Code Analysis — Roslyn Analyzers & EditorConfig

Core Principles

• Roslyn analyzers catch issues at compile time
• .editorconfig enforces consistent code style across the team
• Directory.Build.props enables analyzers for all projects
• TreatWarningsAsErrors in CI prevents degradation
• StyleCop.Analyzers for naming and formatting rules
• EnforceCodeStyleInBuild enables style warnings during build

Key Patterns

EditorConfig

# .editorconfig (solution root)
root = true

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

[*.cs]
# Namespace
csharp_style_namespace_declarations = file_scoped:warning

# Using directives
dotnet_sort_system_directives_first = true
csharp_using_directive_placement = outside_namespace: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_properties = true:suggestion

# Null checking
dotnet_style_prefer_is_null_check_over_reference_equality_method = true:warning

# Naming conventions
dotnet_naming_rule.private_fields.symbols = private_fields
dotnet_naming_rule.private_fields.style = _camelCase
dotnet_naming_rule.private_fields.severity = warning

dotnet_naming_symbols.private_fields.applicable_kinds = field
dotnet_naming_symbols.private_fields.applicable_accessibilities = private

dotnet_naming_style._camelCase.required_prefix = _
dotnet_naming_style._camelCase.capitalization = camel_case

# Analyzer severity
dotnet_diagnostic.CA1062.severity = warning  # Validate arguments
dotnet_diagnostic.CA1822.severity = suggestion  # Mark static
dotnet_diagnostic.CA2007.severity = none  # ConfigureAwait

Directory.Build.props Analyzer Configuration

<Project>
  <PropertyGroup>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
    <AnalysisLevel>latest-recommended</AnalysisLevel>
    <EnableNETAnalyzers>true</EnableNETAnalyzers>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
    <PackageReference Include="Meziantou.Analyzer" Version="2.0.182">
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
  </ItemGroup>
</Project>

StyleCop Configuration

// stylecop.json (solution root)
{
  "$schema": "https://raw.githubusercontent.com/DotNetAnalyzers/StyleCopAnalyzers/master/StyleCop.Analyzers/StyleCop.Analyzers/Settings/stylecop.schema.json",
  "settings": {
    "documentationRules": {
      "companyName": "{Company}",
      "xmlHeader": false,
      "documentInterfaces": false,
      "documentPrivateElements": false
    },
    "orderingRules": {
      "usingDirectivesPlacement": "outsideNamespace"
    }
  }
}

Suppressing False Positives

// Targeted suppression (prefer over global)
[SuppressMessage("Style", "IDE0057",
    Justification = "Range operator less readable here")]
public string GetPrefix(string value) => value.Substring(0, 3);

// Global suppression file
// GlobalSuppressions.cs
[assembly: SuppressMessage("Design", "CA1062",
    Scope = "namespaceanddescendants",
    Target = "~N:{Company}.{Domain}.Tests")]

Anti-Patterns

Anti-Pattern	Correct Approach
Disabling all warnings	Fix warnings or suppress with justification
No .editorconfig	Create one at solution root
Analyzers only in CI	Enable in IDE and build
Global suppressions without justification	Always include Justification

Detect Existing Patterns

# Find .editorconfig
find . -name ".editorconfig" -type f

# Find analyzer packages
grep -r "StyleCop\|Meziantou\|Roslynator" --include="*.csproj" .
grep -r "StyleCop\|Meziantou\|Roslynator" --include="*.props" .

# Find TreatWarningsAsErrors
grep -r "TreatWarningsAsErrors" --include="*.props" --include="*.csproj" .

Adding to Existing Project

1. Check for existing .editorconfig — extend, don't replace
2. Match existing analyzer configuration in Directory.Build.props
3. Don't enable TreatWarningsAsErrors without fixing existing warnings
4. Add analyzers gradually — start with recommended level
5. Run dotnet format to auto-fix formatting issues