Complain about bad operator parameters.

pkg/front_end/lib/src/fasta/source/outline_builder.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.outline_builder;
 
 import 'package:kernel/ast.dart' show AsyncMarker, ProcedureKind;
 
 import '../fasta_codes.dart' show FastaMessage, codeExpectedBlockToSkip;
 
@@ skipping 13 matching lines @@
 
 import '../modifier.dart' show Modifier;
 
 import 'source_library_builder.dart' show SourceLibraryBuilder;
 
 import 'unhandled_listener.dart' show NullValue, Unhandled, UnhandledListener;
 
 import '../parser/dart_vm_native.dart'
     show removeNativeClause, skipNativeClause;
 
-import '../operator.dart' show Operator, operatorFromString, operatorToString;
+import '../operator.dart'
+    show
+        Operator,
+        operatorFromString,
+        operatorToString,
+        operatorRequiredArgumentCount;
 
 import '../quote.dart' show unescapeString;
 
 enum MethodBody {
   Abstract,
   Regular,
   RedirectingFactoryBody,
 }
 
 AsyncMarker asyncMarkerFromTokens(Token asyncToken, Token starToken) {
@@ skipping 317 matching lines @@
     int charOffset = pop();
     dynamic nameOrOperator = pop();
     if (Operator.subtract == nameOrOperator && formals == null) {
       nameOrOperator = Operator.unaryMinus;
     }
     String name;
     ProcedureKind kind;
     if (nameOrOperator is Operator) {
       name = operatorToString(nameOrOperator);
       kind = ProcedureKind.Operator;
+      int requiredArgumentCount = operatorRequiredArgumentCount(nameOrOperator);
+      if ((formals?.length ?? 0) != requiredArgumentCount) {
+        library.addCompileTimeError(
+            charOffset,
+            "Operator '$name' must have exactly $requiredArgumentCount "
+            "parameters.");
+      } else {
+        if (formals != null) {
+          for (FormalParameterBuilder formal in formals) {
+            if (!formal.isRequired) {
+              library.addCompileTimeError(formal.charOffset,
+                  "An operator can't have optional parameters.");
+            }
+          }
+        }
+      }
     } else {
       name = nameOrOperator;
       kind = computeProcedureKind(getOrSet);
     }
     TypeBuilder returnType = pop();
     int modifiers =
         Modifier.validate(pop(), isAbstract: bodyKind == MethodBody.Abstract);
     List<MetadataBuilder> metadata = pop();
     library.addProcedure(
         metadata,
@@ skipping 415 matching lines @@
   Link<Token> handleMemberName(Link<Token> identifiers) {
     if (!isDartLibrary || identifiers.isEmpty) return identifiers;
     return removeNativeClause(identifiers);
   }
 
   @override
   void debugEvent(String name) {
     // printEvent(name);
   }
 }