changeCurrentDirectory`.
+
+# I thought I should only use `URL`s?
+
+Apple recommend this because they provide a magic translation for
+[file-references embodied by URLs][file-refs], which gives you URLs like so:
+
+    file:///.file/id=6571367.15106761
+
+Therefore, if you are not using this feature you are fine. If you have URLs the correct
+way to get a `Path` is:
+
+```swift
+if let path = Path(url) {
+    /*…*/
+}
+```
+
+Our initializer calls `path` on the URL which resolves any reference to an
+actual filesystem path, however we also check the URL has a `file` scheme first.
+
+[file-refs]: https://developer.apple.com/documentation/foundation/nsurl/1408631-filereferenceurl
+
 # Installation
 
 SwiftPM:
 
 ```swift
-package.append(.package(url: "https://github.com/mxcl/Path.swift.git", from: "0.5.0"))
+package.append(.package(url: "https://github.com/mxcl/Path.swift.git", from: "0.13.0"))
 ```
 
 CocoaPods:
 
 ```ruby
-pod 'Path.swift', '~> 0.5'
+pod 'Path.swift', '~> 0.13'
 ```
 
 Carthage:
 
 > Waiting on: [@Carthage#1945](https://github.com/Carthage/Carthage/pull/1945).
 
-## Please note
+## Pre‐1.0 status
 
 We are pre 1.0, thus we can change the API as we like, and we will (to the
 pursuit of getting it *right*)! We will tag 1.0 as soon as possible.

Sources/Path+FileManager.swift

@@ -211,6 +211,32 @@ public extension Path {
         try FileManager.default.moveItem(atPath: string, toPath: newpath.string)
         return newpath
     }
+
+    /**
+     Creates a symlink of this file at `as`.
+     - Note: If `self` does not exist, is **not** an error.
+     */
+    @discardableResult
+    func symlink(as: Path) throws -> Path {
+        try FileManager.default.createSymbolicLink(atPath: `as`.string, withDestinationPath: string)
+        return `as`
+    }
+
+    /**
+     Creates a symlink of this file with the same filename in the `into` directory.
+     - Note: If into does not exist, creates the directory with intermediate directories if necessary.
+     */
+    @discardableResult
+    func symlink(into dir: Path) throws -> Path {
+        if !dir.exists {
+            try dir.mkdir(.p)
+        } else if !dir.isDirectory {
+            throw CocoaError.error(.fileWriteFileExists)
+        }
+        let dst = dir/basename()
+        try FileManager.default.createSymbolicLink(atPath: dst.string, withDestinationPath: string)
+        return dst
+    }
 }
 
 /// Options for `Path.mkdir(_:)`

Sources/Path+StringConvertibles.swift

@@ -1,5 +1,3 @@
-import class Foundation.NSString
-
 extension Path: CustomStringConvertible {    
     /// Returns `Path.string`
     public var description: String {

Sources/Path->Bool.swift

@@ -2,7 +2,7 @@ import Foundation
 #if os(Linux)
 import func Glibc.access
 #else
-import func Darwin.access
+import Darwin
 #endif
 
 public extension Path {
@@ -55,4 +55,11 @@ public extension Path {
             return false
         }
     }
+
+    /// Returns `true` if the file is a symbolic-link (symlink).
+    var isSymlink: Bool {
+        var sbuf = stat()
+        lstat(string, &sbuf)
+        return (sbuf.st_mode & S_IFMT) == S_IFLNK 
+    }
 }

Sources/Path.swift

@@ -1,4 +1,11 @@
 import Foundation
+#if !os(Linux)
+import func Darwin.realpath
+let _realpath = Darwin.realpath
+#else
+import func Glibc.realpath
+let _realpath = Glibc.realpath
+#endif
 
 /**
  A `Path` represents an absolute path on a filesystem.
@@ -32,19 +39,85 @@ import Foundation
 public struct Path: Equatable, Hashable, Comparable {
 
     init(string: String) {
+        assert(string.first == "/")
+        assert(string.last != "/" || string == "/")
+        assert(string.split(separator: "/").contains("..") == false)
         self.string = string
     }
 
