microsoft / microsoft/TypeScript
Precedence in parsing types
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Description
It looks to me like this should parse, but it doesn't:
var x: number | (string)=>void;
It works with added parens:
var x: number | ((string)=>void);
But if the parser is not too hacky, then maybe it's easy to make the first work?
(FWIW, I ran into this in a rest argument, where it would be nice to avoid the extra parens in
function foo(...xs: (number | ()=>void)[]): void { }
)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Reproduce the two type-annotation examples and the rest-argument example from the issue, then inspect TypeScript's parser handling of union types and function types. Done means the unparenthesized form parses successfully without regressing the parenthesized forms or the rest-argument case.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100