.NET Quality - Quick Reference

When NOT to Use This Skill

• SonarQube setup - Use sonarqube skill

• Security scanning - Use dotnet-security skill

• Testing - Use .NET test skills

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: dotnet for comprehensive documentation.

Tool Overview

Tool Focus Installation

dotnet format Formatting + analyzers Built-in

Roslyn Analyzers Code analysis NuGet

StyleCop.Analyzers Style rules NuGet

Roslynator Refactoring NuGet

SonarAnalyzer.CSharp SonarQube rules NuGet

Roslyn Analyzers Setup

Install Analyzers

<!-- Directory.Build.props (solution-wide) --> <Project> <PropertyGroup> <AnalysisLevel>latest-all</AnalysisLevel> <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild> <TreatWarningsAsErrors>true</TreatWarningsAsErrors> </PropertyGroup>

<ItemGroup> <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="8.0.0"> <PrivateAssets>all</PrivateAssets> <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets> </PackageReference> <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556"> <PrivateAssets>all</PrivateAssets> <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets> </PackageReference> <PackageReference Include="Roslynator.Analyzers" Version="4.10.0"> <PrivateAssets>all</PrivateAssets> <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets> </PackageReference> </ItemGroup> </Project>

.editorconfig

.editorconfig

root = true

[*] indent_style = space indent_size = 4 end_of_line = lf charset = utf-8 trim_trailing_whitespace = true insert_final_newline = true

[*.cs]

Organize usings

dotnet_sort_system_directives_first = true dotnet_separate_import_directive_groups = false

this. qualification

dotnet_style_qualification_for_field = false:warning dotnet_style_qualification_for_property = false:warning dotnet_style_qualification_for_method = false:warning dotnet_style_qualification_for_event = false:warning

Language keywords vs BCL types

dotnet_style_predefined_type_for_locals_parameters_members = true:warning dotnet_style_predefined_type_for_member_access = true:warning

var preferences

csharp_style_var_for_built_in_types = true:suggestion csharp_style_var_when_type_is_apparent = true:suggestion csharp_style_var_elsewhere = true:suggestion

Expression-bodied members

csharp_style_expression_bodied_methods = when_on_single_line:suggestion csharp_style_expression_bodied_constructors = false:suggestion csharp_style_expression_bodied_properties = true:suggestion csharp_style_expression_bodied_accessors = true:suggestion csharp_style_expression_bodied_lambdas = true:suggestion

Pattern matching

csharp_style_pattern_matching_over_is_with_cast_check = true:warning csharp_style_pattern_matching_over_as_with_null_check = true:warning

Null checking

csharp_style_throw_expression = true:suggestion csharp_style_conditional_delegate_call = true:warning dotnet_style_coalesce_expression = true:warning dotnet_style_null_propagation = true:warning

Code style

csharp_prefer_braces = true:warning csharp_prefer_simple_using_statement = true:suggestion csharp_style_prefer_switch_expression = true:suggestion

Naming conventions

dotnet_naming_rule.interface_should_be_begins_with_i.severity = warning dotnet_naming_rule.interface_should_be_begins_with_i.symbols = interface dotnet_naming_rule.interface_should_be_begins_with_i.style = begins_with_i

dotnet_naming_symbols.interface.applicable_kinds = interface dotnet_naming_symbols.interface.applicable_accessibilities = public, internal, private, protected dotnet_naming_style.begins_with_i.required_prefix = I dotnet_naming_style.begins_with_i.capitalization = pascal_case

dotnet_naming_rule.private_field_should_be_camel_case_with_underscore.severity = warning dotnet_naming_rule.private_field_should_be_camel_case_with_underscore.symbols = private_field dotnet_naming_rule.private_field_should_be_camel_case_with_underscore.style = camel_case_underscore

dotnet_naming_symbols.private_field.applicable_kinds = field dotnet_naming_symbols.private_field.applicable_accessibilities = private dotnet_naming_style.camel_case_underscore.required_prefix = _ dotnet_naming_style.camel_case_underscore.capitalization = camel_case

Analyzer severity

dotnet_diagnostic.CA1062.severity = warning # Validate arguments dotnet_diagnostic.CA1307.severity = warning # Specify StringComparison dotnet_diagnostic.CA1310.severity = warning # Specify StringComparison for correctness dotnet_diagnostic.CA2007.severity = none # ConfigureAwait (not needed in ASP.NET Core) dotnet_diagnostic.IDE0058.severity = none # Expression value never used

StyleCop

dotnet_diagnostic.SA1101.severity = none # Prefix local calls with this dotnet_diagnostic.SA1309.severity = none # Field names must not begin with underscore dotnet_diagnostic.SA1600.severity = none # Elements should be documented dotnet_diagnostic.SA1633.severity = none # File should have header

dotnet format

Commands

Check formatting

dotnet format --verify-no-changes

Fix formatting

dotnet format

Specific project

dotnet format ./src/MyProject

Analyzers only

dotnet format analyzers

Style only

dotnet format style

Whitespace only

dotnet format whitespace

With severity

dotnet format --severity warn

Common Analyzer Warnings

CA1062 - Validate Arguments

// BAD - No null check public void Process(string input) { Console.WriteLine(input.Length); // CA1062 }

// GOOD - Null check public void Process(string input) { ArgumentNullException.ThrowIfNull(input); Console.WriteLine(input.Length); }

// GOOD - Nullable reference type public void Process(string? input) { if (input is null) return; Console.WriteLine(input.Length); }

CA1307/CA1310 - StringComparison

// BAD - Culture-dependent if (name.Equals("admin")) // CA1307

// GOOD - Explicit comparison if (name.Equals("admin", StringComparison.OrdinalIgnoreCase))

// GOOD - For user-facing if (name.Equals(otherName, StringComparison.CurrentCultureIgnoreCase))

