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MA0169 - Detect equality operators that should be replaced with Equals method
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‎README.md‎

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@@ -184,6 +184,7 @@ If you are already using other analyzers, you can check [which rules are duplica
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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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|[MA0169](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0169.md)|Design|Use Equals method instead of operator|⚠️|✔️|❌|
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<!-- rules -->
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‎docs/README.md‎

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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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|[MA0169](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0169.md)|Design|Use Equals method instead of operator|<span title='Warning'>⚠️</span>|✔️|❌|
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|Id|Suppressed rule|Justification|
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|--|---------------|-------------|
@@ -680,6 +681,9 @@ 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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# MA0169: Use Equals method instead of operator
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dotnet_diagnostic.MA0169.severity = warning
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```
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# .editorconfig - all rules disabled
@@ -1185,4 +1189,7 @@ 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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# MA0169: Use Equals method instead of operator
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dotnet_diagnostic.MA0169.severity = none
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```

‎docs/Rules/MA0169.md‎

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# MA0169 - Use Equals method instead of operator
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Using `==` or `!=` operator on a type that overrides `Equals` method, but not the operators, is not recommended.
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````c#
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Sample a = default;
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Sample b = default;
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_ = a == b; // ok as Equals is not overrided
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class Sample { }
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````
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````c#
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Sample a = default;
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Sample b = default;
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_ = a == b; // ok the equality operator are defined
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class Sample
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{
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public static bool operator ==(Sample a, Sample b) => true;
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public static bool operator !=(Sample a, Sample b) => false;
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public override bool Equals(object obj) => true;
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public override int GetHashCode() => 0;
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}
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````
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````c#
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Sample a = default;
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Sample b = default;
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_ = a.Equals(b); // ok
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_ = object.Reference`Equals(a, b); // ok
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_ = a == b; // non-compliant
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class Sample
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{
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public override bool Equals(object obj) => true;
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public override int GetHashCode() => 0;
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}
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````
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‎src/Meziantou.Analyzer.Pack/configuration/default.editorconfig‎

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@@ -502,3 +502,6 @@ 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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# MA0169: Use Equals method instead of operator
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dotnet_diagnostic.MA0169.severity = warning

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

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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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# MA0169: Use Equals method instead of operator
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dotnet_diagnostic.MA0169.severity = none

‎src/Meziantou.Analyzer/Internals/MethodSymbolExtensions.cs‎

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using System.Linq;
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using System.Linq;
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using Microsoft.CodeAnalysis;
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namespace Meziantou.Analyzer.Internals;
@@ -56,6 +56,41 @@ private static bool IsInterfaceImplementation(this ISymbol symbol)
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.FirstOrDefault(interfaceMember => SymbolEqualityComparer.Default.Equals(symbol, symbol.ContainingType.FindImplementationForInterfaceMember(interfaceMember)));
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}
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public static bool IsOrOverrideMethod(this IMethodSymbol? symbol, IMethodSymbol? baseMethod)
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{
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if (symbol is null || baseMethod is null)
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return false;
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if (symbol.IsEqualTo(baseMethod))
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return true;
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while (symbol is not null)
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{
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if (symbol.IsEqualTo(baseMethod))
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return true;
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symbol = symbol.OverriddenMethod!;
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}
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return false;
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}
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public static bool OverrideMethod(this IMethodSymbol? symbol, IMethodSymbol? baseMethod)
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{
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if (symbol is null || baseMethod is null)
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return false;
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while (symbol.OverriddenMethod is not null)
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{
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if (symbol.OverriddenMethod.IsEqualTo(baseMethod))
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return true;
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symbol = symbol.OverriddenMethod!;
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}
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return false;
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}
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public static bool IsUnitTestMethod(this IMethodSymbol methodSymbol)
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{
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var attributes = methodSymbol.GetAttributes();

‎src/Meziantou.Analyzer/RuleIdentifiers.cs‎

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@@ -171,6 +171,7 @@ internal static class RuleIdentifiers
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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 const string UseEqualsMethodInsteadOfOperator = "MA0169";
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public static string GetHelpUri(string identifier)
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{

