SE-0066: Added error and fixit for non-parenthesized function param types

Author: Harlan Haskins

include/swift/AST/DiagnosticsParse.def

@@ -615,6 +615,8 @@ ERROR(expected_type_before_arrow,none,
       "expected type before '->'", ())
 ERROR(expected_type_after_arrow,none,
       "expected type after '->'", ())
+ERROR(non_tuple_function_param_type,none,
+      "type before '->' must be wrapped in parentheses", ())
 
 // Enum Types
 ERROR(expected_expr_enum_case_raw_value,PointsToFirstBadToken,

lib/Parse/ParseType.cpp

@@ -187,6 +187,12 @@ ParserResult<TypeRepr> Parser::parseType(Diag<> MessageID,
   // Handle type-function if we have an arrow.
   SourceLoc arrowLoc;
   if (consumeIf(tok::arrow, arrowLoc)) {
+    if (!isa<TupleTypeRepr>(ty.get())) {
+      diagnose(ty.get()->getStartLoc(), diag::non_tuple_function_param_type)
+        .highlight(ty.get()->getSourceRange())
+        .fixItInsert(ty.get()->getStartLoc(), "(")
+        .fixItInsertAfter(ty.get()->getEndLoc(), ")");
+    }
     ParserResult<TypeRepr> SecondHalf =
       parseType(diag::expected_type_function_result);
     if (SecondHalf.hasCodeCompletion())