dotnet/roslyn

Private extension methods are shown as null-unaware

Open

#80648 opened on Oct 10, 2025

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Area-IDEhelp wanted

Description

Version Used: VS 18.0.0 Insiders [11109.219]

Steps to Reproduce: Show the quick info tooltip on each of the extension method invocations.

#nullable enable
static class Cx
{
    public static void M()
    {
        "".M1().M2().M3();
    }

    extension<T> (T s)
    {
        private T M1() => s;
        internal T M2() => s;
        public T M3() => s;
    }
}

Expected Behavior: As all extensions are declared in a nullable context, neither should show that is "not nullable aware".

Actual Behavior:

  • Hovering over M1() shows the signature and the notice "'M1' is not nullable aware."
  • Hovering over M2() and M3() shows the signature and no such notice.

Contributor guide

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.
3
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.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C# nullable reference typesextension methodsRoslyn nullable analysis
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Investigate why private extension methods in a nullable enabled context are reported as 'not nullable aware' while internal/public are not. Look at the Roslyn IDE layer (e.g., Microsoft.CodeAnalysis.CSharp.Features) for the quick info tooltip logic. Check if nullable awareness is incorrectly determined based on accessibility in the null state analysis. Consider the difference between private and non private extensions in the MethodSignatureDisplay or similar classes.