Emit compile-time error for incorrectly used optional parameters.

sdk/lib/_internal/compiler/implementation/warnings.dart

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
diff --git a/sdk/lib/_internal/compiler/implementation/warnings.dart b/sdk/lib/_internal/compiler/implementation/warnings.dart
index 5a8ae00f3f5ed7358b3866a95dc3160e00bbf8ed..3f60bd31abb44bcfacf6aeb83ec0afc67d359c29 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -418,6 +418,37 @@ main() => new C(0);"""]);
   static const MessageKind CANNOT_INSTANTIATE_TYPEDEF = const MessageKind(
       'Error: Cannot instantiate typedef "#{typedefName}".');
 
+  static const MessageKind REQUIRED_PARAMETER_WITH_DEFAULT = const MessageKind(
+      "Error: Non-optional parameters can't have default a value.",
+      howToFix: "Remove the default value or make the parameter optional.",

[ahe, 2013/09/13 07:17:05]

"Remove ..." sound like a command/order, could you make it sound more like a
suggestion?

+      examples: const ["""
+main() {
+  foo(a: 1) => print(a);
+  foo(2);
+}""", """
+main() {
+  foo(a = 1) => print(a);
+  foo(2);
+}"""]);
+
+  static const MessageKind NAMED_PARAMETER_WITH_EQUALS = const MessageKind(
+      "Error: Named parameters must use ':'.",

[ahe, 2013/09/13 07:17:05]

I have a suspicion that Luke would say this error message is a bit rude ;-)

How about: "A named parameter can't be followed by '=', a default value of a
named parameter is indicated with ':'."

As far as I understand Luke's advice, this follows the guide line: what is wrong
and why?

+      howToFix: "Change '=' to ':'",

[ahe, 2013/09/13 07:17:05]

Suggestion?

+      examples: const ["""
+main() {
+  foo({a = 1}) => print(a);
+  foo(a: 2);
+}"""]);
+
+  static const MessageKind POSITIONAL_PARAMETER_WITH_EQUALS = const MessageKind(
+      "Error: Positional optional parameters must use '='.",

[ahe, 2013/09/13 07:17:05]

Possibly rude, see above. 

+      howToFix: "Change ':' to '='",

[ahe, 2013/09/13 07:17:05]

Suggestion?

+      examples: const ["""
+main() {
+  foo([a: 1]) => print(a);
+  foo(2);
+}"""]);
+
   static const MessageKind TYPEDEF_FORMAL_WITH_DEFAULT = const MessageKind(
       "Error: A parameter of a typedef can't specify a default value.",
       howToFix: "Remove the default value.",