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Add Path.Combine/Join collapsing analyzer with fixers and tests
Co-authored-by: stephentoub <[email protected]>
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‎src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.CSharp.NetAnalyzers/Microsoft.NetCore.Analyzers/Performance/CSharpCollapseMultiplePathOperations.Fixer.cs‎

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// Copyright (c) Microsoft. All Rights Reserved. Licensed under the MIT license. See License.txt in the project root for license information.
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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 System.Threading;
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using System.Threading.Tasks;
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using Analyzer.Utilities;
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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;
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using Microsoft.CodeAnalysis.CSharp.Syntax;
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using Microsoft.CodeAnalysis.Editing;
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using Microsoft.NetCore.Analyzers;
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using Microsoft.NetCore.Analyzers.Performance;
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namespace Microsoft.NetCore.CSharp.Analyzers.Performance
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{
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[ExportCodeFixProvider(LanguageNames.CSharp), Shared]
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public sealed class CSharpCollapseMultiplePathOperationsFixer : CodeFixProvider
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{
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public override ImmutableArray<string> FixableDiagnosticIds { get; } = ImmutableArray.Create(CollapseMultiplePathOperationsAnalyzer.RuleId);
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public 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 document = context.Document;
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var diagnostic = context.Diagnostics[0];
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var root = await document.GetRequiredSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
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var node = root.FindNode(context.Span, getInnermostNodeForTie: true);
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if (node is not InvocationExpressionSyntax invocation)
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{
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return;
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}
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context.RegisterCodeFix(
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CodeAction.Create(
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MicrosoftNetCoreAnalyzersResources.CollapseMultiplePathOperationsCodeFixTitle,
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createChangedDocument: cancellationToken => CollapsePathOperationAsync(document, invocation, cancellationToken),
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equivalenceKey: nameof(MicrosoftNetCoreAnalyzersResources.CollapseMultiplePathOperationsCodeFixTitle)),
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diagnostic);
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}
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private static Task<Document> CollapsePathOperationAsync(Document document, InvocationExpressionSyntax invocation, CancellationToken cancellationToken)
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{
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// Collect all arguments by recursively unwrapping nested Path.Combine/Join calls
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var allArguments = CollectAllArguments(invocation);
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// Create new argument list with all collected arguments
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var newArgumentList = SyntaxFactory.ArgumentList(
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SyntaxFactory.SeparatedList(allArguments));
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// Create the new invocation with all arguments
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var newInvocation = invocation.WithArgumentList(newArgumentList)
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.WithTriviaFrom(invocation);
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var oldRoot = document.GetSyntaxRootAsync(cancellationToken).Result!;
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var newRoot = oldRoot.ReplaceNode(invocation, newInvocation);
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return Task.FromResult(document.WithSyntaxRoot(newRoot));
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}
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private static ArgumentSyntax[] CollectAllArguments(InvocationExpressionSyntax invocation)
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{
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var arguments = ImmutableArray.CreateBuilder<ArgumentSyntax>();
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foreach (var argument in invocation.ArgumentList.Arguments)
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{
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if (argument.Expression is InvocationExpressionSyntax nestedInvocation &&
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IsPathCombineOrJoin(nestedInvocation, out var methodName) &&
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IsPathCombineOrJoin(invocation, out var outerMethodName) &&
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methodName == outerMethodName)
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{
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// Recursively collect arguments from nested invocation
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arguments.AddRange(CollectAllArguments(nestedInvocation));
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}
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else
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{
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arguments.Add(argument);
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}
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}
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return arguments.ToArray();
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}
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private static bool IsPathCombineOrJoin(InvocationExpressionSyntax invocation, out string methodName)
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{
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methodName = string.Empty;
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if (invocation.Expression is MemberAccessExpressionSyntax memberAccess)
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{
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var name = memberAccess.Name.Identifier.Text;
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if ((name == "Combine" || name == "Join") &&
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memberAccess.Expression is IdentifierNameSyntax identifier &&
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identifier.Identifier.Text == "Path")
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{
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methodName = name;
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return true;
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}
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// Also handle fully qualified names like System.IO.Path
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if ((name == "Combine" || name == "Join") &&
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memberAccess.Expression.ToString().EndsWith("Path"))
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{
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methodName = name;
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return true;
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}
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}
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return false;
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}
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}
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}

