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Rest tuple parameter with intersection/union places error on wrong argument #28505
Description
TypeScript Version: 3.2.0-dev.20181113
Search Terms:
rest tuple, intersection, union, error, argument, misplaced
Code
declare function boop<T extends any[]>(...args: T & [number, string]): void;
boop(123, 456); // error
// ~~~ <-- error on first argument
// Argument of type '[123, 456]' is not assignable to parameter
// of type '[number, number] & [number, string]'.
// Type '[123, 456]' is not assignable to type '[number, string]'.
// Type '456' is not assignable to type 'string'.Expected behavior:
I expect an error on the second argument (456), since that's the argument that causes the failure, as made evident by the error message. (Or possibly I expect an error on both arguments, if it's interpreted as a failure to match the rest parameter.)
Actual behavior:
The actual error is on the first argument (123). This is a minor problem, and it only seems to show up in the intersection-with-type-parameter situation above (concrete types like ...args: [number, string] & [number, string] work fine), but I figured I'd report it in case it has an easy fix.
(Note to self or interested non-selves: ran into this in a Stack Overflow answer)
Playground Link:
🔗
Related Issues:
Haven't found anything. Anyone find anything?
Activity
jack-williams commentedon Nov 13, 2018
Think the same happens with unions too:
jcalz commentedon Jan 16, 2021
I see generics aren't even needed to reproduce this:
Playground link
[-]Inferred tuple type rest parameter with intersection seems to place error on wrong argument[/-][+]Tuple type rest parameter with intersection/union places error on wrong argument[/+][-]Tuple type rest parameter with intersection/union places error on wrong argument[/-][+]Rest tuple parameter with intersection/union places error on wrong argument[/+]