[Parser] Adds a fix-it to convert the subscript into two arrays

Author: theblixguy

include/swift/AST/DiagnosticsParse.def

@@ -763,7 +763,9 @@ ERROR(extra_rbracket,PointsToFirstBadToken,
 ERROR(extra_colon,PointsToFirstBadToken,
       "unexpected ':' in type; did you mean to write a dictionary type?", ())
 WARNING(subscript_collection_element_invalid_index, none,
-       "index '%0' in subscript expression is out of bounds", (StringRef))
+        "index '%0' in subscript expression is out of bounds", (StringRef))
+NOTE(subscript_collection_element_fix_it, none, "did you mean to write two "
+     "array literals instead?", ())
 
 // Tuple Types
 ERROR(expected_rparen_tuple_type_list,none,

lib/Parse/ParseExpr.cpp

@@ -3509,6 +3509,12 @@ void Parser::validateCollectionElement(ParserResult<Expr> element) {
                          diag::subscript_collection_element_invalid_index,
                          indexExpr->getDigitsText());
     diag.highlight(subscriptExpr->getSourceRange());
+    diag.flush();
+
+    auto note = diagnose(subscriptExpr->getLoc(),
+                         diag::subscript_collection_element_fix_it);
+    note.fixItInsertAfter(baseExpr->getRBracketLoc(), ",");
+
     element.setIsParseError();
   }
 }

test/type/array.swift

@@ -117,6 +117,6 @@ func passAssocType<T : HasAssocType>(_ t: T) {
 // SR-11134
 
 let sr_11134_1 = [["a"][0]] // Ok
-let sr_11134_2 = [["a"][1]] // expected-warning {{index '1' in subscript expression is out of bounds}}
+let sr_11134_2 = [["a"][1]] // expected-warning {{index '1' in subscript expression is out of bounds}} // expected-note {{did you mean to write two array literals instead?}}{{24-24=,}}
+let sr_11134_3 = [[1, 1, 1], [], [4, 5, 6, 7], [0], [], [] [42]] // expected-warning {{index '42' in subscript expression is out of bounds}} // expected-note {{did you mean to write two array literals instead?}}{{59-59=,}}
 
-let sr_11134_3 = [[1, 1, 1], [], [4, 5, 6, 7], [0], [], [] [42]] // expected-warning {{index '42' in subscript expression is out of bounds}}