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Add analyzer warning for duplicate enum case labels (NEEG003) (#162)
* Initial plan * Initial plan and exploration for duplicate case label analyzer Co-authored-by: andrewlock <18755388+andrewlock@users.noreply.github.com> * Add DuplicateEnumValueAnalyzer with comprehensive tests Co-authored-by: andrewlock <18755388+andrewlock@users.noreply.github.com> * Add final test case and complete DuplicateEnumValueAnalyzer implementation Co-authored-by: andrewlock <18755388+andrewlock@users.noreply.github.com> * Revert tfm * Tweak and update * Improve analyzer and update --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: andrewlock <18755388+andrewlock@users.noreply.github.com> Co-authored-by: Andrew Lock <andrewlock.net@gmail.com>
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‎src/NetEscapades.EnumGenerators/Diagnostics/DuplicateEnumValueAnalyzer.cs‎

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using System.Collections.Immutable;
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using System.Linq;
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using Microsoft.CodeAnalysis;
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using Microsoft.CodeAnalysis.CSharp;
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using Microsoft.CodeAnalysis.CSharp.Syntax;
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using Microsoft.CodeAnalysis.Diagnostics;
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namespace NetEscapades.EnumGenerators.Diagnostics;
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[DiagnosticAnalyzer(LanguageNames.CSharp)]
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public class DuplicateEnumValueAnalyzer : DiagnosticAnalyzer
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{
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public const string DiagnosticId = "NEEG003";
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public static readonly DiagnosticDescriptor Rule = new(
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#pragma warning disable RS2008 // Enable Analyzer Release Tracking
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id: DiagnosticId,
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#pragma warning restore RS2008
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title: "Enum has duplicate values and will give inconsistent values for ToStringFast()",
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messageFormat: "The enum member '{0}' has the same value as a previous member so will return the '{1}' value for ToStringFast()",
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category: "Usage",
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defaultSeverity: DiagnosticSeverity.Info,
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isEnabledByDefault: true);
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public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics
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=> ImmutableArray.Create(Rule);
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public override void Initialize(AnalysisContext context)
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{
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context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
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context.EnableConcurrentExecution();
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context.RegisterSyntaxNodeAction(AnalyzeEnumDeclaration, SyntaxKind.EnumDeclaration);
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}
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private static void AnalyzeEnumDeclaration(SyntaxNodeAnalysisContext context)
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{
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var enumDeclaration = (EnumDeclarationSyntax)context.Node;
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// Check if enum has [EnumExtensions] attribute
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bool hasEnumExtensionsAttribute = false;
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foreach (var attributeList in enumDeclaration.AttributeLists)
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{
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foreach (var attribute in attributeList.Attributes)
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{
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// Check attribute name syntactically first
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var attributeName = attribute.Name.ToString();
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if (attributeName == "EnumExtensions" || attributeName == "EnumExtensionsAttribute")
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{
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// Verify with semantic model for precision
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var symbolInfo = context.SemanticModel.GetSymbolInfo(attribute);
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if (symbolInfo.Symbol is IMethodSymbol method &&
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method.ContainingType.ToDisplayString() == Attributes.EnumExtensionsAttribute)
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{
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hasEnumExtensionsAttribute = true;
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break;
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}
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}
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}
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if (hasEnumExtensionsAttribute)
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{
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break;
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}
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}
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if (!hasEnumExtensionsAttribute)
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{
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return;
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}
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// Get the enum symbol
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var enumSymbol = context.SemanticModel.GetDeclaredSymbol(enumDeclaration);
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if (enumSymbol is null)
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{
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return;
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}
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// Track which constant values we've seen and the first name
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var seenValues = new Dictionary<object, string>();
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// Analyze each enum member
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foreach (var member in enumSymbol.GetMembers().OfType<IFieldSymbol>())
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{
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if (!member.IsConst || member.ConstantValue is null)
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{
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continue;
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}
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var constantValue = member.ConstantValue;
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var memberName = member.Name;
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// If we've already seen this value, this member will be excluded
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if (seenValues.TryGetValue(constantValue, out var previousName))
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{
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// Find the syntax location for this member
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var memberLocation = member.Locations.FirstOrDefault();
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if (memberLocation is not null)
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{
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var diagnostic = Diagnostic.Create(
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Rule,
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memberLocation,
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memberName,
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previousName);
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context.ReportDiagnostic(diagnostic);
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}
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}
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else
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{
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seenValues[member.ConstantValue] = memberName;
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}
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}
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}
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}

