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//
// Gendarme.Rules.Performance.DontIgnoreMethodResultRule
//
// Authors:
// Lukasz Knop <lukasz.knop@gmail.com>
// Sebastien Pouliot <sebastien@ximian.com>
//
// Copyright (C) 2007 Lukasz Knop
// Copyright (C) 2007-2008 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 Mono.Cecil;
using Mono.Cecil.Cil;
using Gendarme.Framework;
using Gendarme.Framework.Engines;
using Gendarme.Framework.Helpers;
using Gendarme.Framework.Rocks;
namespace Gendarme.Rules.Performance {
/// <summary>
/// This rule fires if a method is called that returns a new instance but that instance
/// is not used. This is a performance problem because it is wasteful to create and
/// collect objects which are never actually used. It may also indicate a logic problem.
/// Note that this rule currently only checks methods within a small number of System
/// types.
/// </summary>
/// <example>
/// Bad example:
/// <code>
/// public void GetName ()
/// {
/// string name = Console.ReadLine ();
/// // This is a bug: strings are (mostly) immutable so Trim leaves
/// // name untouched and returns a new string.
/// name.Trim ();
/// Console.WriteLine ("Name: {0}", name);
/// }
/// </code>
/// </example>
/// <example>
/// Good example:
/// <code>
/// public void GetName ()
/// {
/// string name = Console.ReadLine ();
/// name = name.Trim ();
/// Console.WriteLine ("Name: {0}", name);
/// }
/// </code>
/// </example>
[Problem ("The method ignores the result value from a method call.")]
[Solution ("Don't ignore the result value.")]
[EngineDependency (typeof (OpCodeEngine))]
[FxCopCompatibility ("Microsoft.Usage", "CA1806:DoNotIgnoreMethodResults")]
public class DoNotIgnoreMethodResultRule : Rule, IMethodRule {
public RuleResult CheckMethod (MethodDefinition method)
{
// rule only applies if the method has a body
// rule doesn't not apply to generated code (out of developer's control)
if (!method.HasBody || method.IsGeneratedCode ())
return RuleResult.DoesNotApply;
// check if the method contains a Pop instruction
if (!OpCodeEngine.GetBitmask (method).Get (Code.Pop))
return RuleResult.DoesNotApply;
foreach (Instruction instruction in method.Body.Instructions) {
if (instruction.OpCode.Code == Code.Pop) {
CheckForViolation (method, instruction.Previous);
}
}
return Runner.CurrentRuleResult;
}
private static bool IsCallException (MethodReference method)
{
switch (method.DeclaringType.FullName) {
case "System.String":
// Since strings are immutable, calling System.String methods that returns strings
// better be assigned to something
return (method.ReturnType.ReturnType.FullName != "System.String");
case "System.IO.DirectoryInfo":
// GetDirectories overloads don't apply to the instance
return (method.Name != "GetDirectories");
case "System.Security.PermissionSet":
// Intersection and Union returns a new PermissionSet (it does not change the instance)
return (method.ReturnType.ReturnType.FullName != "System.Security.PermissionSet");
default:
// this is useless anytime, if unassigned, more in cases like a StringBuilder
return (method.Name != "ToString");
}
}
private static bool IsNewException (MemberReference method)
{
switch (method.ToString ()) {
// supplying a callback is enough to make the Timer creation worthwhile
case "System.Void System.Threading.Timer::.ctor(System.Threading.TimerCallback,System.Object,System.Int32,System.Int32)":
return true;
default:
return false;
}
}
private void CheckForViolation (MethodDefinition method, Instruction instruction)
{
if ((instruction.OpCode.Code == Code.Newobj || instruction.OpCode.Code == Code.Newarr)) {
MemberReference member = (instruction.Operand as MemberReference);
if ((member != null) && !IsNewException (member)) {
string s = String.Format ("Unused object of type '{0}' created.", member.ToString ());
Runner.Report (method, instruction, Severity.High, Confidence.Normal, s);
}
}
if (instruction.OpCode.Code == Code.Call || instruction.OpCode.Code == Code.Callvirt) {
MethodReference callee = instruction.Operand as MethodReference;
if (callee != null && !callee.ReturnType.ReturnType.IsValueType) {
// check for some common exceptions (to reduce false positive)
if (!IsCallException (callee)) {
string s = String.Format ("Do not ignore method results from call to '{0}'.", callee.ToString ());
Runner.Report (method, instruction, Severity.Medium, Confidence.Normal, s);
}
}
}
}
}
}
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