Make sure SwiftObject doesn't crash when compared to tagged pointers (#83269)

Fixes rdar://152912840

Author: Catfish-Man

stdlib/public/runtime/SwiftObject.mm

@@ -438,7 +438,13 @@ - (BOOL)isEqual:(id)other {
     // Legacy behavior: Don't proxy to Swift Hashable or Equatable
     return NO; // We know the ids are different
   }
-
+  if (isObjCTaggedPointer(other)) {
+    // Swift class types cannot be tagged, and a Swift Equatable conformance
+    // cannot validly be called for an object of a different type, so this can
+    // only be incorrect if someone has an Equatable that's invalid in an
+    // extremely specific way (unsafeBitCasting `other` to an unrelated type)
+    return NO;
+  }
 
   // Get Swift type for self and other
   auto selfMetadata = _swift_getClassOfAllocated(self);

test/stdlib/BridgeEquatableToObjC.swift

@@ -22,6 +22,10 @@ struct MyNonEquatableStruct {
   var text: String
 }
 
+class MyEquatableClass: Equatable {
+  static func == (lhs: MyEquatableClass, rhs: MyEquatableClass) -> Bool { true }
+}
+
 BridgeEquatableToObjC.test("Bridge equatable struct") {
   let swiftA = MyEquatableStruct(text: "xABC")
   let swiftB = swiftA
@@ -46,5 +50,13 @@ BridgeEquatableToObjC.test("Bridge non-equatable struct") {
   expectEqual(objcResult, false)
 }
 
+BridgeEquatableToObjC.test("Compare tagged pointer to equatable SwiftObject") {
+  let literal = "The quick brown fox jumps over the lazy dog"
+  let bridgedLiteral = literal as NSString
+  let foo = MyEquatableClass()
+  let bridgedFoo = foo as AnyObject
+  let result = bridgedFoo.isEqual(bridgedLiteral)
+  expectEqual(result, false)
+}
 
 runAllTests()