Microsoft/TypeScript

Noncrashing property access through non-null assertion operator should narrow that property to NonNullable

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#15,655 创建于 2017年5月8日

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 (11 评论) (1 反应) (0 负责人)TypeScript (48,455 star) (6,726 fork)batch import
BugDomain: check: Control FlowHelp Wanted

描述

TypeScript Version: 2.3 (Playground)

Code

Using strictNullChecks.

interface Foo {
    optional?: number;
}

interface Bar {
    foo?: Foo;
}

function test(bar: Bar) {
    if (bar.foo!.optional) {
        let num: number = bar.foo.optional;
    }

    if (bar.foo && bar.foo.optional) {
        let num: number = bar.foo.optional;
    }
}

Expected behavior: No errors or warnings.

Actual behavior:

  • num in first if block is number | undefined
  • bar.foo in first if block can be undefined

skarmavbild 2017-05-08 kl 12 58 06

贡献者指南

技术栈
typescript
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
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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
TypeScript basicsstrictNullCheckscontrol flow analysis
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。
25
研究方向
Investigate how the non null assertion (!) on property access is handled in control flow narrowing. Compare the narrowing behavior when using the non null assertion versus a simple truthy check (&&). The fix likely involves the checker's handling of NonNullExpression in narrowing of property types. Examine files such as checker.ts for the type narrowing logic, specifically how property access after a non null assertion is treated.