CA2000 - Dispose Objects

// BAD - Not disposed public void Process() { var stream = new FileStream("file.txt", FileMode.Open); // CA2000 // forgot to dispose }

// GOOD - Using statement public void Process() { using var stream = new FileStream("file.txt", FileMode.Open); // automatically disposed }

IDE0090 - Use Target-typed new

// Before List<string> items = new List<string>();

// After List<string> items = new();

// Or with var var items = new List<string>();

Common Code Smells & Fixes

1. God Class

// BAD - Does too much public class OrderProcessor { public void CreateOrder() { ... } public void SendEmail() { ... } public void GeneratePdf() { ... } public void CalculateTax() { ... } }

// GOOD - Single responsibility public class OrderService { private readonly IEmailService _emailService; private readonly IPdfGenerator _pdfGenerator; private readonly ITaxCalculator _taxCalculator;

public OrderService(
    IEmailService emailService,
    IPdfGenerator pdfGenerator,
    ITaxCalculator taxCalculator)
{
    _emailService = emailService;
    _pdfGenerator = pdfGenerator;
    _taxCalculator = taxCalculator;
}

public async Task<Order> CreateOrderAsync(OrderRequest request)
{
    var order = BuildOrder(request);
    order.Tax = _taxCalculator.Calculate(order);
    return order;
}

}

2. Async/Await Pitfalls

// BAD - Blocking async public void Process() { var result = GetDataAsync().Result; // Deadlock risk! }

// BAD - Async void (except event handlers) public async void ProcessAsync() // Can't be awaited, exceptions lost { await DoWorkAsync(); }

// GOOD - Async all the way public async Task ProcessAsync() { var result = await GetDataAsync(); }

// GOOD - When truly fire-and-forget public void StartBackgroundWork() { _ = Task.Run(async () => { try { await DoWorkAsync(); } catch (Exception ex) { _logger.LogError(ex, "Background work failed"); } }); }

3. Nullable Reference Types

// Enable in .csproj // <Nullable>enable</Nullable>

// BAD - Ignoring nullability public string GetName(User user) { return user.Name; // Warning if Name is string? }

// GOOD - Handle null public string GetName(User user) { return user.Name ?? "Unknown"; }

// GOOD - Return nullable public string? GetName(User? user) { return user?.Name; }

4. Record Types for DTOs

// BAD - Mutable class with boilerplate public class UserDto { public int Id { get; set; } public string Name { get; set; } public string Email { get; set; }

// Equals, GetHashCode, ToString...

}

// GOOD - Immutable record public record UserDto(int Id, string Name, string Email);

// With validation public record UserDto { public int Id { get; init; } public string Name { get; init; } public string Email { get; init; }

public UserDto(int id, string name, string email)
{
    ArgumentException.ThrowIfNullOrWhiteSpace(name);
    ArgumentException.ThrowIfNullOrWhiteSpace(email);

    Id = id;
    Name = name;
    Email = email;
}

}

5. Pattern Matching

// BAD - Type checking with cast if (shape is Circle) { var circle = (Circle)shape; return circle.Radius * circle.Radius * Math.PI; }

// GOOD - Pattern matching if (shape is Circle circle) { return circle.Radius * circle.Radius * Math.PI; }

// GOOD - Switch expression return shape switch { Circle c => c.Radius * c.Radius * Math.PI, Rectangle r => r.Width * r.Height, _ => throw new ArgumentException("Unknown shape") };

Pre-commit Setup

.pre-commit-config.yaml

repos:

• repo: local hooks:

  • id: dotnet-format name: dotnet format entry: dotnet format --verify-no-changes language: system types: [c#] pass_filenames: false

  • id: dotnet-build name: dotnet build entry: dotnet build --no-restore -warnaserror language: system types: [c#] pass_filenames: false

Quality Metrics Targets

Metric Target Tool

Cyclomatic Complexity < 10 Roslynator

Method Lines < 50 StyleCop

Parameters < 5 CA1026

Test Coverage

80% coverlet

Maintainability Index

60 VS Metrics

CI/CD Integration

GitHub Actions

name: Quality on: [push, pull_request]

jobs: quality: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4

  - name: Setup .NET
    uses: actions/setup-dotnet@v4
    with:
      dotnet-version: '8.0.x'

  - name: Restore
    run: dotnet restore

  - name: Format check
    run: dotnet format --verify-no-changes

  - name: Build
    run: dotnet build --no-restore -warnaserror

  - name: Test
    run: dotnet test --no-build --collect:"XPlat Code Coverage"

  - name: Upload coverage
    uses: codecov/codecov-action@v4

VS Code / Rider Settings

// .vscode/settings.json { "omnisharp.enableEditorConfigSupport": true, "omnisharp.enableRoslynAnalyzers": true, "[csharp]": { "editor.defaultFormatter": "ms-dotnettools.csharp", "editor.formatOnSave": true } }

Anti-Patterns

Anti-Pattern Why It's Bad Correct Approach

.Result / .Wait()

Deadlock risk Use async/await

async void

Exceptions lost Use async Task

Ignoring CA warnings Real issues hidden Fix or suppress with reason

No nullable reference types NullReferenceException Enable <Nullable>enable</Nullable>

#pragma warning disable

Hides issues Fix or suppress specifically

Mutable DTOs Unexpected changes Use records or init-only

Quick Troubleshooting

Issue Likely Cause Solution

Analyzer not running Package not installed Add to .csproj

Too many warnings First-time enable Suppress and fix incrementally

Format changes on build Different settings Commit .editorconfig

Nullable warnings everywhere Legacy code Enable gradually per project

StyleCop conflicts Different conventions Configure in .editorconfig

Related Skills

• SonarQube

• Clean Code

• .NET Security