-    /// Returns `nil` unless fed an absolute path.
+    /**
+     Creates a new absolute, standardized path.
+     - Note: Resolves any .. or . components.
+     - Note: Removes multiple subsequent and trailing occurences of `/`.
+     - Note: Does *not* resolve any symlinks.
+     - Note: On macOS, removes an initial component of “/private/var/automount”, “/var/automount”, or “/private” from the path, if the result still indicates an existing file or directory (checked by consulting the file system).
+     - Returns: The path or `nil` if fed a relative path or a `~foo` string where there is no user `foo`.
+     */
     public init?(_ description: String) {
-        guard description.starts(with: "/") || description.starts(with: "~/") else { return nil }
-        self.init(string: (description as NSString).standardizingPath)
+        var pathComponents = description.split(separator: "/")
+        switch description.first {
+        case "/":
+            break
+        case "~":
+            if description == "~" {
+                self = Path.home
+                return
+            }
+            let tilded: String
+            if description.hasPrefix("~/") {
+                tilded = Path.home.string
+            } else {
+                let username = String(pathComponents[0].dropFirst())
+
+                if #available(OSX 10.12, *) {
+                    guard let url = FileManager.default.homeDirectory(forUser: username) else { return nil }
+                    assert(url.scheme == "file")
+                    tilded = url.path
+                } else {
+                    guard let dir = NSHomeDirectoryForUser(username) else { return nil }
+                    tilded = dir
+                }
+            }
+            pathComponents.remove(at: 0)
+            pathComponents.insert(contentsOf: tilded.split(separator: "/"), at: 0)
+        default:
+            return nil
+        }
+
+    #if os(macOS)
+        func ifExists(withPrefix prefix: String, removeFirst n: Int) {
+            assert(prefix.split(separator: "/").count == n)
+
+            if description.hasPrefix(prefix), FileManager.default.fileExists(atPath: description) {
+                pathComponents.removeFirst(n)
+            }
+        }
+
+        ifExists(withPrefix: "/private/var/automount", removeFirst: 3)
+        ifExists(withPrefix: "/var/automount", removeFirst: 2)
+        ifExists(withPrefix: "/private", removeFirst: 1)
+    #endif
+
+        self.string = join_(prefix: "/", pathComponents: pathComponents)
+    }
+
+    public init?(_ url: URL) {
+        guard url.scheme == "file" else { return nil }
+        self.init(string: url.path)
+        //NOTE: URL cannot be a file-reference url, unlike NSURL, so this always works
+    }
+
+    public init?(_ url: NSURL) {
+        guard url.scheme == "file", let path = url.path else { return nil }
+        self.init(string: path)
+        // ^^ works even if the url is a file-reference url
     }
 
     /// :nodoc:
-    public subscript(dynamicMember pathComponent: String) -> Path {
-        let str = (string as NSString).appendingPathComponent(pathComponent)
-        return Path(string: str)
+    public subscript(dynamicMember addendum: String) -> Path {
+        //NOTE it’s possible for the string to be anything if we are invoked via
+        // explicit subscript thus we use our fully sanitized `join` function
+        return Path(string: join_(prefix: string, appending: addendum))
     }
 
 //MARK: Properties
@@ -57,6 +130,21 @@ public struct Path: Equatable, Hashable, Comparable {
         return URL(fileURLWithPath: string)
     }
 
+    /**
+     Returns a file-reference URL.
+     - Note: Only NSURL can be a file-reference-URL, hence we return NSURL.
+     - SeeAlso: https://developer.apple.com/documentation/foundation/nsurl/1408631-filereferenceurl
+     - Important: On Linux returns an file scheme NSURL for this path string.
+     */
+    public var fileReferenceURL: NSURL? {
+    #if !os(Linux)
+        // https://bugs.swift.org/browse/SR-2728
+        return (url as NSURL).perform(#selector(NSURL.fileReferenceURL))?.takeUnretainedValue() as? NSURL
+    #else
+        return NSURL(fileURLWithPath: string)
+    #endif
+    }
+
     /**
      Returns the parent directory for this path.
 
