dotnet/roslyn

Confusing error message for overloaded generic delegate-accepting method

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#8,603 建立於 2016年2月11日

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Area-CompilersBugConcept-Diagnostic Clarityhelp wanted

描述

I have the following code:

using System;

class Program
{
    static void Main()
    {
        M(x => { });
    }

    static void M(string s)
    {
    }

    static void M<T>(Action<T> a)
    {
    }
}

It produces the following error:

CS1660 Cannot convert lambda expression to type 'string' because it is not a delegate type

I think that a human can clearly see that the code is attempting to call the delegate-accepting overload, but is missing a type argument (M<int>(x => { });) or explicit parameter type (M((int x) => { });).

But the compiler shows error message that's related to the first (string-accepting) overload, which I think is confusing.

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csharp
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議題類型
bug
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
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clear
前置要求
C# overload resolutionRoslyn diagnostics infrastructure
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
60
研究方向
The issue describes a confusing error message CS1660 when calling an overloaded method with a lambda. The fix likely involves improving the overload resolution diagnostics in the Roslyn binder (e.g., Semantics/OverloadResolution). The issue is assigned (assignee not visible), so check the assignee's status before starting. Look at linked files in the compiler's error reporting for CS1660.
Confusing error message for overloaded generic delegate-accepting method · dotnet/roslyn#8603 | Good First Issue