Unexpected diagnostic in `with` expression with indexer on a struct

描述

    [Fact]
    public void TODO2()
    {
        var src = """
var c = new S() with { [0] = 1 };

public struct S
{
    public int this[int i] { set { } }
}
""";

        CreateCompilation(src).VerifyEmitDiagnostics(
            // (1,24): error CS0131: The left-hand side of an assignment must be a variable, property or indexer
            // var c = new S() with { [0] = 1 };
            Diagnostic(ErrorCode.ERR_AssgLvalueExpected, "[0]").WithLocation(1, 24),
            // (1,24): error CS0747: Invalid initializer member declarator
            // var c = new S() with { [0] = 1 };
            Diagnostic(ErrorCode.ERR_InvalidInitializerElementInitializer, "[0] = 1").WithLocation(1, 24));
    }

貢獻者指南

技術棧

csharp

領域

tooling

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

預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。

half day

活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。

fresh

清晰度議題是否清楚說明預期改動、驗收標準和下一步。

clear

前置要求

C# programmingRoslyn compiler basics

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 presents a test case where an unexpected diagnostic (CS0131) is emitted in a `with` expression with an indexer on a struct. The expected behavior is that only CS0747 should be reported. Investigate the Roslyn source code for handling `with` expressions, specifically in the semantic model or binding. Look at the error reporting for indexer initializers. The test file can be added to the existing test suite. The fix may involve modifying the code that emits ERR AssgLvalueExpected to suppress it when the construct is within a `with` expression initializer that already has an error. Check recent commits related to `with` expressions for context.