microsoft / microsoft/TypeScript
the types 'T' and 'typeof Class' have no overlap
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Bug
Domain: check: Control Flow
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Description
Bug Report
🔎 Search Terms
template class no overlap label:Bug
🕗 Version & Regression Information
4.3.4 / 4.4.0-dev.20210617 / Nightly Playground
⏯ Playground Link
💻 Code
class Class {
dummy = 0;
}
function test<T>(a:T):void{
if (a === Class) {} // This condition will always return 'false' since the types 'T' and 'typeof Class' have no overlap.ts(2367)
}
🙁 Actual behavior
ts2367 error. a can be Class
🙂 Expected behavior
no error. a can be Class
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
Start with the linked Playground and reproduce diagnostic ts2367 using the generic test example and comparison with typeof Class. Trace the type-checking path that reports the no-overlap error, then add a regression test showing that the comparison is accepted when T can be Class.
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
- Clearly specified
- Newbie friendliness
- 35/100