Named Tuple elements should allow reserved words as their names

Bug Report

🔎 Search Terms

tuple elements label reserved word
named tuple elements

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about "Common "Bugs" That Aren't Bugs"

⏯ Playground Link

Playground link with relevant code

💻 Code

type x = [if: any]
// but some keywords are allowed, e.g.
type y = [void: any]

🙁 Actual behavior

Unused label.
'any' only refers to a type, but is being used as a value here.
Type expected.
'(' expected.
Unexpected keyword or identifier.
Declaration or statement expected.

🙂 Expected behavior

No errors. As a label it should allow any identifiers, including reserved words.

👩‍💻 Possible solution

Although parseTupleElementNameOrTupleElementType allows any identifier as its name:

https://github.com/microsoft/TypeScript/blob/0af2497fecef9e41d7d0260fd37932dd33912c66/src/compiler/parser.ts#L3559

before it is invoked, the isListElement requires a tuple member start a type:

https://github.com/microsoft/TypeScript/blob/0af2497fecef9e41d7d0260fd37932dd33912c66/src/compiler/parser.ts#L2091

This is no longer true after we support named tuple member after 4.0, which should start with any valid identifiers / keywords. Because isListElement returns false, the parser does not parse them as tuple elements, which results to confusing parsing errors.

We can create a new ParsingContext for named tuple members, and returns token() === SyntaxKind.CommaToken || tokenIsIdentifierOrKeyword(token()) in isListElement.

Bắt đầu trong src/compiler/parser.ts tại isListElement và parseTupleElementNameOrTupleElementType, sử dụng mã Playground được liên kết làm trường hợp tái hiện. Theo dõi cách các thành viên tuple có tên bắt đầu bằng một từ dành riêng được phân loại, sau đó thêm một regression test bao quát ví dụ và xác minh rằng nó không tạo ra lỗi phân tích cú pháp.