Microsoft/TypeScript

Missing error if ClassDeclaration is used in Statement position

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#22,682 创建于 2018年3月18日

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 (4 评论) (0 反应) (0 负责人)TypeScript (48,455 star) (6,726 fork)batch import
BugDomain: ParserEffort: CasualHelp Wanted

描述

TypeScript Version: 2.8.0-dev.20180318

Search Terms: class statement

Code

let codition = false as boolean;

if (condition)
    class C {} // runtime error if transpiled to ES2015 or above: Unexpected token class
if (condition)
    enum E { Foo } // should probably be an error?

new C(); // runtime error if transpiled to ES5, because 'C' is undefined
E.Foo; // runtime error: cannot read property 'Foo' of 'E'

Expected behavior:

Expected a compile error on class C and maybe on enum E

Actual behavior: no error for these declarations, instead I get a runtime error when targeting ES2015 or above.

Playground Link:

Related Issues:

贡献者指南

技术栈
typescript
领域
backend
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
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无
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。
65
研究方向
The issue involves the TypeScript compiler's parser or checker not raising an error when a class declaration appears as a statement after an if without braces. Investigate the parser logic in `src/compiler/parser.ts` where class declarations are parsed, and the checker in `src/compiler/checker.ts` for missing error reporting. The expected behavior is to emit an error similar to other disallowed statements. The issue is open and unassigned, making it a potential first contribution.