Use it or lose it, part deux [New Delay.FxCop code analysis rule helps identify uncalled public or private methods and properties in a .NET assembly]

Previous posts introduced the Delay.FxCop custom code analysis assembly and demonstrated the benefits of automated code analysis for easily identifying problem areas in an assembly. The Delay.FxCop project included two rules, DF1000: Check spelling of all string literals and DF1001: Resources should be referenced - today I'm introducing another! The new rule follows in the footsteps of DF1001 by identifying unused parts of an assembly that can be removed to save space and reduce complexity. But while DF1001 operated on resources, today's DF1002: Uncalled methods should be removed analyzes the methods and properties of an assembly to help find those stale bits of code that aren't being used any more.

    Note: If this functionality seems familiar, it's because CA1811: Avoid uncalled private code is one of the standard FxCop rules. I've always been a big fan of CA1811, but frequently wished it could look beyond just private code to consider all code. Of course, limiting the scope of the "in-box" rule makes perfect sense from an FxCop point of view: you don't want the default rules to be noisy or else they'll get turned off and ignored. But the Delay.FxCop assembly isn't subject to the same restrictions, so I thought it would be neat to experiment with an implementation that analyzed all of an assembly's code.

    Further note: One of the downsides of this increased scope is that DF1002 can't distinguish between methods that are part of a library's public API and those that are accidentally unused. As far as DF1002 is concerned, they're both examples of code that's not called from within the assembly. Therefore, running this rule on a library involves some extra overhead to suppress the warnings for public APIs. If it's just a little extra work, maybe it's still worthwhile - but if it's overwhelming, you can always disable DF1002 for library assemblies and restrict it to applications where it's more relevant.

 

Implementation-wise, DF1002: Uncalled methods should be removed isn't all that different from its predecessors - in fact, it extends and reuses the same assembly node enumeration helper introduced with DF1001. During analysis, every method of the assembly is visited and if it isn't "used" (more on this in a moment), a code analysis warning is output:

DF1002 : Performance : The method 'SilverlightApplication.MainPage.UnusedPublicMethod' does not appear to be used in code.

Of course, these warnings can be suppressed in the usual manner:

[assembly: SuppressMessage("Usage", "DF1001:ResourcesShouldBeReferenced",
           MessageId = "app.xaml", Scope = "resource", Target = "SilverlightApplication.g.resources",
           Justification = "Loaded by Silverlight for App.xaml.")]

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