dotnet/roslyn

IDE0059 Incorrectly reported for out arguments

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#58,564 opened on Jan 3, 2022

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Area-IDEBugFeature - IDE0059help wanted

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Description

Version Used: 6.0

Steps to Reproduce:

class Test
{
		public static void Foo ()
		{
			int i;
			OutFoo (out i, 9); // error IDE0059: Unnecessary assignment of a value to 'i'
			OutFoo (out i, i);
            Console.WriteLine (i);
		}

		public static void OutFoo (out int i, int arg)
		{
			i = ++arg;
		}
}

Expected Behavior:

No IDE0059 reported

Actual Behavior:

error IDE0059: Unnecessary assignment of a value to 'i'

Contributor guide

Research direction
Investigate the IDE0059 analyzer's handling of out arguments. Look at how the analyzer tracks assignments to variables passed as out arguments. The issue is that the analyzer incorrectly flags the variable 'i' in 'OutFoo(out i, 9)' as having an unnecessary assignment, but the assignment is necessary because the variable is used as an argument to 'OutFoo' again. Trace the dataflow analysis for out parameters and ensure that assignments before the first use are not flagged when the variable is passed as an out argument.
Tech stack
csharp
Domain
developer experience
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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#out parameters
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70