‎src/Meziantou.Analyzer/Rules/UseEqualsMethodInsteadOfOperatorAnalyzer.cs‎

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using System.Collections.Immutable;
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using System.Linq;
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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 UseEqualsMethodInsteadOfOperatorAnalyzer : DiagnosticAnalyzer
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{
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private static readonly DiagnosticDescriptor Rule = new(
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RuleIdentifiers.UseEqualsMethodInsteadOfOperator,
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title: "Use Equals method instead of operator",
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messageFormat: "Use Equals method instead of == or != operator",
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RuleCategories.Design,
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DiagnosticSeverity.Warning,
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isEnabledByDefault: true,
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description: "",
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helpLinkUri: RuleIdentifiers.GetHelpUri(RuleIdentifiers.UseEqualsMethodInsteadOfOperator));
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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.RegisterCompilationStartAction(context =>
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{
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if (context.Compilation.GetSpecialType(SpecialType.System_Object).GetMembers("Equals").FirstOrDefault() is not IMethodSymbol objectEqualsSymbol)
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return;
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context.RegisterOperationAction(context => AnalyzerBinaryOperation(context, objectEqualsSymbol), OperationKind.Binary);
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});
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}
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private static void AnalyzerBinaryOperation(OperationAnalysisContext context, IMethodSymbol objectEqualsSymbol)
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{
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var operation = (IBinaryOperation)context.Operation;
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if (operation is { OperatorKind: BinaryOperatorKind.Equals or BinaryOperatorKind.NotEquals, OperatorMethod: null })
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{
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if (IsNull(operation.LeftOperand) || IsNull(operation.RightOperand))
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return;
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var leftType = operation.LeftOperand.UnwrapImplicitConversionOperations().Type;
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if (operation.IsLifted)
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{
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leftType = leftType.GetUnderlyingNullableTypeOrSelf();
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}
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if (leftType is null)
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return;
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if (leftType.IsValueType)
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return;
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switch (leftType.SpecialType)
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{
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case SpecialType.System_Boolean:
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case SpecialType.System_Char:
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case SpecialType.System_DateTime:
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case SpecialType.System_SByte:
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case SpecialType.System_Int16:
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case SpecialType.System_Int32:
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case SpecialType.System_Int64:
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case SpecialType.System_IntPtr:
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case SpecialType.System_Byte:
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case SpecialType.System_UInt16:
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case SpecialType.System_UInt32:
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case SpecialType.System_UInt64:
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case SpecialType.System_UIntPtr:
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case SpecialType.System_Single:
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case SpecialType.System_Double:
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case SpecialType.System_Decimal:
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case SpecialType.System_Enum:
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case SpecialType.System_Object:
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case SpecialType.System_String:
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return;
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}
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// Check if the type have an Equals method
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var overrideEqualsSymbol = leftType.GetMembers("Equals").OfType<IMethodSymbol>().FirstOrDefault(m => m.IsOrOverrideMethod(objectEqualsSymbol));
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if (overrideEqualsSymbol is not null)
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{
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context.ReportDiagnostic(Rule, operation);
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}
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}
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}
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public static bool IsNull(IOperation operation)
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=> operation.UnwrapConversionOperations() is ILiteralOperation { ConstantValue: { HasValue: true, Value: null } };
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}

‎tests/Meziantou.Analyzer.Test/Rules/UseEqualsMethodInsteadOfOperatorAnalyzerTests.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 UseEqualsMethodInsteadOfOperatorAnalyzerTests
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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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.WithTargetFramework(Helpers.TargetFramework.Net9_0)
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.WithOutputKind(Microsoft.CodeAnalysis.OutputKind.ConsoleApplication)
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.WithAnalyzer<UseEqualsMethodInsteadOfOperatorAnalyzer>();
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}
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[Theory]
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[InlineData("System.Net.IPAddress")]
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public async Task Report_EqualsOperator(string type)
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{
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await CreateProjectBuilder()
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.WithSourceCode($$"""
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{{type}} a = null;
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{{type}} b = null;
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_ = [|a == b|];
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""")
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.ValidateAsync();
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}
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[Theory]
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[InlineData("char")]
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[InlineData("string")]
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[InlineData("sbyte")]
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[InlineData("byte")]
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[InlineData("short")]
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[InlineData("ushort")]
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[InlineData("int")]
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[InlineData("uint")]
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[InlineData("long")]
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[InlineData("ulong")]
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[InlineData("System.Int128")]
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[InlineData("System.UInt128")]
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[InlineData("System.Half")]
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[InlineData("float")]
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[InlineData("double")]
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[InlineData("decimal")]
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[InlineData("System.DayOfWeek")]
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public async Task NoReport_EqualsOperator(string type)
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{
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await CreateProjectBuilder()
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.WithSourceCode($$"""
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{{type}} a = default;
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{{type}} b = default;
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_ = a == b;
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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 ClassWithoutEqualsMethod()
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{
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await CreateProjectBuilder()
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.WithSourceCode($$"""
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Sample a = default;
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Sample b = default;
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_ = a == b;
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class Sample {}
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""")
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.ValidateAsync();
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}
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[Fact]
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public async Task RecordWithoutEqualsMethod()
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{
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await CreateProjectBuilder()
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.WithSourceCode($$"""
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Sample a = default;
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Sample b = default;
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_ = a == b; // Operator is implemented by the record
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record Sample {}
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""")
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.ValidateAsync();
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}
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}

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