‎src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers.md‎

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|CodeFix|True|
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---
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## [CA1876](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1876): Collapse consecutive Path.Combine or Path.Join operations
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When multiple Path.Combine or Path.Join operations are nested, they can be collapsed into a single operation for better performance and readability.
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|Item|Value|
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|-|-|
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|Category|Performance|
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|Enabled|True|
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|Severity|Info|
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|CodeFix|True|
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---
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## [CA2000](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2000): Dispose objects before losing scope
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If a disposable object is not explicitly disposed before all references to it are out of scope, the object will be disposed at some indeterminate time when the garbage collector runs the finalizer of the object. Because an exceptional event might occur that will prevent the finalizer of the object from running, the object should be explicitly disposed instead.

‎src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers.sarif‎

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]
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}
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},
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"CA1876": {
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"id": "CA1876",
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"shortDescription": "Collapse consecutive Path.Combine or Path.Join operations",
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"fullDescription": "When multiple Path.Combine or Path.Join operations are nested, they can be collapsed into a single operation for better performance and readability.",
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"defaultLevel": "note",
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"helpUri": "https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1876",
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"properties": {
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"category": "Performance",
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"isEnabledByDefault": true,
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"typeName": "CollapseMultiplePathOperationsAnalyzer",
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"languages": [
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"C#",
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"Visual Basic"
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],
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"tags": [
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"Telemetry",
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"EnabledRuleInAggressiveMode"
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]
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}
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},
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"CA2000": {
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"id": "CA2000",
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"shortDescription": "Dispose objects before losing scope",

‎src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/AnalyzerReleases.Unshipped.md‎

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CA1873 | Performance | Info | AvoidPotentiallyExpensiveCallWhenLoggingAnalyzer, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1873)
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CA1874 | Performance | Info | UseRegexMembers, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1874)
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CA1875 | Performance | Info | UseRegexMembers, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1875)
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CA1876 | Performance | Info | CollapseMultiplePathOperationsAnalyzer, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1876)
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CA2023 | Reliability | Warning | LoggerMessageDefineAnalyzer, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2023)
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CA2024 | Reliability | Warning | DoNotUseEndOfStreamInAsyncMethods, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2024)
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CA2025 | Reliability | Disabled | DoNotPassDisposablesIntoUnawaitedTasksAnalyzer, [Documentation](https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2025)

‎src/Microsoft.CodeAnalysis.NetAnalyzers/src/Microsoft.CodeAnalysis.NetAnalyzers/Microsoft.NetCore.Analyzers/MicrosoftNetCoreAnalyzersResources.resx‎

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<data name="DoNotUseThreadVolatileReadWriteCodeFixTitle" xml:space="preserve">
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<value>Replace obsolete call</value>
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</data>
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<data name="CollapseMultiplePathOperationsTitle" xml:space="preserve">
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<value>Collapse consecutive Path.Combine or Path.Join operations</value>
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</data>
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<data name="CollapseMultiplePathOperationsMessage" xml:space="preserve">
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<value>Multiple consecutive Path.{0} operations can be collapsed into a single operation</value>
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</data>
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<data name="CollapseMultiplePathOperationsDescription" xml:space="preserve">
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<value>When multiple Path.Combine or Path.Join operations are nested, they can be collapsed into a single operation for better performance and readability.</value>
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</data>
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<data name="CollapseMultiplePathOperationsCodeFixTitle" xml:space="preserve">
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<value>Collapse into single Path operation</value>
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</data>
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</root>

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