[Reflection] Handle -disable-reflection-names in _forEachField.

Invoke our callback with an empty name string when reflection names are disabled, rather than throwing a fatal error.

rdar://108709009

Author: mikeash

stdlib/public/core/ReflectionMirror.swift

@@ -284,8 +284,14 @@ public func _forEachField(
     defer { field.freeFunc?(field.name) }
     let kind = _MetadataKind(childType)
 
-    if !body(field.name!, offset, childType, kind) {
-      return false
+    if let name = field.name {
+      if !body(name, offset, childType, kind) {
+        return false
+      }
+    } else {
+      if !body("", offset, childType, kind) {
+        return false
+      }
     }
   }
 
@@ -362,8 +368,14 @@ public func _forEachFieldWithKeyPath<Root>(
         endOfReferencePrefix: false)
     }
 
-    if !body(field.name!, partialKeyPath) {
-      return false
+    if let name = field.name {
+      if !body(name, partialKeyPath) {
+        return false
+      }
+    } else {
+      if !body("", partialKeyPath) {
+        return false
+      }
     }
   }
 

test/stdlib/ForEachField.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 // RUN: %target-run-simple-swift
+// RUN: %target-run-simple-swift(-Xfrontend -disable-reflection-names -DNO_FIELD_NAMES)
 // REQUIRES: executable_test
 // REQUIRES: reflection
 
@@ -150,6 +151,14 @@ func checkFields<T>(
     count += 1
 
     let fieldName = String(cString: charPtr)
+    if fieldName == "" {
+#if NO_FIELD_NAMES
+      expectTrue(fields.values.contains{ $0 == offset && $1 == type })
+#else
+      expectTrue(false, "Empty field name")
+#endif
+      return true
+    }
     guard let (checkOffset, checkType) = fields[fieldName] else {
       expectTrue(false, "Unexpected field '\(fieldName)'")
       return true
@@ -176,6 +185,14 @@ func checkFieldsWithKeyPath<T>(
     count += 1
 
     let fieldName = String(cString: charPtr)
+    if fieldName == "" {
+#if NO_FIELD_NAMES
+      expectTrue(fields.values.contains{ $0 == keyPath })
+#else
+      expectTrue(false, "Empty field name")
+#endif
+      return true
+    }
     guard let checkKeyPath = fields[fieldName] else {
       expectTrue(false, "Unexpected field '\(fieldName)'")
       return true
@@ -450,8 +467,13 @@ if #available(SwiftStdlib 5.2, *) {
       charPtr, _, type, _ in
 
       let fieldName = String(cString: charPtr)
+    #if NO_FIELD_NAMES
+      return type == (Double, Double).self
+        && fieldName == ""
+    #else
       return type == (Double, Double).self
         && fieldName == "point"
+    #endif
     })
 
     expectTrue(_forEachField(of: EmptyNSObject.self, options: .classType) {