June 29, 2018

...Learn TDD with Codemanship

.NET Code Analysis using NDepend

It's been a while since I used it in anger, but I've been having fun this week reaquainting myself with NDepend, the .NET code analysis tool.

Those of us who are interested on automating code reviews for Continuous Inspection have a range of options for .NET - ranging from tools built on the .NET Cecil decompiler - e.g., FxCop - to compiler-integrated tools on the Roslyn platform.

Ou of all them, I find NDepend to be by far the most mature. It's code model is much more expressive and intuitive (oh, the hours I've spent trying to map IL op codes on to source code!), it integrates out of the box with a range of popular build and reporting tools like VSTS, TeamCity, Excel and SonarQube. And in general, I find I'm up and running with a suite of usable quality gates much, much faster.



Under the covers, I believe we're still in Cecil/IL territory, but all the hard work's been done for us.

Creating analysis projects in NDepend is pretty straightforward. You can either select a set of .NET assemblies to be analysed, or a Visual Studio project or solution. It's very backwards-compatible, working with solutions as far back as VS 2005 (which, for training purposes, I still use occasionally).



I let it have a crack at the files for the Codemanship refactoring workshop, which are deliberately riddled with tasty code smells. My goal was to see how easy it would be to use NDepend to automatically detect the smells.



It found all the solution's assemblies, and crunched through them - building a code model and generating a report - in about a minute. When it's done, it opens a dashboard view which summarises the results of the analysis.



There's a lot going on in NDepend's UI, and this would be a very long blog post if I explored it all. But my goal was to use NDepend to detect the code smells in these projects, so I've focused on the features I'd use to do that.

First of all, out of the box with the code rules that come with NDepend, it has not detected any of the smells I'm interested in. This is tyicaly of any code analysis tool: the rules are not your rules. They're someone else's interpretation of code quality. FxCop's developers, for example, evidently have a way higher tolerance for complexity than I do.

The value in these tools is not in what they do out of the box, but in what you can make them do with a bit of thought. And for .NET, NDepend excels at this.

In the dialog at the bottom of the NDepend window, we can explore the code rules that it comes with and see how they've been implemented using NDepend's code model and some LINQ.



I'm interested in methods with too many parameters, so I clicked on that rule to bring up its implementation.



I happen to think that 5 parameters is too many, so could easily change the threshold where this rule is triggered in the LINQ. When I did, the results list immediately updated, showing the methods in my solution that have too many parameters.



This matches my expectation, and the instant feedback is very useful when creating custom quality gates - really speeds up the learning process.

To view the offending code, I just had to double click on that method in the results list, and NDepend opened it in Visual Studio. (You can use NDepend from within Visual Studio, too, if you want a more seamless experience.)



The interactive and integrated nature of NDepend makes it a useful tool to have in code reviews. I've always found going through the code inspecting source files by eye looking for issues hard work and really rather time-consuming. Being able to search for them interatively like this can help a lot.

Of course, we don't just want to look for code smells in code reviews - that's closing the stable door after the horse has bolted a lot of the time. It's quite fashionable now for dev teams to include code reviews as part of their check-in process - the dreaded Pull Request. It makes sense, as a last line of defence, to try to prevent issus being checked into the code respository. What I'm seeing more and more, though, is that pull requests can become a bottleneck for the team. Like any manual testing, it slows us down and hampers Continuous Delivery.

The command-line version of NDepend can easily be integrated into your build pipeline, allowing for some pretty comprehensive code reviews that can be performed automatically (and therefore quickly, alleviating the bottleneck).

I decided to turn this code rule into a quality gate that coud be used in a build, and set a policy that it should fail the build if more than 5 examples of long parameter lists are found.



So, up and running with a simple quality gate in no time. But what about more complex code smells, like message chains and feature envy? In the next blog post I'll go deeper into NDepend's Code Query Language and explore the kinds of queries we can create with more thought.







Posted 2 weeks, 3 days ago on June 29, 2018