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Add rule to detect non-readonly struct used for in or ref readonly parameters
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‎README.md‎

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@@ -183,6 +183,7 @@ If you are already using other analyzers, you can check [which rules are duplica
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|[MA0165](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0165.md)|Usage|Make interpolated string|👻|✔️|✔️|
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|[MA0166](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0166.md)|Usage|Forward the TimeProvider to methods that take one|ℹ️|✔️|✔️|
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|[MA0167](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0167.md)|Usage|Use an overload with a TimeProvider argument|ℹ️|❌|❌|
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|[MA0168](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0168.md)|Performance|Use readonly struct for in or ref readonly parameter|ℹ️|❌|❌|
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<!-- rules -->
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‎docs/README.md‎

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|[MA0165](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0165.md)|Usage|Make interpolated string|<span title='Hidden'>👻</span>|✔️|✔️|
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|[MA0166](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0166.md)|Usage|Forward the TimeProvider to methods that take one|<span title='Info'>ℹ️</span>|✔️|✔️|
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|[MA0167](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0167.md)|Usage|Use an overload with a TimeProvider argument|<span title='Info'>ℹ️</span>|❌|❌|
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|[MA0168](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0168.md)|Performance|Use readonly struct for in or ref readonly parameter|<span title='Info'>ℹ️</span>|❌|❌|
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|Id|Suppressed rule|Justification|
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|--|---------------|-------------|
@@ -676,6 +677,9 @@ dotnet_diagnostic.MA0166.severity = suggestion
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# MA0167: Use an overload with a TimeProvider argument
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dotnet_diagnostic.MA0167.severity = none
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# MA0168: Use readonly struct for in or ref readonly parameter
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dotnet_diagnostic.MA0168.severity = none
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```
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# .editorconfig - all rules disabled
@@ -1178,4 +1182,7 @@ dotnet_diagnostic.MA0166.severity = none
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# MA0167: Use an overload with a TimeProvider argument
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dotnet_diagnostic.MA0167.severity = none
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# MA0168: Use readonly struct for in or ref readonly parameter
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dotnet_diagnostic.MA0168.severity = none
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```

‎docs/Rules/MA0168.md‎

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# MA0168 - Use readonly struct for in or ref readonly parameter
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```c#
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void A(in Foo p) { } // not-compliant as Foo is not readonly
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struct Foo { }
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```
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```c#
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void A(in Foo p) { } // ok
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readonly struct Foo { }
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```

‎src/Meziantou.Analyzer.Pack/configuration/default.editorconfig‎

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# MA0167: Use an overload with a TimeProvider argument
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dotnet_diagnostic.MA0167.severity = none
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# MA0168: Use readonly struct for in or ref readonly parameter
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dotnet_diagnostic.MA0168.severity = none

‎src/Meziantou.Analyzer.Pack/configuration/none.editorconfig‎

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@@ -499,3 +499,6 @@ dotnet_diagnostic.MA0166.severity = none
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# MA0167: Use an overload with a TimeProvider argument
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dotnet_diagnostic.MA0167.severity = none
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# MA0168: Use readonly struct for in or ref readonly parameter
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dotnet_diagnostic.MA0168.severity = none

‎src/Meziantou.Analyzer/RuleIdentifiers.cs‎

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@@ -170,6 +170,7 @@ internal static class RuleIdentifiers
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public const string MakeInterpolatedString = "MA0165";
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public const string UseAnOverloadThatHasTimeProviderWhenAvailable = "MA0166";
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public const string UseAnOverloadThatHasTimeProvider = "MA0167";
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public const string UseReadOnlyStructForRefReadOnlyParameters = "MA0168";
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public static string GetHelpUri(string identifier)
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{

‎src/Meziantou.Analyzer/Rules/UseReadOnlyStructForRefReadOnlyParametersAnalyzer.cs‎

