gistfile1.cs

// <Name>Do not hide base class methods</Name>
// Prefer override virtual methods
// More on hiding vs. virtual usefulness here:
//  http://www.artima.com/intv/nonvirtual.html
//  http://blogs.msdn.com/b/ericlippert/archive/2008/05/21/method-hiding-apologia.aspx

warnif count > 0

// Define lookup table indexing methods by their name including parameters signature.
let lookup = Methods.Where(m => !m.IsConstructor && !m.IsStatic && !m.IsGeneratedByCompiler)
                    .ToLookup(m1 => m1.Name)

from t in Application.Types
where !t.IsStatic && t.IsClass &&
   // Discard classes deriving directly from System.Object
   t.DepthOfInheritance > 1 
where t.BaseClasses.Any()

// For each methods not overriding any methods (new slot), 
// let's check if it hides by name some methods defined in base classe.
from m in t.InstanceMethods
where m.IsNewSlot && !m.IsExplicitInterfaceImpl && !m.IsGeneratedByCompiler

// Notice how lookup is used to quickly retrieve methods with same name as m.
// This makes the query 10 times faster than iterating each base methods to check their name.
let baseMethodsHidden = lookup[m.Name].Where(m1 => m1 != m && t.DeriveFrom(m1.ParentType))

where baseMethodsHidden.Count() > 0
select new { m, baseMethodsHidden }