"Unassigned local" error for reference to "out var" in lambda with error parameter

Description

using System;
class C
{
    static void Main()
    {
        G((x, y) => y > 0 && F(out var z) && z > 0);
    }
    static bool F(out int i)
    {
        i = 0;
        return true;
    }
    static void G(Func<int, bool> f, object o) { }
    static void G(Func<int, bool> f, object x, object y) { }
}

(6,9): error CS1501: No overload for method 'G' takes 1 arguments
(6,46): error CS0165: Use of unassigned local variable 'z'

Contributor guide

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.

4

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

over 1 week

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

C#lambda expressionsout variablesdefinite assignment

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

20

Research direction

Investigate the definite assignment analyzer in the Roslyn compiler, specifically how it handles 'out var' declarations within lambda expressions. Look at the flow analysis logic for variables captured in lambdas. The issue reproduces with a specific overload resolution causing CS0165 falsely. Check the handling of 'out' parameters in nested scopes and ensure the assignment state propagates correctly.