microsoft / microsoft/TypeScript
`Tuple & nominal` not recognised as tuple in spread parameter
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Description
Bug Report
🔎 Search Terms
Nominal, Spread, Tuple,
🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about spread and intersections
⏯ Playground Link
Playground link with relevant code
💻 Code
declare let a: [number, number, number] & { _nominal_a: never }
function b(...params: [number, number, number]) {}
b(...a) // Error: A spread argument must either have a tuple type or be passed to a rest parameter.
🙁 Actual behavior
The error in the code example is thrown, because TypeScript does not detect it as being a tuple.
In roblox-ts, we use a nominal marker type to indicate a special kind of tuple. This bug means that this tuple type can then not be spreaded into a fixed argument function. Our issue: https://github.com/roblox-ts/roblox-ts/issues/1537
🙂 Expected behavior
This is a tuple type, and should therefore be recognised as such.
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 TypeScript Playground example and reproduce the spread error for the intersection of a tuple and nominal marker type. Trace the tuple and spread-argument checking behavior, then add a regression test covering this case; done means the fixed-parameter call type-checks without the spread error.
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
- 38/100