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Add code fix for redundant exception declarations (#295)
* Add code fix for redundant exception declarations * Update CHANGELOG.md * Fix tests
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‎CHANGELOG.md‎

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@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
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## Unreleased
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### Added
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- PR [#295](https://github.com/marinasundstrom/CheckedExceptions/pull/295) Code fix to remove redundant exception declarations
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## [2.2.0] - 2025-08-23
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### Added

‎CheckedExceptions.CodeFixes/CodeFixReleases.Unshipped.md‎

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### New Rules
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- THROW017: Materialize deferred enumeration with ToArray
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- THROW012: Remove redundant exception declaration

‎CheckedExceptions.CodeFixes/RemoveRedundantExceptionDeclarationCodeFixProvider.cs‎

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using System.Collections.Immutable;
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using System.Composition;
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using System.Linq;
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using Microsoft.CodeAnalysis;
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using Microsoft.CodeAnalysis.CodeActions;
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using Microsoft.CodeAnalysis.CodeFixes;
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using Microsoft.CodeAnalysis.CSharp.Syntax;
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using Microsoft.CodeAnalysis.Editing;
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using Microsoft.CodeAnalysis.Formatting;
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namespace Sundstrom.CheckedExceptions;
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[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(RemoveRedundantExceptionDeclarationCodeFixProvider)), Shared]
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public class RemoveRedundantExceptionDeclarationCodeFixProvider : CodeFixProvider
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{
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private const string TitleRemoveRedundantExceptionDeclaration = "Remove redundant exception declaration";
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public sealed override ImmutableArray<string> FixableDiagnosticIds =>
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[CheckedExceptionsAnalyzer.DiagnosticIdDuplicateDeclarations,
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CheckedExceptionsAnalyzer.DiagnosticIdDuplicateThrowsByHierarchy,
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CheckedExceptionsAnalyzer.DiagnosticIdRedundantExceptionDeclaration];
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public sealed override FixAllProvider GetFixAllProvider() =>
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WellKnownFixAllProviders.BatchFixer;
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public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
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{
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var diagnostic = context.Diagnostics.First();
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var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
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var node = root.FindNode(diagnostic.Location.SourceSpan, getInnermostNodeForTie: true);
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var argument = node.FirstAncestorOrSelf<AttributeArgumentSyntax>();
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if (argument is null)
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return;
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context.RegisterCodeFix(
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CodeAction.Create(
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title: TitleRemoveRedundantExceptionDeclaration,
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createChangedDocument: c => RemoveRedundantDeclarationAsync(context.Document, argument, c),
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equivalenceKey: TitleRemoveRedundantExceptionDeclaration),
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context.Diagnostics);
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}
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private static async Task<Document> RemoveRedundantDeclarationAsync(Document document, AttributeArgumentSyntax argument, CancellationToken cancellationToken)
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{
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var editor = await DocumentEditor.CreateAsync(document, cancellationToken).ConfigureAwait(false);
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var attribute = (AttributeSyntax)argument.Parent.Parent;
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var list = (AttributeListSyntax)attribute.Parent;
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if (attribute.ArgumentList?.Arguments.Count == 1)
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{
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if (list.Attributes.Count == 1)
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{
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editor.RemoveNode(list);
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}
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else
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{
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editor.RemoveNode(attribute);
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}
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}
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else
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{
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var newArguments = attribute.ArgumentList.Arguments.Remove(argument);
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var newAttribute = attribute
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.WithArgumentList(attribute.ArgumentList.WithArguments(newArguments))
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.WithAdditionalAnnotations(Formatter.Annotation);
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editor.ReplaceNode(attribute, newAttribute);
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}
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return editor.GetChangedDocument();
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}
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}

‎CheckedExceptions.Tests/CodeFixes/RemoveRedundantExceptionDeclarationCodeFixProviderTests.cs‎

