dotnet/roslyn

IDE0200 (remove unnecessary lambda expression) can change semantics when capturing writable members

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#73,259 opened on Apr 29, 2024

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Area-IDEBugFeature - IDE0200help wanted

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Description

Version Used:

Steps to Reproduce:

public class Test {
  private List<int> _list = [1];

  public bool N() {
    var func = M();
    _list = [2];
    return func(2);
  }

  private Func<int, bool> M() {
    return x => _list.Contains(x); // IDE0200
  }
}

Diagnostic Id: IDE0200

Expected Behavior: The code fix should not be offered. It changes the semantics.

Actual Behavior: After applying the code fix, N returns false instead of true

I saw that this was fixed when capturing locals in #69101

Contributor guide

Research direction
Investigate how IDE0200 determines when a lambda expression is unnecessary. For writable members, the semantics differ because the captured variable can change between lambda creation and invocation. The fix should not offer the simplification when the captured member is writable and could be reassigned before the lambda is invoked. Study the existing fix for locals (#69101) and extend it to handle instance fields and properties.
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.
1-2 days
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#Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70