Gendarme Tasks. Weekly Status Report #4

June 23, 2007

This is the status report for June 18 - June 23

Accomplished this week:

This week I have continued with the Code Duplicated smell. I'm trying detect duplicated code reading IL instructions and checking against others. Is a simple approach and I can detect some code duplicate. I'm also impressed with Cecil, it's a great library and I love the Visitor pattern.

But I'm not happy with the results, because detecting branches is difficult and I can't detect all code ways.

By example: Suppose a simple if statement:

if (myList.Contains ("MoreFoo"))
        myList.Remove ("MoreFoo");

The IL Code generated is the following:

IL_0000:  ldarg.0
IL_0001:  ldfld class [mscorlib]System.Collections.IList Test.Rules.Smells.ClassWithCodeDuplicated::myList
IL_0006:  ldstr "MoreFoo"
IL_000b:  callvirt instance bool class [mscorlib]System.Collections.IList::Contains(object)
IL_0010:  brfalse IL_0025

IL_0015:  ldarg.0
IL_0016:  ldfld class [mscorlib]System.Collections.IList Test.Rules.Smells.ClassWithCodeDuplicated::myList
IL_001b:  ldstr "MoreFoo"
IL_0020:  callvirt instance void class [mscorlib]System.Collections.IList::Remove(object)
IL_0025:  ret

I drop out the ldarg, ldfld, ldstr and others, and I get the information for compare Instruction Pairs. And If I write only:

myList.Contains ("MoreFoo");
myList.Remove ("MoreFoo");

The unique difference in the IL code was that I haven't the branch instruction. I can detect simple duplications, but only detecting these ones won't be useful.

Then I decided:

Plans for the next week.

Following the last lines, I have decided change the code representation, and I will use Control Flow Graphs for make some FlowAnalysis and obtain more information for detect code complete.

I can get from the CFG the blocks and check blocks. And better, I can try detect common subsets for each block. With this approach I believe that I can write a more complete analysis and detect the code duplication better and in a easier way.

Challenges or Problems.

Yes, a lot ! For the first, I have decide use the Cecil.FlowAnalysis assembly (placed in the cecil module in mono svn) for obtain the CFG, I will save a lot of work using this library. But I have a little trouble.

Yesterday afternoon, I started working on the CFG analysis, then I started building the graphs; and I get a surprise:

1) Test.Rules.Smells.DetectCodeDuplicatedInSameClassTest.TestClassWithCodeDuplicated : System.ArgumentException : Exception handlers are not supported.
Parameter name: body
  at Cecil.FlowAnalysis.Impl.ControlFlow.FlowGraphBuilder..ctor (Mono.Cecil.MethodDefinition method) [0x00000] 
  at Cecil.FlowAnalysis.FlowGraphFactory.CreateControlFlowGraph (Mono.Cecil.MethodDefinition method) [0x00000] 
  at Gendarme.Rules.Smells.DetectCodeDuplicatedInSameClassRule.ContainsDuplicatedCode (Mono.Cecil.MethodDefinition currentMethod, Mono.Cecil.MethodDefinition targetMethod) [0x00000] 
  at Gendarme.Rules.Smells.DetectCodeDuplicatedInSameClassRule.CheckType (Mono.Cecil.TypeDefinition typeDefinition, Gendarme.Framework.Runner runner) [0x00000] 
  at Test.Rules.Smells.DetectCodeDuplicatedInSameClassTest.TestClassWithCodeDuplicated () [0x00000] 
  at &lt;0x00000> <unknown method>
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (object,object[])
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  </unknown>

Ouch ! Then I believe that I have to write a patch for allow exception handlers and build the graph.

Interesting resources.

This week, I only have an interesting resource that hope helps me with this work, the dragon's book :)

Finally thanks to Sebastien for solve my doubts. Also thanks to all mono people, every day I enjoy a bit more working with this great people.

I want also congratulate the Moonlight accomplishmet, I want try this technology!

Néstor Salceda