[stdlib] span properties for bridged String instances

Author: glessard

stdlib/public/core/StringUTF8View.swift

@@ -324,21 +324,33 @@ extension String.UTF8View {
   public var span: Span<UTF8.CodeUnit> {
     @lifetime(borrow self)
     borrowing get {
+#if _runtime(_ObjC)
+      // handle non-UTF8 Objective-C bridging cases here
+      if !_guts.isFastUTF8 && _guts._object.hasObjCBridgeableObject {
+        let storage: __StringStorage
+        if let associated = _guts.getAssociatedStorage() {
+          storage = associated
+        }
+        else {
+          storage = _guts.getOrAllocateAssociatedStorage()
+        }
+        let (start, count) = unsafe (storage.start, storage.count)
+        let span = unsafe Span(_unsafeStart: start, count: count)
+        return unsafe _overrideLifetime(span, borrowing: self)
+      }
+#endif
       let count = _guts.count
       if _guts.isSmall {
         let a = Builtin.addressOfBorrow(self)
         let address = unsafe UnsafePointer<UTF8.CodeUnit>(a)
         let span = unsafe Span(_unsafeStart: address, count: count)
         return unsafe _overrideLifetime(span, borrowing: self)
       }
-      else if _guts.isFastUTF8 {
-        let buffer = unsafe _guts._object.fastUTF8
-        _internalInvariant(count == buffer.count)
-        let span = unsafe Span(_unsafeElements: buffer)
-        return unsafe _overrideLifetime(span, borrowing: self)
-      }
-      // handle other Objective-C bridging cases here
-      fatalError("Some bridged Strings are not supported at this time")
+      _precondition(_guts.isFastUTF8)
+      let buffer = unsafe _guts._object.fastUTF8
+      _internalInvariant(count == buffer.count)
+      let span = unsafe Span(_unsafeElements: buffer)
+      return unsafe _overrideLifetime(span, borrowing: self)
     }
   }
 }

test/stdlib/Span/StringUTF8SpanProperty.swift

@@ -83,3 +83,27 @@ suite.test("Span from Large Native String's Substring")
     expectEqual(span[i], u[i])
   }
 }
+
+import Foundation
+
+let strings: [NSString: String] = [
+  "Hello, World!" as NSString: "Hello, World!",
+  "A long ASCII string exceeding 16 code units." as NSString: "A long ASCII string exceeding 16 code units.",
+  "🇯🇵" as NSString: "🇯🇵",
+  NSString(utf8String: "🏂☃❅❆❄︎⛄️❄️")!: "🏂☃❅❆❄︎⛄️❄️",
+]
+
+strings.forEach { string, expected in
+  suite.test("Span from Bridged String: \(expected)")
+  .require(.stdlib_6_2).code {
+    guard #available(SwiftStdlib 6.2, *) else { return }
+
+    let bridged = String(string)
+    let utf8 = bridged.utf8
+    let span = utf8.span
+    expectEqual(span.count, expected.utf8.count)
+    for (i,j) in zip(span.indices, expected.utf8.indices) {
+      expectEqual(span[i], expected.utf8[j])
+    }
+  }
+}