Allow initialization from Substring etc.

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