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using System.Collections.Immutable;
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using Meziantou.Analyzer.Internals;
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using Microsoft.CodeAnalysis;
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using Microsoft.CodeAnalysis.Diagnostics;
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using Microsoft.CodeAnalysis.Operations;
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namespace Meziantou.Analyzer.Rules;
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[DiagnosticAnalyzer(LanguageNames.CSharp)]
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public sealed class UseReadOnlyStructForRefReadOnlyParametersAnalyzer : DiagnosticAnalyzer
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{
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private static readonly DiagnosticDescriptor Rule = new(
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RuleIdentifiers.UseReadOnlyStructForRefReadOnlyParameters,
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title: "Use readonly struct for in or ref readonly parameter",
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messageFormat: "Use readonly struct for in or ref readonly parameter",
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RuleCategories.Performance,
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DiagnosticSeverity.Info,
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isEnabledByDefault: false,
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description: "",
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helpLinkUri: RuleIdentifiers.GetHelpUri(RuleIdentifiers.UseReadOnlyStructForRefReadOnlyParameters));
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public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
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public override void Initialize(AnalysisContext context)
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{
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context.EnableConcurrentExecution();
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context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
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context.RegisterSymbolAction(context =>
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{
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var parameter = (IParameterSymbol)context.Symbol;
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if (!IsValidParameter(parameter))
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{
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context.ReportDiagnostic(Rule, parameter);
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}
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}, SymbolKind.Parameter);
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context.RegisterOperationAction(context =>
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{
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var operation = (ILocalFunctionOperation)context.Operation;
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var symbol = operation.Symbol;
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foreach (var parameter in symbol.Parameters)
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{
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if (!IsValidParameter(parameter))
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{
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context.ReportDiagnostic(Rule, parameter);
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}
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}
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}, OperationKind.LocalFunction);
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context.RegisterOperationAction(ctx =>
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{
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var operation = (IArgumentOperation)ctx.Operation;
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var parameter = operation.Parameter;
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if (parameter is null)
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return;
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// Do not report non-generic types as they are reported by SymbolAction
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if (SymbolEqualityComparer.Default.Equals(parameter.OriginalDefinition.Type, parameter.Type))
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return;
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if (!IsValidParameter(parameter))
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{
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ctx.ReportDiagnostic(Rule, operation);
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}
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}, OperationKind.Argument);
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}
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private static bool IsValidParameter(IParameterSymbol parameter)
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{
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if (parameter.RefKind is RefKind.In or RefKind.RefReadOnlyParameter)
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{
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if (parameter.Type is INamedTypeSymbol namedTypeSymbol)
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{
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if (namedTypeSymbol.IsValueType && !namedTypeSymbol.IsReadOnly)
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return false;
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}
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}
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return true;
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}
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}

‎tests/Meziantou.Analyzer.Test/Rules/UseReadOnlyStructForRefReadOnlyParametersAnalyzerTests.cs‎

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using System.Threading.Tasks;
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using Meziantou.Analyzer.Rules;
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using TestHelper;
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using Xunit;
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namespace Meziantou.Analyzer.Test.Rules;
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public class UseReadOnlyStructForRefReadOnlyParametersAnalyzerTests
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{
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private static ProjectBuilder CreateProjectBuilder()
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{
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return new ProjectBuilder()
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.WithOutputKind(Microsoft.CodeAnalysis.OutputKind.ConsoleApplication)
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.WithAnalyzer<UseReadOnlyStructForRefReadOnlyParametersAnalyzer>();
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}
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[Fact]
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public async Task ParameterNotRefReadOnly()
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{
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await CreateProjectBuilder()
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.WithSourceCode("""
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A(default);
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void A(Foo foo) { }
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struct Foo { }
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""")
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.ValidateAsync();
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}
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[Fact]
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public async Task StructNotReadOnly_in()
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{
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await CreateProjectBuilder()
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.WithSourceCode("""
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A(default);
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void A(in Foo [|foo|]) { }
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struct Foo { }
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""")
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.ValidateAsync();
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}
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[Fact]
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public async Task StructNotReadOnly_ref_readonly()
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{
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await CreateProjectBuilder()
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.WithSourceCode("""
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A(default);
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void A(ref readonly Foo [|foo|]) { }
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struct Foo { }
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""")
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.ValidateAsync();
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}
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[Fact]
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public async Task StructReadOnly()
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{
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await CreateProjectBuilder()
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.WithSourceCode("""
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A(default);
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void A(in Foo foo) { }
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readonly struct Foo { }
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""")
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.ValidateAsync();
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}
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[Fact]
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public async Task StructNotReadOnly_Generic()
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{
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await CreateProjectBuilder()
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.WithSourceCode("""
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A([|new Foo()|]);
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void A<T>(in T foo) where T: struct { }
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struct Foo { }
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""")
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.ValidateAsync();
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}
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[Fact]
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public async Task StructReadOnly_Generic()
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{
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await CreateProjectBuilder()
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.WithSourceCode("""
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A(new Foo());
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void A<T>(in T foo) where T: struct { }
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readonly struct Foo { }
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""")
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.ValidateAsync();
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}
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}

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