noUncheckedIndexedAccess and variadic tuples

[TkDodo]

TypeScript Version: 4.1.0-dev.20200920

Search Terms:

• noUncheckedIndexedAccess
• Pedantic Index Signatures
• variadic tuples

Code

type NonEmptyStringArray = [string, ...Array<string>]

const strings: NonEmptyStringArray = ['one', 'two', 'three']

strings[0].toUpperCase()
strings[99].toUpperCase()

Expected behavior:

strings[99].toUpperCase() should type error

Actual behavior:

strings[99].toUpperCase() shows no type error

Please note that if you change const strings to Array<string>, every index access correctly yields a type error.

Playground Link:

https://www.typescriptlang.org/play?noUncheckedIndexedAccess=true&ts=4.1.0-dev.20200920#code/PTACDsHsFVwYwBYFM4GskBMCS4NIB6YCCccSAzuQFBUAuAngA5IAEAcpOAKIC2jDAZVoAnAJbgA5kWHCAhvRYBeFgG1yI8RIA0LAHT7pc+gB51YyQD4AujTid1LM5vIAudp1796Q81JnylVQByTiQgnSDaAHdIcJZIhGEkMJsqJ0lyFQAGK11aGEZmYQBhWXIkAAoASjSNDJUATgbc-OhCpBKyyqqgA

Related Issues:

#39560