Microsoft/TypeScript

typeof Foo['bar'] has strange precedence

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#19,707 建立於 2017年11月3日

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 (6 留言) (0 反應) (0 負責人)TypeScript (48,455 star) (6,726 fork)batch import
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描述

Type queries combined with indexed access types currently produce a parse tree that is surprising in its behavior.

One would think that typeof Foo['bar'] would be parsed as typeof (Foo['bar']), which would really be something like typeof Foo.bar.

That's not the case. It's actually parsed as (typeof Foo)['bar'].

Conveniently, it seems that semantically (when type-checking) these are identical, but it seems strange for syntactic consumers. Do we believe this is currently working as intended?

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技術棧
typescript
領域
toolingdeveloper experience
議題類型
research
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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1-3 hours
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stale
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
TypeScript type systemcompiler parser 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。
30
研究方向
Investigate the parser implementation in src/compiler/parser.ts to see how typeof and indexed access types are parsed. Review the relevant grammar rules and check if the current behavior is deliberate. If not, propose a fix to change the parse tree. Additionally, check if any existing tests cover this precedence.