dotnet/roslyn

ref local gives bad error when inited with ternary initializer

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#22,048 创建于 2017年9月11日

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 (5 评论) (0 反应) (0 负责人)C# (20,414 star) (4,257 fork)batch import
Area-CompilersConcept-Diagnostic ClarityFeature - Readonly ReferencesLanguage-C#Testhelp wanted

描述

Version Used: 2.3.1.61919 (57c81319) - on OSX with mono 5.4.0.135

Steps to Reproduce:

Compile this:

using System;

class Driver {
	static int X;
	static void Main () {
		ref int x = X == 0 ? ref X : ref X;
	}
}

Expected Behavior:

It should either compile or give a clear error message that what I'm doing is wrong

Actual Behavior:

Microsoft (R) Visual C# Compiler version 2.3.1.61919 (57c81319)
Copyright (C) Microsoft Corporation. All rights reserved.

ref2.cs(6,24): error CS1525: Invalid expression term 'ref'
ref2.cs(6,24): error CS1003: Syntax error, ':' expected
ref2.cs(6,24): error CS1002: ; expected
ref2.cs(6,30): error CS1001: Identifier expected
ref2.cs(6,30): error CS1002: ; expected
ref2.cs(6,30): error CS1513: } expected
ref2.cs(6,37): error CS1001: Identifier expected

I tried all combinations of adding/removing ref and parens and nothing worked. The only one that gave me something good was ref int x = ref (X == 0 ? X : X); with: error CS1510: A ref or out value must be an assignable variable

贡献者指南

技术栈
csharp
领域
developer experience
议题类型
bug
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
1-3 hours
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
stale
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
Familiarity with C# ref localsBasic understanding of Roslyn's syntax parserKnowledge of error generation in the compiler
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
35
研究方向
Investigate how the Roslyn parser handles ternary conditional expressions involving ref locals. Start by looking at the syntax parser for conditional expressions (likely in SyntaxParser.cs) and the error generation logic for invalid expression terms. Check if there are any existing tests for similar cases. The issue reporter suggests that 'ref int x = ref (X == 0 ? X : X);' gives a better error, so the fix may involve improving the parser's recognition of 'ref' in ternary initializers.