In strong mode, properly infer the return types of setters as `void`

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart

 // Copyright (c) 2017, 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.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 1500 matching lines @@
   }
 
   static MethodNode getMethodNode(Procedure procedure) {
     if (procedure is KernelProcedure) return procedure._methodNode;
     return null;
   }
 
   static bool hasImplicitReturnType(KernelProcedure procedure) {
     return procedure._hasImplicitReturnType;
   }
+
+  static void inferSetterReturnType(
+      KernelProcedure procedure, TypeInferenceEngineImpl engine, String uri) {
+    assert(procedure.isSetter);
+    if (procedure._hasImplicitReturnType) {
+      var inferredType = const VoidType();
+      engine.instrumentation?.record(Uri.parse(uri), procedure.fileOffset,
+          'topType', new InstrumentationValueForType(inferredType));
+      procedure.function?.returnType = inferredType;
+    }
+  }
 }
 
 /// Concrete shadow object representing an assignment to a property.
 class KernelPropertyAssign extends KernelComplexAssignmentWithReceiver {
   /// If this assignment uses null-aware access (`?.`), the conditional
   /// expression that guards the access; otherwise `null`.
   Expression nullAwareGuard;
 
   KernelPropertyAssign(Expression receiver, Expression rhs,
       {bool isSuper: false})
@@ skipping 773 matching lines @@
   }
 
   transformChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 
   visitChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 }