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//
// AvoidMessageChainsRule class
//
// Authors:
// Néstor Salceda <nestor.salceda@gmail.com>
// Sebastien Pouliot <sebastien@ximian.com>
//
// (C) 2008 Néstor Salceda
// Copyright (C) 2008 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using Mono.Cecil;
using Mono.Cecil.Cil;
using Gendarme.Framework;
using Gendarme.Framework.Engines;
using Gendarme.Framework.Helpers;
using Gendarme.Framework.Rocks;
namespace Gendarme.Rules.Smells {
// TODO: It may be worthwhile mentioning the law of demeter. The summary
// doesn't really say what the message chain smell is. The summary could do a better
// job explaining why the coupling is harmful (changes to the object inter-relationships
// can cause cascading changes to the source code). It would be helpful if the summary
// explained how to fix the problem (e.g. by adding accessors to encapsulate the structure).
// The good example is not a good version of the bad example (it should call a ToFrench
// or maybe a Language method on a person object).
/// <summary>
/// This rule checks for the Message Chain smell. This can cause problems because it
/// means that your code is heavily coupled to the navigation structure.
/// </summary>
/// <example>
/// Bad example:
/// <code>
/// public void Method (Person person)
/// {
/// person.GetPhone ().GetAreaCode ().GetCountry ().Language.ToFrench ("Hello world");
/// }
/// </code>
/// </example>
/// <example>
/// Good example:
/// <code>
/// public void Method (Language language)
/// {
/// language.ToFrench ("Hello world");
/// }
/// </code>
/// </example>
[Problem ("The code contains long sequences of method calls: this means your code is heavily coupled to the navigation structure.")]
[Solution ("You can apply the Hide Delegate refactoring or Extract Method to push down the chain.")]
[EngineDependency (typeof (OpCodeEngine))]
public class AvoidMessageChainsRule : Rule, IMethodRule {
private int maxChainLength = 4;
public int MaxChainLength {
get {
return maxChainLength;
}
set {
maxChainLength = value;
}
}
// this mask represents Callvirt, Call, Newobj and Newarr
static OpCodeBitmask chain = new OpCodeBitmask (0x8000000000, 0x4400000000000, 0x400, 0x0);
public RuleResult CheckMethod (MethodDefinition method)
{
if (!method.HasBody)
return RuleResult.DoesNotApply;
// no chain are possible without Call[virt] instructions within the method
OpCodeBitmask calls = OpCodeBitmask.Calls;
if (!calls.Intersect (OpCodeEngine.GetBitmask (method)))
return RuleResult.DoesNotApply;
Log.WriteLine (this);
Log.WriteLine (this, "-------------------------------------");
Log.WriteLine (this, method);
// walk back so we don't process very long chains multiple times
// (we don't need to go down to zero since it would not be big enough for a chain to exists)
IList<Instruction> ic = method.Body.Instructions;
for (int i = ic.Count - 1; i >= MaxChainLength; i--) {
Instruction ins = ic [i];
// continue until we find a Call[virt] instruction
if (!calls.Get (ins.OpCode.Code))
continue;
// operators "break" chains
MethodReference mr = (ins.Operand as MethodReference);
if (mr.Name.StartsWith ("op_", StringComparison.Ordinal))
continue;
int counter = 1;
// trace back every call (including new objects and arrays) and
// check if the caller is a call (i.e. not a local)
Instruction caller = ins.TraceBack (method);
while ((caller != null) && ValidLink (caller)) {
counter++;
i = ic.IndexOf (caller);
caller = caller.TraceBack (method);
}
Log.WriteLine (this, "chain of length {0} at {1:X4}", counter, ins.Offset);
if (counter > MaxChainLength) {
string msg = String.Format (CultureInfo.CurrentCulture,
"Chain length {0} versus maximum of {1}.", counter, MaxChainLength);
Runner.Report (method, ins, Severity.Medium, Confidence.Normal, msg);
}
}
return Runner.CurrentRuleResult;
}
static private bool ValidLink (Instruction ins)
{
bool valid = false;
if (chain.Get (ins.OpCode.Code)) {
// static method calls terminate chains
MethodReference mr = ins.Operand as MethodReference;
if (mr != null) {
MethodDefinition method = mr.Resolve();
if (method != null && !method.IsStatic)
valid = true;
} else
valid = true; // should be Newobj or Newarr
}
return valid;
}
}
}
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