Building a code analyzer using Roslyn

We as developers rely a lot on the IDE features, such as IntelliSense, and other intelligent tooling to increase code quality and facilitate refactoring. But have you wondered what it would take to build your own code-aware tool? With Visual Studio 2015, we now have the ability to create custom code analyzers that provide real time code warnings and fixes. We can use them to enforce coding standards or to guide developers in avoiding common pitfalls. Let’s explore together how to build a code-aware library using the .NET Compiler Platform (Roslyn).

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2. Building a code analyzer using Roslyn Mihaela Diaconu
3. How has your IDE helped you lately?
4. Live code warnings
5. Live code warnings
6. Live code warnings
7. Live code fixes
8. Live code warnings
9. Project Roslyn • .NET Compiler Platform • C# compiler • VB compiler • Provides a set of APIs over the compiler
10. The compiler API
11. .NET Analyzers • Built on the .NET Compiler Platform API • Used to enforce best practices • May include code fixes • Distributed via NuGet or VSIX • NuGet Analyzers integrate with source control and build servers
12. Getting started • Visual Studio 2015 Community or Enterprise edition • .NET Compiler Platform SDK • Project template: • Analyzer with Code Fix (NuGet + VSIX)
13. Let’s find a problem to fix
14. Let’s find a problem to fix Log.Debug("Entry number: " + i + " is " + entry[i]);
15. Could logging have an impact on performance?
16. Could logging have an impact on performance? What if the logging level is turned off?
17. Could logging have an impact on performance? • Converting both integer i and entry[i] to strings • Strings concatenation Log.Debug("Entry number: " + i + " is " + entry[i]);
18. Solution if (log.IsDebugEnabled) { log.Debug("This is a complicated message."); }
19. Syntax tree
20. Syntax tree if (log.IsDebugEnabled)
21. Syntax tree if (log.IsDebugEnabled) { log.Debug("This is a complicated message."); }
22. .NET Analyzer [DiagnosticAnalyzer(LanguageNames.CSharp)] public class LogLevelAnalyzer : DiagnosticAnalyzer { ………… public override void Initialize(AnalysisContext context) { context.RegisterSyntaxNodeAction(AnalyzeNode, SyntaxKind.InvocationExpression); } }
23. .NET Analyzer [DiagnosticAnalyzer(LanguageNames.CSharp)] public class LogLevelAnalyzer : DiagnosticAnalyzer { ………… public override void Initialize(AnalysisContext context) { context.RegisterSyntaxNodeAction(AnalyzeNode, SyntaxKind.InvocationExpression); } }
24. .NET Analyzer [DiagnosticAnalyzer(LanguageNames.CSharp)] public class LogLevelAnalyzer : DiagnosticAnalyzer { ………… public override void Initialize(AnalysisContext context) { context.RegisterSyntaxNodeAction(AnalyzeNode, SyntaxKind.InvocationExpression); } }
25. .NET Analyzer [DiagnosticAnalyzer(LanguageNames.CSharp)] public class LogLevelAnalyzer : DiagnosticAnalyzer { ………… public override void Initialize(AnalysisContext context) { context.RegisterSyntaxNodeAction(AnalyzeNode, SyntaxKind.InvocationExpression); } }
26. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { var methodName = context.Node.Expression; if (!methodName.Name.ToString().StartsWith("Debug")) return; ………… } 1. Search for calls to “Debug” methods
27. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { var methodName = context.Node.Expression; if (!methodName.Name.ToString().StartsWith("Debug")) return; ………… }
28. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { ……… var namespace = context.SemanticModel.GetSymbolInfo(methodName).Symbol; if(!namespace.ToString().StartsWith("log4net.ILog")) return; ……… } 2. Is it the log4net “Debug”
29. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { ……… var namespace = context.SemanticModel.GetSymbolInfo(methodName).Symbol; if(!namespace.ToString().StartsWith("log4net.ILog")) return; ……… }
30. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { …………… var ancestors = methodName.Ancestors() .Where(node => node.Kind() == SyntaxKind.IfStatement); …………… } 3. Is the call enclosed in a IF
31. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { …………… var ancestors = methodName.Ancestors() .Where(node => node.Kind() == SyntaxKind.IfStatement); …………… }
32. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { …………… context.ReportDiagnostic(myCoolRule); } 4. Inform the IDE
33. .NET Analyzer void AnalyzeNode(SyntaxNodeAnalysisContext context) { …………… context.ReportDiagnostic(myCoolRule); }
34. Debugging time!
35. Library + Analyzer/Fix = Code-Aware Library
36. Library + Analyzer/Fix = Code-Aware Library • You don’t need to be a compiler guru to build a code analyzer • You can build a custom tool that fits to your needs
37. It’s a brave new world • https://github.com/dotnet/roslyn • https://github.com/dotnet/roslyn-analyzers • https://github.com/dotnet/roslyn/tree/master/src/Samples/CSharp
38. Questions?
39. https://goo.gl/2kTIzU Room 4 Codecamp Feedback
40. Thank you!