Spurious use of unassigned variable error with unimplemented partial

Description

public partial class C {
    public partial string M1(string dummyParam, out bool i); // error CS8795: Partial method 'C.M1(string, out bool)' must have an implementation part because it has accessibility modifiers.
    
    public void M2(C c)
    {
        c.M1(null, out bool i);
        _ = i.ToString(); // error CS0165: Use of unassigned local variable 'i'
    }
}

Contributor guide

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.

half day

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#partial methodsRoslyn compiler structure

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

65

Research direction

Investigate the compiler's flow analysis for partial methods, likely in the semantic model or binding stage. Check how errors CS8795 and CS0165 are emitted, and implement a suppression of CS0165 when CS8795 is already reported for the same method. See similar suppression patterns in the Roslyn codebase.