@@ -66,20 +154,37 @@ public struct Path: Equatable, Hashable, Comparable {
      - Note: always returns a valid path, `Path.root.parent` *is* `Path.root`.
      */
     public var parent: Path {
-        return Path(string: (string as NSString).deletingLastPathComponent)
+        let index = string.lastIndex(of: "/")!
+        let substr = string[string.indices.startIndex..<index]
+        return Path(string: String(substr))
     }
 
     /**
      Returns the filename extension of this path.
-     - Remark: Implemented via `NSString.pathExtension`.
+     - Remark: If there is no extension returns "".
+     - Remark: If the filename ends with any number of ".", returns "".
      - Note: We special case eg. `foo.tar.gz`.
      */
     @inlinable
     public var `extension`: String {
-        if string.hasSuffix(".tar.gz") {
+        //FIXME efficiency
+        switch true {
+        case string.hasSuffix(".tar.gz"):
             return "tar.gz"
+        case string.hasSuffix(".tar.bz"):
+            return "tar.bz"
+        case string.hasSuffix(".tar.bz2"):
+            return "tar.bz2"
+        case string.hasSuffix(".tar.xz"):
+            return "tar.xz"
+        default:
+            let slash = string.lastIndex(of: "/")!
+            if let dot = string.lastIndex(of: "."), slash < dot {
+                let foo = string.index(after: dot)
+                return String(string[foo...])
             } else {
-            return (string as NSString).pathExtension
+                return ""
+            }
         }
     }
 
@@ -93,14 +198,15 @@ public struct Path: Equatable, Hashable, Comparable {
          Path.root.join("a").join("b")   // => /a/b
          Path.root.join("a").join("/b")  // => /a/b
 
+     - Note: `..` and `.` components are interpreted.
+     - Note: pathComponent *may* be multiple components.
+     - Note: symlinks are *not* resolved.
      - Parameter pathComponent: The string to join with this path.
      - Returns: A new joined path.
      - SeeAlso: `Path./(_:_:)`
      */
-    public func join<S>(_ pathComponent: S) -> Path where S: StringProtocol {
-        //TODO standardizingPath does more than we want really (eg tilde expansion)
-        let str = (string as NSString).appendingPathComponent(String(pathComponent))
-        return Path(string: (str as NSString).standardizingPath)
+    public func join<S>(_ addendum: S) -> Path where S: StringProtocol {
+        return Path(string: join_(prefix: string, appending: addendum))
     }
 
     /**
@@ -111,6 +217,9 @@ public struct Path: Equatable, Hashable, Comparable {
          Path.root/"a"/"b"   // => /a/b
          Path.root/"a"/"/b"  // => /a/b
 
+     - Note: `..` and `.` components are interpreted.
+     - Note: pathComponent *may* be multiple components.
+     - Note: symlinks are *not* resolved.
      - Parameter lhs: The base path to join with `rhs`.
      - Parameter rhs: The string to join with this `lhs`.
      - Returns: A new joined path.
@@ -168,18 +277,72 @@ public struct Path: Equatable, Hashable, Comparable {
      - Parameter dropExtension: If `true` returns the basename without its file extension.
      */
     public func basename(dropExtension: Bool = false) -> String {
-        let str = string as NSString
+        var lastPathComponent: Substring {
+            let slash = string.lastIndex(of: "/")!
+            let index = string.index(after: slash)
+            return string[index...]
+        }
+        var go: Substring {
             if !dropExtension {
-            return str.lastPathComponent
+                return lastPathComponent
             } else {
-            let ext = str.pathExtension
+                let ext = self.extension
                 if !ext.isEmpty {
-                return String(str.lastPathComponent.dropLast(ext.count + 1))
+                    return lastPathComponent.dropLast(ext.count + 1)
                 } else {
-                return str.lastPathComponent
+                    return lastPathComponent
                 }
             }
         }
+        return String(go)
+    }
+
+    /**
+     If the path represents an actual entry that is a symlink, returns the symlink’s
+     absolute destination.
+
+     - Important: This is not exhaustive, the resulting path may still contain
+     symlink.
+     - Important: The path will only be different if the last path component is a
+     symlink, any symlinks in prior components are not resolved.
+     - Note: If file exists but isn’t a symlink, returns `self`.
+     - Note: If symlink destination does not exist, is **not** an error.
+     */
+    public func readlink() throws -> Path {
+        do {
+            let rv = try FileManager.default.destinationOfSymbolicLink(atPath: string)
+            return Path(rv) ?? parent/rv
+        } catch CocoaError.fileReadUnknown {
+            // file is not symlink, return `self`
+            assert(exists)
+            return self
+        } catch {
+        #if os(Linux)
+            // ugh: Swift on Linux
+            let nsError = error as NSError
+            if nsError.domain == NSCocoaErrorDomain, nsError.code == CocoaError.fileReadUnknown.rawValue, exists {
+                return self
+            }
+        #endif
+            throw error
+        }
+    }
+
+    /// Recursively resolves symlinks in this path.
+    public func realpath() throws -> Path {
+        guard let rv = _realpath(string, nil) else { throw CocoaError.error(.fileNoSuchFile) }
+        defer { free(rv) }
+        guard let rvv = String(validatingUTF8: rv) else { throw CocoaError.error(.fileReadUnknownStringEncoding) }
+
+        // “Removing an initial component of “/private/var/automount”, “/var/automount”,
+        // or “/private” from the path, if the result still indicates an existing file or
+        // directory (checked by consulting the file system).”
+        // ^^ we do this to not conflict with the results that other Apple APIs give
+        // which is necessary if we are to have equality checks work reliably
+        let rvvv = (rvv as NSString).standardizingPath
+
+        return Path(string: rvvv)
+    }
 
