Allow initialization from Substring etc.

Sources/Path.swift

@@ -53,11 +53,25 @@ public struct Path: Equatable, Hashable, Comparable {
      - 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) {
+    public init?<S: StringProtocol>(_ description: S) {
         var pathComponents = description.split(separator: "/")
         switch description.first {
         case "/":
-            break
+        #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: String(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)
+
         case "~":
             if description == "~" {
                 self = Path.home
@@ -82,26 +96,11 @@ public struct Path: Equatable, Hashable, Comparable {
             #endif
             }
             pathComponents.remove(at: 0)
-            pathComponents.insert(contentsOf: tilded.split(separator: "/"), at: 0)
+            self.string = join_(prefix: tilded, pathComponents: pathComponents)
+
         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)
     }
 
     /**

Tests/PathTests/PathTests.swift

@@ -594,4 +594,14 @@ class PathTests: XCTestCase {
         XCTAssertEqual(Path.root.foo.bar.components, ["/", "foo", "bar"])
         XCTAssertEqual(Path.root.components, ["/"])
     }
+
+    func testFlatMap() throws {
+        // testing compile works
+        let foo: String? = "/a"
+        _ = foo.flatMap(Path.init)
+        let bar: Substring? = "/a"
+        _ = bar.flatMap(Path.init)
+        let baz: String.SubSequence? = "/a/b:1".split(separator: ":").first
+        _ = baz.flatMap(Path.init)
+    }
 }

Tests/PathTests/XCTestManifests.swift

@@ -1,7 +1,11 @@
+#if !canImport(ObjectiveC)
 import XCTest
 
 extension PathTests {
-    static let __allTests = [
+    // DO NOT MODIFY: This is autogenerated, use:
+    //   `swift test --generate-linuxmain`
+    // to regenerate.
+    static let __allTests__PathTests = [
         ("testBasename", testBasename),
         ("testBundleExtensions", testBundleExtensions),
         ("testCodable", testCodable),
@@ -19,6 +23,7 @@ extension PathTests {
         ("testFileHandleExtensions", testFileHandleExtensions),
         ("testFileReference", testFileReference),
         ("testFilesystemAttributes", testFilesystemAttributes),
+        ("testFlatMap", testFlatMap),
         ("testInitializerForRelativePath", testInitializerForRelativePath),
         ("testIsDirectory", testIsDirectory),
         ("testJoin", testJoin),
@@ -48,10 +53,9 @@ extension PathTests {
     ]
 }
 
-#if !os(macOS)
 public func __allTests() -> [XCTestCaseEntry] {
     return [
-        testCase(PathTests.__allTests),
+        testCase(PathTests.__allTests__PathTests),
     ]
 }
 #endif