A Simple Aspect for NHibernate and the virtual keyword

#region License

// Copyright (c) 2008, Michal Dabrowski
// 
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
// 
//     * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
//     * Neither the name of the Michal Dabrowski nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#endregion

using System.Collections.Generic;
using System.Reflection;
using PostSharp.CodeModel;
using PostSharp.CodeWeaver;
using PostSharp.Extensibility;
using PostSharp.Extensibility.Tasks;

namespace Unsealer.Weaver {
    public class UnsealTask : Task, IAdviceProvider {
        #region IAdviceProvider Members

        public void ProvideAdvices(PostSharp.CodeWeaver.Weaver codeWeaver) {
            CustomAttributeDictionaryTask task = CustomAttributeDictionaryTask.GetTask(this.Project);

            IEnumerator<ICustomAttributeInstance> customAttributesEnumerator = task.GetCustomAttributesEnumerator(typeof (UnsealAttribute), false);

            while (customAttributesEnumerator.MoveNext()) {
                var wovenType = customAttributesEnumerator.Current.TargetElement as TypeDefDeclaration;

                if ((wovenType != null) && (! wovenType.IsInterface())) {
                    if (wovenType.IsSealed()) {
                        MessageSource.MessageSink.Write(new Message(SeverityType.Error, "UNSL01", string.Format("Unsealer cannot process the type '{0}' because it is sealed. Remove either the 'sealed' keyword or the [Unseal] attribute.", wovenType.Name), "Unsealer"));
                    }

                    foreach (var method in wovenType.Methods) {
                        if (method.IsInstance() && method.IsNonPrivate() && (method.Name != ".ctor") && (!method.IsVirtual())) {
                            if (method.IsSealed()) {
                                MessageSource.MessageSink.Write(new Message(SeverityType.Error, "UNSL02", string.Format("Unsealer cannot process the method '{0}' in type '{1}' because it is sealed. Remove either the 'sealed' keyword from the method or the [Unseal] attribute from its declaring type.", method.Name, wovenType.Name), "Unsealer"));
                            }

                            method.Attributes |= MethodAttributes.Virtual | MethodAttributes.NewSlot;
                        }
                    }
                }
            }
        }

        #endregion
    }
}