     /// Returns the locale-aware sort order for the two paths.
     /// :nodoc:
@@ -188,3 +351,38 @@ public struct Path: Equatable, Hashable, Comparable {
         return lhs.string.compare(rhs.string, locale: .current) == .orderedAscending
     }
 }
+
+@inline(__always)
+private func join_<S>(prefix: String, appending: S) -> String where S: StringProtocol {
+    return join_(prefix: prefix, pathComponents: appending.split(separator: "/"))
+}
+
+private func join_<S>(prefix: String, pathComponents: S) -> String where S: Sequence, S.Element: StringProtocol {
+    assert(prefix.first == "/")
+
+    var rv = prefix
+    for component in pathComponents {
+
+        assert(!component.contains("/"))
+
+        switch component {
+        case "..":
+            let start = rv.indices.startIndex
+            let index = rv.lastIndex(of: "/")!
+            if start == index {
+                rv = "/"
+            } else {
+                rv = String(rv[start..<index])
+            }
+        case ".":
+            break
+        default:
+            if rv == "/" {
+                rv = "/\(component)"
+            } else {
+                rv = "\(rv)/\(component)"
+            }
+        }
+    }
+    return rv
+}

Tests/PathTests/PathTests.swift

@@ -9,6 +9,10 @@ class PathTests: XCTestCase {
         XCTAssertEqual((Path.root/"///bar").string, "/bar")
         XCTAssertEqual((Path.root/"foo///bar////").string, "/foo/bar")
         XCTAssertEqual((Path.root/"foo"/"/bar").string, "/foo/bar")
+
+        XCTAssertEqual(Path.root.foo.bar.join(".."), Path.root.foo)
+        XCTAssertEqual(Path.root.foo.bar.join("."), Path.root.foo.bar)
+        XCTAssertEqual(Path.root.foo.bar.join("../baz"), Path.root.foo.baz)
     }
 
     func testEnumeration() throws {
@@ -76,15 +80,19 @@ class PathTests: XCTestCase {
     }
 
     func testExtension() {
-        XCTAssertEqual(Path.root.join("a.swift").extension, "swift")
-        XCTAssertEqual(Path.root.join("a").extension, "")
-        XCTAssertEqual(Path.root.join("a.").extension, "")
-        XCTAssertEqual(Path.root.join("a..").extension, "")
-        XCTAssertEqual(Path.root.join("a..swift").extension, "swift")
-        XCTAssertEqual(Path.root.join("a..swift.").extension, "")
-        XCTAssertEqual(Path.root.join("a.tar.gz").extension, "tar.gz")
-        XCTAssertEqual(Path.root.join("a..tar.gz").extension, "tar.gz")
-        XCTAssertEqual(Path.root.join("a..tar..gz").extension, "gz")
+        for prefix in [Path.root, Path.root.foo, Path.root.foo.bar] {
+            XCTAssertEqual(prefix.join("a.swift").extension, "swift")
+            XCTAssertEqual(prefix.join("a").extension, "")
+            XCTAssertEqual(prefix.join("a.").extension, "")
+            XCTAssertEqual(prefix.join("a..").extension, "")
+            XCTAssertEqual(prefix.join("a..swift").extension, "swift")
+            XCTAssertEqual(prefix.join("a..swift.").extension, "")
+            XCTAssertEqual(prefix.join("a.tar.gz").extension, "tar.gz")
+            XCTAssertEqual(prefix.join("a.tar.bz2").extension, "tar.bz2")
+            XCTAssertEqual(prefix.join("a.tar.xz").extension, "tar.xz")
+            XCTAssertEqual(prefix.join("a..tar.bz").extension, "tar.bz")
+            XCTAssertEqual(prefix.join("a..tar..xz").extension, "xz")
+        }
     }
 
