Report a compile-time error when a setter has not exactly one formal parameter.

sdk/lib/_internal/compiler/implementation/resolution/members.dart

Index: sdk/lib/_internal/compiler/implementation/resolution/members.dart
diff --git a/sdk/lib/_internal/compiler/implementation/resolution/members.dart b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
index d30753dff35e6085cc95390c894ce77d827477dd..f5f10ba0184aab80d3b2c4b11229d2cdf49005f9 100644
--- a/sdk/lib/_internal/compiler/implementation/resolution/members.dart
+++ b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
@@ -3038,6 +3038,15 @@ class SignatureResolver extends CommonResolverVisitor<Element> {
       parameters = parametersBuilder.toLink();
     }
     DartType returnType = compiler.resolveReturnType(element, returnNode);

[ngeoffray, 2012/12/09 20:44:00]

This can move line 3050.

+    if (element.isSetter() && (requiredParameterCount != 1 ||
+                               visitor.optionalParameterCount != 0)) {
+      // If there are no formal parameters, we already reported an error above.

[ngeoffray, 2012/12/09 20:44:00]

Somehow this looks a bit brittle. Could you instead switch on the element kind
and report errors for each?

+      if (formalParameters != null) {
+        compiler.reportMessage(compiler.spanFromNode(formalParameters),
+                               MessageKind.ILLEGAL_SETTER_FORMALS.error([]),
+                               Diagnostic.ERROR);
+      }
+    }
     return new FunctionSignature(parameters,
                                  visitor.optionalParameters,
                                  requiredParameterCount,