dotnet/roslyn

IDE0059 incorrectly suggests removal of used variable

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#64,044 opened on Sep 15, 2022

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Area-IDEBugFeature - IDE0059help wanted

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Description

Version Used: Microsoft Visual Studio Enterprise 2022 (64-bit) - Current Version 17.3.3, TargetFramework net6.0

Steps to Reproduce:

int count;
try
{
    if (0 == 1) { } // comment out to "fix" suggestion
    Console.WriteLine(); // comment out to "fix" suggestion
}
finally
{
    count = 3;
}

if (count == 0) { }

Expected Behavior: Do not delete my variable assignment.

Actual Behavior: Wants to break my code. If I follow the suggestion it removes the variable. It can alter the code semantics by deleting necessary assignments. In my example the compiler will error because count was not assigned but it could be more subtle. If you comment out either statement in the try block, the suggestion will disappear.

Contributor guide

Research direction
Investigate the control flow analysis in the unused variable analyzer, specifically how it handles try finally blocks where variable is assigned in finally.
Tech stack
csharp
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65