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namespace Sundstrom.CheckedExceptions.Tests.CodeFixes;
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using System.Threading.Tasks;
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using Microsoft.CodeAnalysis.Testing;
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using Xunit;
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using Xunit.Abstractions;
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using Verifier = CSharpCodeFixVerifier<CheckedExceptionsAnalyzer, RemoveRedundantExceptionDeclarationCodeFixProvider, Microsoft.CodeAnalysis.Testing.DefaultVerifier>;
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public class RemoveRedundantExceptionDeclarationCodeFixProviderTests
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{
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[Fact]
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public async Task RemoveWholeAttribute()
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{
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var testCode = /* lang=c#-test */ """
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#nullable enable
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using System;
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public class C
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{
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[Throws(typeof(InvalidOperationException))]
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public void M()
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{
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}
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}
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""";
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var fixedCode = /* lang=c#-test */ """
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#nullable enable
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using System;
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public class C
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{
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public void M()
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{
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}
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}
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""";
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var expected = Verifier.Diagnostic(CheckedExceptionsAnalyzer.DiagnosticIdRedundantExceptionDeclaration)
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.WithArguments("InvalidOperationException")
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.WithSpan(6, 20, 6, 45);
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await Verifier.VerifyCodeFixAsync(testCode, [expected], fixedCode, setup: option =>
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{
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option.DisabledDiagnostics.Remove(CheckedExceptionsAnalyzer.DiagnosticIdRedundantExceptionDeclaration);
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});
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}
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[Fact]
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public async Task RemoveSingleArgumentFromAttribute()
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{
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var testCode = /* lang=c#-test */ """
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#nullable enable
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using System;
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public class C
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{
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[Throws(typeof(InvalidOperationException), typeof(ArgumentException))]
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public void M()
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{
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throw new ArgumentException();
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}
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}
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""";
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var fixedCode = /* lang=c#-test */ """
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#nullable enable
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using System;
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public class C
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{
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[Throws(typeof(ArgumentException))]
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public void M()
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{
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throw new ArgumentException();
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}
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}
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""";
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var expected = Verifier.Diagnostic(CheckedExceptionsAnalyzer.DiagnosticIdRedundantExceptionDeclaration)
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.WithArguments("InvalidOperationException")
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.WithSpan(6, 20, 6, 45);
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await Verifier.VerifyCodeFixAsync(testCode, [expected], fixedCode, setup: option =>
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{
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option.DisabledDiagnostics.Remove(CheckedExceptionsAnalyzer.DiagnosticIdRedundantExceptionDeclaration);
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});
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}
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}

‎docs/codefix-specification.md‎

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| ------------- | ------------------------------------- | ------------------------------------------------------------------------------------------------ |
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| **THROW001** | Unhandled exception type | 🔧 Add throws declaration<br>🧯 Surround with try/catch<br>➕ Add catch clause to surrounding try<br>➕ Introduce catch clause |
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| **THROW004** | Redundant typed catch clause | 🧹 Remove redundant catch clause |
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| **THROW005** | Redundant exception declaration | 🗑️ Remove redundant throws declaration |
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| **THROW005** | Duplicate exception declaration | 🗑️ Remove redundant throws declaration |
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| **THROW007** | Missing throws from base/interface | 🔧 Add throws declaration from base member |
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| **THROW011** | Missing throws from XML documentation | 🔧 Add throws declaration from XML doc |
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| **THROW012** | Redundant exception declaration | 🗑️ Remove redundant throws declaration |
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| **THROW013** | Redundant catch-all clause | 🧹 Remove redundant catch clause
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| **THROW014** | Catch clause has no remaining exceptions to handle | 🧹 Remove redundant catch clause
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| **THROW015** | Redundant catch clause | 🧹 Remove redundant catch clause
@@ -362,7 +363,8 @@ Func<int, int> f = x => x;
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**Applies to:**
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* `THROW005` – *Redundant exception declaration*
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* `THROW005` – *Duplicate exception declaration*
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* `THROW012` – *Redundant exception declaration*
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Removes a `[Throws]` declaration for an exception type that is **never thrown**.
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