     func testMktemp() throws {
@@ -107,28 +115,32 @@ class PathTests: XCTestCase {
     }
 
     func testBasename() {
-        XCTAssertEqual(Path.root.join("foo.bar").basename(dropExtension: true), "foo")
-        XCTAssertEqual(Path.root.join("foo").basename(dropExtension: true), "foo")
-        XCTAssertEqual(Path.root.join("foo.").basename(dropExtension: true), "foo.")
-        XCTAssertEqual(Path.root.join("foo.bar.baz").basename(dropExtension: true), "foo.bar")
+        for prefix in [Path.root, Path.root.foo, Path.root.foo.bar] {
+            XCTAssertEqual(prefix.join("foo.bar").basename(dropExtension: true), "foo")
+            XCTAssertEqual(prefix.join("foo").basename(dropExtension: true), "foo")
+            XCTAssertEqual(prefix.join("foo.").basename(dropExtension: true), "foo.")
+            XCTAssertEqual(prefix.join("foo.bar.baz").basename(dropExtension: true), "foo.bar")
+        }
     }
 
     func testCodable() throws {
-        let input = [Path.root/"bar"]
+        let input = [Path.root.foo, Path.root.foo.bar, Path.root]
         XCTAssertEqual(try JSONDecoder().decode([Path].self, from: try JSONEncoder().encode(input)), input)
     }
 
     func testRelativePathCodable() throws {
-        let root = Path.root/"bar"
+        let root = Path.root.foo
         let input = [
-            root/"foo"
+            Path.root,
+            root,
+            root.bar
         ]
 
         let encoder = JSONEncoder()
         encoder.userInfo[.relativePath] = root
         let data = try encoder.encode(input)
 
-        XCTAssertEqual(try JSONSerialization.jsonObject(with: data) as? [String], ["foo"])
+        XCTAssertEqual(try JSONSerialization.jsonObject(with: data) as? [String], ["..", "", "bar"])
 
         let decoder = JSONDecoder()
         XCTAssertThrowsError(try decoder.decode([Path].self, from: data))
@@ -148,8 +160,16 @@ class PathTests: XCTestCase {
         XCTAssertEqual(prefix/b/c, Path("/Users/mxcl/b/c"))
         XCTAssertEqual(Path.root/"~b", Path("/~b"))
         XCTAssertEqual(Path.root/"~/b", Path("/~/b"))
+
         XCTAssertEqual(Path("~/foo"), Path.home/"foo")
+        XCTAssertEqual(Path("~"), Path.home)
+        XCTAssertEqual(Path("~/"), Path.home)
+        XCTAssertEqual(Path("~///"), Path.home)
+        XCTAssertEqual(Path("/~///"), Path.root/"~")
         XCTAssertNil(Path("~foo"))
+        XCTAssertNil(Path("~foo/bar"))
+
+        XCTAssertEqual(Path("~\(NSUserName())"), Path.home)
 
         XCTAssertEqual(Path.root/"a/foo"/"../bar", Path.root/"a/bar")
         XCTAssertEqual(Path.root/"a/foo"/"/../bar", Path.root/"a/bar")
@@ -162,6 +182,9 @@ class PathTests: XCTestCase {
 
         let a = Path.home.foo
         XCTAssertEqual(a.Documents, Path.home/"foo/Documents")
+
+        // verify use of the dynamic-member-subscript works according to our rules
+        XCTAssertEqual(Path.home[dynamicMember: "../~foo"].string, "\(Path.home.parent.string)/~foo")
     }
 
