Document IDE0059 analyzer limitations in try/catch, lambdas, and other contexts

[Copilot]

IDE0059 fails to detect unused value assignments in try/catch blocks, lambda expressions, using statements, and expression trees. This is a known Roslyn analyzer limitation tracked across multiple issues but not documented.

Changes

• Added "Known limitations" section after the overview, listing the four contexts where the analyzer fails
• Included example showing undetected unused assignment in try/catch block
• Linked to five related Roslyn issues (#52292, #65220, #74219, #81742, #80033) for tracking

public void Example()
{
    try
    {
        // This unused assignment isn't flagged by IDE0059
        var unused = new object();
    }
    catch (Exception ex)
    {
        // Handle exception
    }
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[UUF] Rule doesn't work in functions</issue_title>
<issue_description>### Type of issue

Missing information

Description

This rule doesn't work in most functions, that should be documented here until it does. See dotnet/roslyn#52292 and related issues.

Page URL

https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/ide0059

Content source URL

https://github.com/dotnet/docs/blob/main/docs/fundamentals/code-analysis/style-rules/ide0059.md

Document Version Independent Id

bbb0a386-bae8-0208-eafa-314dde4f2f50

Platform Id

73482376-16ba-6845-bbd9-f4bb0045e4bc

Article author

@gewarren

Metadata

• ID: 9a027032-b737-2b53-f6f3-b4787aa45a31
• PlatformId: 73482376-16ba-6845-bbd9-f4bb0045e4bc
• Service: dotnet-fundamentals

Related Issues</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [UUF] Rule doesn't work in functions #50733

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

---

Internal previews

📄 File	🔗 Preview link
docs/fundamentals/code-analysis/style-rules/ide0059.md	Remove unnecessary value assignment (IDE0059)

[Copilot]

Pull request overview

This PR documents known limitations of the IDE0059 analyzer rule by adding a new "Known limitations" section that describes four specific contexts where the analyzer fails to detect unused value assignments.

Key changes:

• Updated the ms.date field to reflect the current date (01/05/2026)
• Added a "Known limitations" section after the "Overview" section explaining where IDE0059 doesn't work
• Included references to five related GitHub issues tracking these limitations

Comments suppressed due to low confidence (1)

docs/fundamentals/code-analysis/style-rules/ide0059.md:15

• According to the .NET Documentation Guidelines, for any Markdown files generated with AI assistance, you must add the ai-usage frontmatter key/value pair. Since this content was generated by Copilot (as indicated in the PR metadata), you should add "ai-usage: ai-assisted" to the frontmatter section.

---
title: "IDE0059"
description: "Learn about code analysis style rule IDE0059."
ms.date: 01/05/2026
f1_keywords:
- IDE0059
- csharp_style_unused_value_assignment_preference
- visual_basic_style_unused_value_assignment_preference
helpviewer_keywords:
- IDE0059
- csharp_style_unused_value_assignment_preference
- visual_basic_style_unused_value_assignment_preference
author: gewarren
ms.author: gewarren
zone_pivot_groups: code-language