Incorrect index signature parameter type error

[mbrodersen]

Version

$ ./node_modules/typescript/bin/tsc --version
Version 2.4.2

Code

type ClientId = number;

interface Clients {[key:ClientId]:any};

Expected behavior

No compiler errors.

Actual behavior

error TS1023: An index signature parameter type must be 'string' or 'number'.

Comment

ClientId is a number and Typescript is using structural typing - not nominative typing.

[RyanCavanaugh]

Duplicate #14934 and many others