     func testCopyTo() throws {
@@ -172,6 +195,14 @@ class PathTests: XCTestCase {
             XCTAssertThrowsError(try root.foo.copy(to: root.bar))
             try root.foo.copy(to: root.bar, overwrite: true)
         }
+
+        // test copy errors if directory exists at destination, even with overwrite
+        try Path.mktemp { root in
+            try root.foo.touch()
+            XCTAssert(root.foo.isFile)
+            XCTAssertThrowsError(try root.foo.copy(to: root.bar.mkdir()))
+            XCTAssertThrowsError(try root.foo.copy(to: root.bar, overwrite: true))
+        }
     }
 
     func testCopyInto() throws {
@@ -204,6 +235,14 @@ class PathTests: XCTestCase {
             XCTAssertThrowsError(try tmpdir.foo.touch().move(to: tmpdir.bar))
             try tmpdir.foo.move(to: tmpdir.bar, overwrite: true)
         }
+
+        // test move errors if directory exists at destination, even with overwrite
+        try Path.mktemp { root in
+            try root.foo.touch()
+            XCTAssert(root.foo.isFile)
+            XCTAssertThrowsError(try root.foo.move(to: root.bar.mkdir()))
+            XCTAssertThrowsError(try root.foo.move(to: root.bar, overwrite: true))
+        }
     }
 
     func testMoveInto() throws {
@@ -424,4 +463,126 @@ class PathTests: XCTestCase {
             XCTAssertThrowsError(try tmpdir.bar.touch())
         }
     }
+
+    func testSymlinkFunctions() throws {
+        try Path.mktemp { tmpdir in
+            let foo = try tmpdir.foo.touch()
+            let bar = try foo.symlink(as: tmpdir.bar)
+            XCTAssert(bar.isSymlink)
+            XCTAssertEqual(try bar.readlink(), foo)
+        }
+
+        try Path.mktemp { tmpdir in
+            let foo1 = try tmpdir.foo.touch()
+            let foo2 = try foo1.symlink(into: tmpdir.bar)
+            XCTAssert(foo2.isSymlink)
+            XCTAssert(tmpdir.bar.isDirectory)
+            XCTAssertEqual(try foo2.readlink(), foo1)
+
+            // cannot symlink into when `into` is an existing entry that is not a directory
+            let baz = try tmpdir.baz.touch()
+            XCTAssertThrowsError(try foo1.symlink(into: baz))
+        }
+
+        try Path.mktemp { tmpdir in
+            let foo = try tmpdir.foo.touch()
+            let bar = try tmpdir.bar.mkdir()
+            XCTAssertThrowsError(try foo.symlink(as: bar))
+            XCTAssert(try foo.symlink(as: bar.foo).isSymlink)
+        }
+    }
+
+    func testReadlinkOnRelativeSymlink() throws {
+        try Path.mktemp { tmpdir in
+            let foo = try tmpdir.foo.mkdir()
+            let bar = try tmpdir.bar.touch()
+
+            let task = Process()
+            task.currentDirectoryPath = foo.string
+            task.launchPath = "/bin/ln"
+            task.arguments = ["-s", "../bar", "baz"]
+            task.launch()
+            task.waitUntilExit()
+            XCTAssertEqual(task.terminationStatus, 0)
+
+            XCTAssert(tmpdir.foo.baz.isSymlink)
+
+            XCTAssertEqual(try FileManager.default.destinationOfSymbolicLink(atPath: tmpdir.foo.baz.string), "../bar")
+
+            XCTAssertEqual(try tmpdir.foo.baz.readlink(), bar)
+        }
+    }
+
+    func testReadlinkOnFileReturnsSelf() throws {
+        try Path.mktemp { tmpdir in
+            XCTAssertEqual(try tmpdir.foo.touch(), tmpdir.foo)
+            XCTAssertEqual(try tmpdir.foo.readlink(), tmpdir.foo)
+        }
+    }
+
+    func testReadlinkOnNonExistantFileThrows() throws {
+        try Path.mktemp { tmpdir in
+            XCTAssertThrowsError(try tmpdir.bar.readlink())
+        }
+    }
+
+    func testReadlinkWhereLinkDestinationDoesNotExist() throws {
+        try Path.mktemp { tmpdir in
+            let bar = try tmpdir.foo.symlink(as: tmpdir.bar)
+            XCTAssertEqual(try bar.readlink(), tmpdir.foo)
+        }
+    }
+
+    func testNoUndesiredSymlinkResolution() throws {
+
+        // this test because NSString.standardizingPath will resolve symlinks
+        // if the path you give it contains .. and the result is an actual entry
+
+        try Path.mktemp { tmpdir in
+            let foo = try tmpdir.foo.mkdir()
+            try foo.bar.mkdir().fuz.touch()
+            let baz = try foo.symlink(as: tmpdir.baz)
+            XCTAssert(baz.isSymlink)
+            XCTAssert(baz.bar.isDirectory)
+            XCTAssertEqual(baz.bar.join("..").string, "\(tmpdir)/baz")
+
+            XCTAssertEqual(Path("\(tmpdir)/baz/bar/..")?.string, "\(tmpdir)/baz")
+        }
+    }
+
+    func testRealpath() throws {
+        try Path.mktemp { tmpdir in
+            let b = try tmpdir.a.b.mkdir(.p)
+            let c = try tmpdir.a.c.touch()
+            let e = try c.symlink(as: b.e)
+            let f = try e.symlink(as: tmpdir.f)
+            XCTAssertEqual(try f.readlink(), e)
+            XCTAssertEqual(try f.realpath(), c)
+        }
+
+        try Path.mktemp { tmpdir in
+            XCTAssertThrowsError(try tmpdir.foo.realpath())
+        }
+    }
+
+    func testFileReference() throws {
+        let ref = Path.home.fileReferenceURL
+    #if !os(Linux)
+        XCTAssertTrue(ref?.isFileReferenceURL() ?? false)
+    #endif
+        XCTAssertEqual(ref?.path, Path.home.string)
+    }
+
+    func testURLInitializer() throws {
+        XCTAssertEqual(Path(Path.home.url), Path.home)
+        XCTAssertEqual(Path.home.fileReferenceURL.flatMap(Path.init), Path.home)
+        XCTAssertNil(Path(URL(string: "https://foo.com")!))
+        XCTAssertNil(Path(NSURL(string: "https://foo.com")!))
+    }
+
+    func testInitializerForRelativePath() throws {
+        XCTAssertNil(Path("foo"))
+        XCTAssertNil(Path("../foo"))
+        XCTAssertNil(Path("./foo"))
+    }
 }

