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[EC82] Variable can be made constant (#21)
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| This project incorporates ideas and code from the following open-source projects, whose contribution to the open-source community is greatly appreciated: | ||
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| **Roslynator**: https://github.com/dotnet/roslynator. Copyright (c) .NET Foundation and Contributors. | ||
| Licensed under the Apache License, Version 2.0; full text can be found at https://www.apache.org/licenses/LICENSE-2.0. | ||
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| **Meziantou.Analyzer**: https://github.com/meziantou/Meziantou.Analyzer. Copyright (c) Gérald Barré. | ||
| Licensed under the MIT License; full text can be found at https://opensource.org/licenses/MIT. |
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81 changes: 81 additions & 0 deletions
81
src/EcoCode.Analyzers/Analyzers/EC82_VariableCanBeMadeConstantAnalyzer.cs
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| namespace EcoCode.Analyzers; | ||
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| /// <summary>Analyzer for variable can be made constant.</summary> | ||
| [DiagnosticAnalyzer(LanguageNames.CSharp)] | ||
| public sealed class VariableCanBeMadeConstantAnalyzer : DiagnosticAnalyzer | ||
| { | ||
| private static readonly ImmutableArray<SyntaxKind> SyntaxKinds = [SyntaxKind.LocalDeclarationStatement]; | ||
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| /// <summary>The diagnostic descriptor.</summary> | ||
| public static DiagnosticDescriptor Descriptor { get; } = new( | ||
| Rule.Ids.EC82_VariableCanBeMadeConstant, | ||
| title: "Variable can be made constant", | ||
| messageFormat: "Variable can be made constant", | ||
| Rule.Categories.Usage, | ||
| DiagnosticSeverity.Info, | ||
| isEnabledByDefault: true, | ||
| description: null, | ||
| helpLinkUri: Rule.GetHelpUri(Rule.Ids.EC82_VariableCanBeMadeConstant)); | ||
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| /// <inheritdoc/> | ||
| public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => [Descriptor]; | ||
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| /// <inheritdoc/> | ||
| public override void Initialize(AnalysisContext context) | ||
| { | ||
| context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None); | ||
| context.EnableConcurrentExecution(); | ||
| context.RegisterSyntaxNodeAction(static context => AnalyzeNode(context), SyntaxKinds); | ||
| } | ||
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| private static void AnalyzeNode(SyntaxNodeAnalysisContext context) | ||
| { | ||
| var localDeclaration = (LocalDeclarationStatementSyntax)context.Node; | ||
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| // Make sure the declaration isn't already const | ||
| if (localDeclaration.Modifiers.Any(SyntaxKind.ConstKeyword)) | ||
| return; | ||
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| // Ensure that all variables in the local declaration have initializers that are assigned with constant values | ||
| var variableType = context.SemanticModel.GetTypeInfo(localDeclaration.Declaration.Type, context.CancellationToken).ConvertedType; | ||
| if (variableType is null) return; | ||
| foreach (var variable in localDeclaration.Declaration.Variables) | ||
| { | ||
| var initializer = variable.Initializer; | ||
| if (initializer is null) return; | ||
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| var constantValue = context.SemanticModel.GetConstantValue(initializer.Value, context.CancellationToken); | ||
| if (!constantValue.HasValue) return; | ||
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| // Ensure that the initializer value can be converted to the type of the local declaration without a user-defined conversion. | ||
| var conversion = context.SemanticModel.ClassifyConversion(initializer.Value, variableType); | ||
| if (!conversion.Exists || conversion.IsUserDefined) return; | ||
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| // Special cases: | ||
| // * If the constant value is a string, the type of the local declaration must be string | ||
| // * If the constant value is null, the type of the local declaration must be a reference type | ||
| if (constantValue.Value is string) | ||
| { | ||
| if (variableType.SpecialType is not SpecialType.System_String) return; | ||
| } | ||
| else if (variableType.IsReferenceType && constantValue.Value is not null) | ||
| { | ||
| return; | ||
| } | ||
| } | ||
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| // Perform data flow analysis on the local declaration | ||
| var dataFlowAnalysis = context.SemanticModel.AnalyzeDataFlow(localDeclaration); | ||
| if (dataFlowAnalysis is null) return; | ||
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| foreach (var variable in localDeclaration.Declaration.Variables) | ||
| { | ||
| // Retrieve the local symbol for each variable in the local declaration and ensure that it is not written outside of the data flow analysis region | ||
| var variableSymbol = context.SemanticModel.GetDeclaredSymbol(variable, context.CancellationToken); | ||
| if (variableSymbol is null || dataFlowAnalysis.WrittenOutside.Contains(variableSymbol)) | ||
| return; | ||
| } | ||
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| context.ReportDiagnostic(Diagnostic.Create(Descriptor, context.Node.GetLocation())); | ||
| } | ||
| } |
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92 changes: 92 additions & 0 deletions
92
src/EcoCode.CodeFixes/CodeFixes/EC82_VariableCanBeMadeConstantCodeFixProvider.cs
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,92 @@ | ||
| using Microsoft.CodeAnalysis.CodeActions; | ||
| using Microsoft.CodeAnalysis.CSharp; | ||
| using Microsoft.CodeAnalysis.CSharp.Syntax; | ||
| using Microsoft.CodeAnalysis.Formatting; | ||
| using Microsoft.CodeAnalysis.Simplification; | ||
| using System.Threading; | ||
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| namespace EcoCode.CodeFixes; | ||
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| /// <summary>The code fix provider for variable can be made constant.</summary> | ||
| [ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(VariableCanBeMadeConstantCodeFixProvider)), Shared] | ||
