microsoft / microsoft/TypeScript
typeof Foo['bar'] has strange precedence
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Description
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?
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
The issue names no files, tests, or entry points. Start by reproducing the AST for typeof Foo['bar'] and comparing it with the expected grouping; done means establishing the intended parse-tree behavior and covering the decision with an appropriate regression test.
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
- Needs clarification
- Newbie friendliness
- 30/100