dotnet/roslyn

VB.NET AnalyzeDataFlow incorrectly reports parameters as WrittenInside

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#68,286 opened on May 22, 2023

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Description

Version Used: 4.6.0

Steps to Reproduce:

Use following source code to analyse

Public Sub Test(i As Integer)
    Dim s = i.ToString()
End Sub

with following visitor

public override SyntaxNode VisitMethodBlock(MethodBlockSyntax node)
{
    var first = node.Statements.First();
    var last = node.Statements.Last();
    var dataFlow = semanticModel.AnalyzeDataFlow(first, last);
    Debug.Assert(dataFlow.WrittenInside.Length == 1);

    return node;
}

Expected Behavior: dataFlow.WrittenInside should not contain Parameter i As System.Int32, only Local s As System.String

Actual Behavior: dataFlow.WrittenInside contains Parameter i As System.Int32.

Notes: Equivalent code in C# is analysed as expected, the parameter is not part of the dataFlow.WrittenInside.

I suspect this line: https://github.com/dotnet/roslyn/blob/687921ffae8ad91a5464473cb1759fd463c345f2/src/Compilers/VisualBasic/Portable/Analysis/FlowAnalysis/DataFlowPass.vb#L1537

Contributor guide

Research direction
Inspect the linked line in DataFlowPass.vb and trace how parameters are considered. Verify if the condition for detecting written variables incorrectly includes parameters.
Tech stack
csharp
Domain
backend
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.
1-3 hours
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#Visual BasicRoslyn
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60