Fix bug with optional string params (#1767)

Author: liamappelbe

pkgs/swift2objc/lib/src/transformer/_core/utils.dart

@@ -66,7 +66,12 @@ import 'unique_namer.dart';
       return (value, type);
     }
   } else if (type is OptionalType) {
-    final (newValue, newType) = maybeUnwrapValue(type.child, '$value?');
+    final optValue = '$value?';
+    var (newValue, newType) = maybeUnwrapValue(type.child, optValue);
+    if (newValue == optValue) {
+      // newValue is value?, so the ? isn't necessary and causes compile errors.
+      newValue = value;
+    }
     return (newValue, OptionalType(newType));
   } else {
     throw UnimplementedError('Unknown type: $type');

pkgs/swift2objc/test/integration/optional_input.swift

@@ -1,11 +1,11 @@
 import Foundation
 
-// public func funcOptionalPrimitiveReturn() -> Int? { return 123 }
 public func funcOptionalClassReturn() -> MyClass? { return MyClass(label: nil) }
 public func funcOptionalStructReturn() -> MyStruct? { return nil }
 public func funcOptionalArgs(label param: MyClass?) -> MyClass { return param! }
 public func funcMultipleOptionalArgs(
     label1 param1: MyClass?,label2 param2: Int, label3 param3: MyStruct?){}
+public func funcOptionalStrings(str: String?) -> String? { return str; }
 
 public var globalOptional: MyStruct?
 

pkgs/swift2objc/test/integration/optional_output.swift

@@ -17,6 +17,10 @@ import Foundation
     return MyClassWrapper(result)
   }
 
+  @objc static public func funcOptionalStringsWrapper(str: String?) -> String? {
+    return funcOptionalStrings(str: str)
+  }
+
   @objc static public func funcOptionalClassReturnWrapper() -> MyClassWrapper? {
     let result = funcOptionalClassReturn()
     return result == nil ? nil : MyClassWrapper(result!)