‎tests/NetEscapades.EnumGenerators.Tests/DuplicateEnumValueAnalyzerTests.cs‎

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using System.Diagnostics.CodeAnalysis;
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using System.Threading.Tasks;
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using NetEscapades.EnumGenerators.Diagnostics;
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using Xunit;
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using Verifier = Microsoft.CodeAnalysis.CSharp.Testing.CSharpAnalyzerVerifier<
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NetEscapades.EnumGenerators.Diagnostics.DuplicateEnumValueAnalyzer,
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Microsoft.CodeAnalysis.Testing.DefaultVerifier>;
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namespace NetEscapades.EnumGenerators.Tests;
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public class DuplicateEnumValueAnalyzerTests
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{
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private const string DiagnosticId = DuplicateEnumValueAnalyzer.DiagnosticId;
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[Fact]
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public async Task EmptySourceShouldNotHaveDiagnostics()
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{
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var test = string.Empty;
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task EnumWithoutAttributeShouldNotHaveDiagnostics()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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public enum TestEnum
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{
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First = 0,
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Second = 0,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task EnumWithoutDuplicatesShouldNotHaveDiagnostics()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum TestEnum
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{
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First = 0,
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Second = 1,
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Third = 2,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task EnumWithDuplicateValuesShouldHaveDiagnosticsForSecondOccurrence()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum TestEnum
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{
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First = 0,
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{|NEEG003:Second|} = 0,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task EnumWithMultipleDuplicateValuesShouldHaveDiagnosticsForAllButFirst()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum TestEnum
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{
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First = 0,
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{|NEEG003:Second|} = 0,
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{|NEEG003:Third|} = 0,
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Fourth = 1,
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{|NEEG003:Fifth|} = 1,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task EnumWithImplicitValuesShouldDetectDuplicates()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum TestEnum
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{
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First, // 0
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{|NEEG003:Second|} = 0, // duplicate of First
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{|NEEG003:Third|} = 0, // duplicate of First and Second
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task EnumWithDifferentTypesButSameValuesShouldDetectDuplicates()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum TestEnum : byte
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{
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First = 0,
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{|NEEG003:Second|} = 0,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task MultipleEnumsWithDuplicatesShouldTrackSeparately()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum FirstEnum
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{
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A = 0,
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{|NEEG003:B|} = 0,
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}
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[EnumExtensions]
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public enum SecondEnum
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{
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X = 0,
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{|NEEG003:Y|} = 0,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task ComplexEnumThatReferencesOthers()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum ComplexEnum
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{
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Zero = 0,
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One = 1,
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{|NEEG003:AlsoOne|} = One,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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[Fact]
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public async Task ComplexEnumThatReferencesCombinationOfOthers()
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{
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var test = GetTestCode(
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/* lang=c# */
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"""
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[EnumExtensions]
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public enum ComplexEnum
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{
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Zero = 0,
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One = 1,
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Two = 2,
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{|NEEG003:ZeroAndOne|} = Zero | One,
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OneAndTwo = One | Two,
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}
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""");
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await Verifier.VerifyAnalyzerAsync(test);
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}
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private static string GetTestCode(string testCode) => $$"""
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using System.Threading;
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using System.Threading.Tasks;
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using System.Diagnostics;
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using NetEscapades.EnumGenerators;
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namespace ConsoleApplication1
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{
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{{testCode}}
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}
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{{TestHelpers.LoadEmbeddedAttribute()}}
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""";
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}

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