Confusing error message when the target member cannot be located for an explicit interface implementation

Description

interface I100 { }

class C100 : I100
{
    object I100.M4() => null;
}

 error CS0539: 'C100.M4()' in explicit interface declaration is not found among members of the interface that can be implemented

Contributor guide

Tech stack

csharp

Domain

developer experiencetooling

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.

stale

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

clear

Prerequisites

C# explicit interface implementationRoslyn error reporting

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

50

Research direction

Examine the definitions of error CS0539 in Roslyn source, likely in src/Compilers/CSharp/Portable/Errors/ErrorCode.cs and related message strings. Identify where the condition for this error is emitted (possibly in Binder or OverloadResolution). The fix may involve adding a new error code or modifying the message to clarify that the method is not found in the class.