| public sealed class VariableCanBeMadeConstantCodeFixProvider : CodeFixProvider | ||
| { | ||
| /// <inheritdoc/> | ||
| public override ImmutableArray<string> FixableDiagnosticIds => [VariableCanBeMadeConstantAnalyzer.Descriptor.Id]; | ||
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| /// <inheritdoc/> | ||
| public override FixAllProvider GetFixAllProvider() => WellKnownFixAllProviders.BatchFixer; | ||
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| /// <inheritdoc/> | ||
| public override async Task RegisterCodeFixesAsync(CodeFixContext context) | ||
| { | ||
| if (context.Diagnostics.Length == 0) return; | ||
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| var document = context.Document; | ||
| var root = await document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false); | ||
| if (root is null) return; | ||
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| var diagnostic = context.Diagnostics[0]; | ||
| var parent = root.FindToken(diagnostic.Location.SourceSpan.Start).Parent; | ||
| if (parent is null) return; | ||
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| foreach (var node in parent.AncestorsAndSelf()) | ||
| { | ||
| if (node is not LocalDeclarationStatementSyntax declaration) continue; | ||
| context.RegisterCodeFix( | ||
| CodeAction.Create( | ||
| title: "Make variable constant", | ||
| createChangedDocument: token => RefactorAsync(document, declaration, token), | ||
| equivalenceKey: "Make variable constant"), | ||
| diagnostic); | ||
| break; | ||
| } | ||
| } | ||
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| private static async Task<Document> RefactorAsync(Document document, LocalDeclarationStatementSyntax localDecl, CancellationToken token) | ||
| { | ||
| // Remove the leading trivia from the local declaration. | ||
| var firstToken = localDecl.GetFirstToken(); | ||
| var leadingTrivia = firstToken.LeadingTrivia; | ||
| var trimmedLocal = leadingTrivia.Any() | ||
| ? localDecl.ReplaceToken(firstToken, firstToken.WithLeadingTrivia(SyntaxTriviaList.Empty)) | ||
| : localDecl; | ||
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| // Create a const token with the leading trivia. | ||
| var constToken = SyntaxFactory.Token(leadingTrivia, SyntaxKind.ConstKeyword, SyntaxFactory.TriviaList(SyntaxFactory.ElasticMarker)); | ||
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| // If the type of the declaration is 'var', create a new type name for the inferred type. | ||
| var varDecl = localDecl.Declaration; | ||
| var varTypeName = varDecl.Type; | ||
| if (varTypeName.IsVar) | ||
| varDecl = await GetDeclarationForVarAsync(document, varDecl, varTypeName, token).ConfigureAwait(false); | ||
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| // Produce the new local declaration with an annotation | ||
| var formattedLocal = trimmedLocal | ||
| .WithModifiers(trimmedLocal.Modifiers.Insert(0, constToken)) // Insert the const token into the modifiers list | ||
| .WithDeclaration(varDecl) | ||
| .WithAdditionalAnnotations(Formatter.Annotation); | ||
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| // Replace the old local declaration with the new local declaration. | ||
| var oldRoot = await document.GetSyntaxRootAsync(token).ConfigureAwait(false); | ||
| return oldRoot is null ? document : document.WithSyntaxRoot(oldRoot.ReplaceNode(localDecl, formattedLocal)); | ||
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| static async Task<VariableDeclarationSyntax> GetDeclarationForVarAsync(Document document, VariableDeclarationSyntax varDecl, TypeSyntax varTypeName, CancellationToken token) | ||
| { | ||
| var semanticModel = await document.GetSemanticModelAsync(token).ConfigureAwait(false); | ||
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| if (semanticModel is null || semanticModel.GetAliasInfo(varTypeName, token) is not null) | ||
| return varDecl; // Special case: Ensure that 'var' isn't actually an alias to another type (e.g. using var = System.String) | ||
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| var type = semanticModel.GetTypeInfo(varTypeName, token).ConvertedType; | ||
| if (type is null || type.Name == "var") return varDecl; // Special case: Ensure that 'var' isn't actually a type named 'var' | ||
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| // Create a new TypeSyntax for the inferred type. Be careful to keep any leading and trailing trivia from the var keyword. | ||
| return varDecl.WithType(SyntaxFactory | ||
| .ParseTypeName(type.ToDisplayString()) | ||
| .WithLeadingTrivia(varTypeName.GetLeadingTrivia()) | ||
| .WithTrailingTrivia(varTypeName.GetTrailingTrivia()) | ||
| .WithAdditionalAnnotations(Simplifier.Annotation)); | ||
| } | ||
| } | ||
| } |
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35 changes: 35 additions & 0 deletions
35
src/EcoCode.Tests/LiveWarnings/EC82_VariableCanBeMadeConstantLiveWarnings.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,35 @@ | ||
| namespace EcoCode.Tests; | ||
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| internal static class VariableCanBeMadeConstantLiveWarnings | ||
| { | ||
| public static void Test1() | ||
| { | ||
| int i = 0; // EC82: Variable can be made constant | ||
| Console.WriteLine(i); | ||
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| int j = 0; | ||
| Console.WriteLine(j++); | ||
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| const int k = 0; | ||
| Console.WriteLine(k); | ||
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| int m = DateTime.Now.DayOfYear; | ||
| Console.WriteLine(m); | ||
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| int n = 0, o = 0; // EC82: Variable can be made constant | ||
| Console.WriteLine(n); | ||
| Console.WriteLine(o); | ||
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| object p = "abc"; | ||
| Console.WriteLine(p); | ||
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| string q = "abc"; // EC82: Variable can be made constant | ||
| Console.WriteLine(q); | ||
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| var r = 4; // EC82: Variable can be made constant | ||
| Console.WriteLine(r); | ||
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| var s = "abc"; // EC82: Variable can be made constant | ||
| Console.WriteLine(s); | ||
| } | ||
| } |
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