Improve type coercion fixits for optional-to-optional conversions.

Author: gregomni

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(
@@ -2883,7 +2887,8 @@ static bool addTypeCoerceFixit(InFlightDiagnostic &diag, ConstraintSystem &CS,
     diag.fixItInsert(
         Lexer::getLocForEndOfToken(CS.DC->getASTContext().SourceMgr,
                                    expr->getEndLoc()),
-        (llvm::Twine(canUseAs ? " as " : " as! ") + OS.str()).str());
+        (llvm::Twine(canUseAs ? " as " : " as! ") + OS.str() +
+         llvm::Twine(canUseAs && bothOptional ? "?" : "")).str());
     return true;
   }
   return false;

test/Constraints/bridging.swift

@@ -276,27 +276,25 @@ 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
 }