[Sema] Improve type coercion fixits for optional-to-optional conversions.

lib/Sema/CSDiag.cpp

@@ -2869,6 +2869,10 @@ static bool addTypeCoerceFixit(InFlightDiagnostic &diag, ConstraintSystem &CS,
                                Type fromType, Type toType, Expr *expr) {
   // Look through optional types; casts can add them, but can't remove extra
   // ones.
+  bool bothOptional =
+      fromType->getOptionalObjectType() && toType->getOptionalObjectType();
+  if (bothOptional)
+    fromType = fromType->getOptionalObjectType();
   toType = toType->lookThroughAllOptionalTypes();
 
   CheckedCastKind Kind = CS.getTypeChecker().typeCheckCheckedCast(
@@ -2877,9 +2881,11 @@ static bool addTypeCoerceFixit(InFlightDiagnostic &diag, ConstraintSystem &CS,
   if (Kind != CheckedCastKind::Unresolved) {
     SmallString<32> buffer;
     llvm::raw_svector_ostream OS(buffer);
-    toType->print(OS);
     bool canUseAs = Kind == CheckedCastKind::Coercion ||
       Kind == CheckedCastKind::BridgingCoercion;
+    if (bothOptional && canUseAs)
+      toType = OptionalType::get(toType);
+    toType->print(OS);
     diag.fixItInsert(
         Lexer::getLocForEndOfToken(CS.DC->getASTContext().SourceMgr,
                                    expr->getEndLoc()),

test/Constraints/bridging.swift

@@ -276,30 +276,34 @@ func rdar19831698() {
 // <rdar://problem/19836341> Incorrect fixit for NSString? to String? conversions
 func rdar19836341(_ ns: NSString?, vns: NSString?) {
   var vns = vns
-  let _: String? = ns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}
-  var _: String? = ns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}
-  // FIXME: there should be a fixit appending "as String?" to the line; for now
-  // it's sufficient that it doesn't suggest appending "as String"
+  let _: String? = ns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}{{22-22= as String?}}
+  var _: String? = ns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}{{22-22= as String?}}
 
   // Important part about below diagnostic is that from-type is described as
   // 'NSString?' and not '@lvalue NSString?':
-  let _: String? = vns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}
-  var _: String? = vns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}
-  
+  let _: String? = vns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}{{23-23= as String?}}
+  var _: String? = vns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}{{23-23= as String?}}
+
   vns = ns
 }
 
 // <rdar://problem/20029786> Swift compiler sometimes suggests changing "as!" to "as?!"
 func rdar20029786(_ ns: NSString?) {
-  var s: String = ns ?? "str" as String as String // expected-error{{cannot convert value of type 'NSString?' to expected argument type 'String?'}}
-  var s2 = ns ?? "str" as String as String // expected-error {{cannot convert value of type 'String' to expected argument type 'NSString'}}
+  var s: String = ns ?? "str" as String as String // expected-error{{cannot convert value of type 'NSString?' to expected argument type 'String?'}}{{21-21= as String?}}
+  var s2 = ns ?? "str" as String as String // expected-error {{cannot convert value of type 'String' to expected argument type 'NSString'}}{{43-43= as NSString}}
 
-  let s3: NSString? = "str" as String? // expected-error {{cannot convert value of type 'String?' to specified type 'NSString?'}}
+  let s3: NSString? = "str" as String? // expected-error {{cannot convert value of type 'String?' to specified type 'NSString?'}}{{39-39= as NSString?}}
 
-  var s4: String = ns ?? "str" // expected-error{{cannot convert value of type 'NSString' to specified type 'String'}}
+  var s4: String = ns ?? "str" // expected-error{{cannot convert value of type 'NSString' to specified type 'String'}}{{31-31= as String}}
   var s5: String = (ns ?? "str") as String // fixed version
 }
 
+// Make sure more complicated cast has correct parenthesization
+func castMoreComplicated(anInt: Int?) {
+  let _: (NSObject & NSCopying)? = anInt // expected-error{{cannot convert value of type 'Int?' to specified type '(NSObject & NSCopying)?'}}{{41-41= as (NSObject & NSCopying)?}}
+}
+
+
 // <rdar://problem/19813772> QoI: Using as! instead of as in this case produces really bad diagnostic
 func rdar19813772(_ nsma: NSMutableArray) {
   var a1 = nsma as! Array // expected-error{{generic parameter 'Element' could not be inferred in cast to 'Array'}} expected-note {{explicitly specify the generic arguments to fix this issue}} {{26-26=<Any>}}

test/FixCode/fixits-apply-objc.swift.result

@@ -18,5 +18,5 @@ func foo1(_ an : Any) {
 }
 
 func foo2(_ messageData: Any?) -> AnyObject? {
-  return messageData as AnyObject
+  return messageData as AnyObject?
 }