Tests/PathTests/XCTestManifests.swift

@@ -17,7 +17,9 @@ extension PathTests {
         ("testExists", testExists),
         ("testExtension", testExtension),
         ("testFileHandleExtensions", testFileHandleExtensions),
+        ("testFileReference", testFileReference),
         ("testFilesystemAttributes", testFilesystemAttributes),
+        ("testInitializerForRelativePath", testInitializerForRelativePath),
         ("testIsDirectory", testIsDirectory),
         ("testJoin", testJoin),
         ("testLock", testLock),
@@ -25,6 +27,12 @@ extension PathTests {
         ("testMktemp", testMktemp),
         ("testMoveInto", testMoveInto),
         ("testMoveTo", testMoveTo),
+        ("testNoUndesiredSymlinkResolution", testNoUndesiredSymlinkResolution),
+        ("testReadlinkOnFileReturnsSelf", testReadlinkOnFileReturnsSelf),
+        ("testReadlinkOnNonExistantFileThrows", testReadlinkOnNonExistantFileThrows),
+        ("testReadlinkOnRelativeSymlink", testReadlinkOnRelativeSymlink),
+        ("testReadlinkWhereLinkDestinationDoesNotExist", testReadlinkWhereLinkDestinationDoesNotExist),
+        ("testRealpath", testRealpath),
         ("testRelativeCodable", testRelativeCodable),
         ("testRelativePathCodable", testRelativePathCodable),
         ("testRelativeTo", testRelativeTo),
@@ -32,8 +40,10 @@ extension PathTests {
         ("testSort", testSort),
         ("testStringConvertibles", testStringConvertibles),
         ("testStringExtensions", testStringExtensions),
+        ("testSymlinkFunctions", testSymlinkFunctions),
         ("testTimes", testTimes),
         ("testTouchThrowsIfCannotWrite", testTouchThrowsIfCannotWrite),
+        ("testURLInitializer", testURLInitializer),
     ]
 }