Gendarme Tasks. Weekly Status Report #4

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 <0x00000>
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) [0×00000]


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!