Stop supporting map literals with 1 type argument

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 17246)
+++ runtime/vm/parser.cc	(working copy)
@@ -27,8 +27,6 @@
 DEFINE_FLAG(bool, trace_parser, false, "Trace parser operations.");
 DEFINE_FLAG(bool, warning_as_error, false, "Treat warnings as errors.");
 DEFINE_FLAG(bool, silent_warnings, false, "Silence warnings.");
-DEFINE_FLAG(bool, warn_legacy_map_literal, false,
-            "Warning on legacy map literal syntax (single type argument)");
 
 static void CheckedModeHandler(bool value) {
   FLAG_enable_asserts = value;
@@ -8638,30 +8636,17 @@
   if (!map_type_arguments.IsNull()) {
     ASSERT(map_type_arguments.Length() > 0);
     // Map literals take two type arguments.
-    if (map_type_arguments.Length() < 2) {
-      // TODO(hausner): Remove legacy syntax support.
-      // We temporarily accept a single type argument.
-      if (FLAG_warn_legacy_map_literal) {
-        Warning(type_pos,
-                "a map literal takes two type arguments specifying "
-                "the key type and the value type");
-      }
-      TypeArguments& type_array = TypeArguments::Handle(TypeArguments::New(2));
-      type_array.SetTypeAt(0, Type::Handle(Type::StringType()));
-      type_array.SetTypeAt(1, value_type);
-      map_type_arguments = type_array.raw();
-    } else if (map_type_arguments.Length() > 2) {
+    if (map_type_arguments.Length() != 2) {
       ErrorMsg(type_pos,
                "a map literal takes two type arguments specifying "
                "the key type and the value type");
-    } else {
-      const AbstractType& key_type =
-          AbstractType::Handle(map_type_arguments.TypeAt(0));
-      value_type = map_type_arguments.TypeAt(1);
-      if (!key_type.IsStringType()) {
-        ErrorMsg(type_pos, "the key type of a map literal must be 'String'");
-      }
     }
+    const AbstractType& key_type =
+        AbstractType::Handle(map_type_arguments.TypeAt(0));
+    value_type = map_type_arguments.TypeAt(1);
+    if (!key_type.IsStringType()) {
+      ErrorMsg(type_pos, "the key type of a map literal must be 'String'");
+    }
     if (is_const && !value_type.IsInstantiated()) {
       ErrorMsg(type_pos,
                "the type argument of a constant map literal cannot include "