Rest declarations in destructured arrays receiving incorrect types from tuples declaring the types in the destructured array

[zajrik]

TypeScript Version: 2.3.4

Code

public async action([res, commandName, ...roleNames]: [ResourceLoader, string, string[]]): Promise<void> { ... }

Expected behavior:
When destructuring the method parameter (which can be an array of potentially anything after middleware has had its say, but I know exactly what it will be in this case) I've gathered the remaining array values (which I know to be strings) into roleNames and declared the type of the variables in the destructured array via the tuple [ResourceLoader, string, string[]].

I expect roleNames to take on the declared type from the tuple as res and commandName have correctly done.

Actual behavior:
When hovering over the roleNames declaration I get the following:

var roleNames: (string | ResourceLoader | string[])[]

Apologies for the convoluted title. Couldn't think of a less verbose description.

[DanielRosenwasser]

The type [ResourceLoader, string, string[]] probably isn't what you had in mind. What you really want is an open-ended tuple where all of the trailing elements are known to be strings.

Generally related is #5453.

[zajrik]

I've actually recently re-engineered the code in question because it allowed me to merge the functionality of two separate things into one, so I'm actually just receiving a string where ...roleNames used to exist and parsing potentially multiple roles within the function body, but I am still interested in a resolution to this problem.

I'm not entirely sure what you mean by open-ended tuple. Given what you've linked is a proposal, is this something that is possible in current TS?

[ahejlsberg]

Now implemented in #24897.

[zajrik]

I somehow missed seeing this get closed, but I saw this change in the 3.0 RC and thought "Hey, that was my issue!"

Glad to see this resolved. Cheers 🎉