Automating C# Coding Standards using StyleCop and FxCop

James Hare – Application Architect, Scottrade

What are Coding Standards?
A set of rules or guidelines used when writing the source code of a computer program.
Generally dictates:
Safety mandates to avoid introducing errors.
Style mandates to increase maintainability.
Security mandates to avoid vulnerabilities.
Efficiency mandates to help increase performance.
Standards may be enforced through code reviews or may simply be “suggestions”.

Standards: Like or Dislike?

But, Isn’t Programming Art?
This always has been an interesting point of contention.
On one extreme development can be thought of as a work of art and any source that reaches a logically correct result is acceptable and everything else is just “style.”
The other extreme believes that programming is purely a mechanical process and there is only a limited number of correct answers.
Which is correct?

Reality Lies In Between
It may be more accurate to say developers are more like artisans (crafters) than artists, though containing elements of both.
An artist has a wide range of forms they can adhere to and much is dependent on the interpretation of the viewer.
In contrast, artisans tend to construct or design for a purpose, and while there are some elements of style in construction, if it fails to achieve its purpose effectively , it is a failure.

The “Art” of Sorting
Take sorting, for example.
Both Bubble sort and Quick sort are valid sorts on a set of data.
Bubble sort has a complexity of O(n 2 ) and Quick sort is O(n log n).
Assuming sorting 1 million elements and each check takes 1 µs, roughly this would be:
Bubble Sort: 11 days
Quick Sort: 19 seconds
Both sort data, but one is clearly more useful.

Standardizing an “Art”
While there are many ways to solve a given problem, there should be guidelines for effective construction.
These guidelines are similar to building codes used in building construction to ensure safety and quality.
These guidelines form the basis for coding standards and are best compiled from group consensus and industry best practices.

Enforcing Standards
Standards should be enforced to promote safety, efficiency, and maintainability.
Standards can be enforced through Code Reviews, but these tend to be applied with varying levels of adherence.
It’s much better to attempt to automate as much of your standards as possible so that the code is judged more objectively.

Benefits of Automation
Standards are applied objectively since only analyzes the source or assembly.
Just plain faster than trying to catch standards violations manually.
Code authors don’t feel personally attacked.
Frees more reviewer time since won’t have to waste as much time in code reviews.
Frees more time for developers since code spends less time and iterations in review.

Standards Automation Tools
There are two primary tools from Microsoft:
StyleCop – Analyzes source files to determine if source code is correctly formatted.
FxCop (Static Code Analysis) – Analyzes assemblies to determine if code is constructed safely and optimally.
These tools overlap in some of their base rules but both have their strengths.
Other third party and Microsoft tools exist, but beyond this presentation’s scope.

StyleCop
Analyzes source files and not compiled code.
Great for checking elements such as:
Spacing
Comments
File composition
Naming
Cannot easily check type hierarchies or program structure.
Available at http://stylecop.codeplex.com/

Configuring StyleCop
If you have StyleCop installed, you can have Settings.StyleCop files for each project if you want to vary styles per project.
Will take the first Settings.StyleCop file it finds from working directory on up the path.
Default will be the Settings.StyleCop file in c:program filesMicrosoft StyleCop…
Various configurations can make harder to enforce uniform rules, though, so use with caution.

You can configure which base rules you want active by using StyleCopSettingsEditor.exe.
Let’s take a minute to look at the rules…

You can also get to StyleCop settings in Visual Studio directly by right-clicking a project.
This creates local copy of rules, use cautiously.

Running StyleCop
You can run StyleCop from VS or MSBuild.
Has no native command-line interface, but one exists at sourceforge called StyleCopCmd .

StyleCop Results
Shows in Error List window, can turn on “Warnings as Errors” in VS if you want to break builds on violations.

Suppressing a Rule
Most rules are good all the time, sometimes not.

On Suppressing Rules
It’s better to keep a rule even if it only applies 95% of the time and force developers to suppress the rule for the one-off exceptions.
This puts a SuppressMessage attribute in code which must be justified and prevents viewing the exception to the rule as a precedent for ignoring the rule.
If code reviewer disagrees, can be debated.
Turning off rules should be avoided unless the rule is invalid most or all of the time.

Custom StyleCop Rules
StyleCop rules are fairly easy to write.
Create class library that references the StyleCop assemblies:
Located in c:program filesMicrosoft StyleCop…
Microsoft.StyleCop.dll
Microsoft.StyleCop.Csharp.dll
Add a CS (C# source file) for new analyzer.
Add an XML file for rule configuration.

In the CS file, create an analyzer that inherits from SourceAnalyzer and has class attribute also named SourceAnalyzer for C# files.s

In the CS file, override AnalyzeDocument and perform your checks.

When you see your violation, call the method AddViolation and give it a rule name and args:

Custom Style Cop Rules
Then, in the XML file, define the rule and message. Make sure XML file has same name as class name and is Embedded Resource.

Then, build the custom assembly.
Place custom assembly in:
C:Program FilesMicrosoft StyleCop …
You should now see custom rules in the StyleCopSettingsEditor.
If you don’t see custom rules, check that the XML file:
Is an embedded resource
Has same filename as the class name (minus extensions)
Let’s look at the code more closely…

StyleCop for ReSharper
JetBrains’s ReSharper is an Visual Studio IDE plug-in that adds a lot of refactoring and aids.
StyleCop for ReSharper is a ReSharper plug-in that allows for dynamic checking of StyleCop rules as you type.
Will highlight rule violations with squiggle just like other ReSharper hints.
http://stylecopforresharper.codeplex.com/
Let’s look at how this appears in the IDE.

FxCop (aka VS Code Analysis)
Great for checking elements such as:
Non-spacing style issues (naming, etc).
Code safety and performance issues
Type hierarchy issues
Analysis of database objects
Cannot check source style such as spacing.
Already baked into Visual Studio 2008/10.
Can also be used as a stand-alone.

Running FxCop Stand-Alone
Start  Programs  Microsoft FxCop
Create new project, add targets, and Analyze!

Running FxCop From Visual Studio
Right click on project or solution and choose Run Code Analysis:
Let’s look at an example analysis.

Suppressing FxCop Errors
Just like in StyleCop, you can suppress one-off exceptions to the rules.
Can insert manually or automatically from the error list in Visual Studio.

Custom FxCop Rules
Create a Class Library in Visual Studio.
Add references to FxCop assemblies:
From C:Program FilesMicrosoft FxCop…
FxCopCommon.dll
FxCopSdk.dll
Microsoft.Cci.dll
Microsoft.VisualStudio.CodeAnalysis
Add a CS file for the new rule.
Add an XML file for the rule definition.

Custom FxCop Rules
In CS file create class that inherits from BaseIntrospectionRule :

Custom FxCop Rules
In CS File, override Check to check rule.

Custom FxCop Rule
XML file is Embedded and contains rule detail:
Remember filename must be same as passed to base constructor of BaseIntrospectionRule.

Custom FxCop Rules
To use custom rule, use CTRL+R or Project  Add Rules in FxCop.
You can verify by clicking on rules tab:

Summary
Automating code standards can be very useful for getting rid of a lot of the “noise” in code reviews and allowing reviewers to concentrate on logic bugs.
Automated code standards take the personal side out of enforcing style, safety, and performance.
Custom rules can be used in FxCop and StyleCop to allow for your own rules.

Questions?
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Automating C# Coding Standards using StyleCop and FxCop

by BlackRabbitCoder on Aug 24, 2010

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Automating C# Coding Standards using StyleCop and FxCop — Presentation Transcript