Result of unknown indexing explicitly cast to `any` incorrectly reported as implicit any

TypeScript Version: typescript@3.4.0-dev.20190311

Search Terms: "Element implicitly has an 'any' type" " index expression is not of type"

We are on the same page that an unknown/untyped indexing operation results in an any result. However, it seems that silence the error the object being indexed must be cast to any, it is insufficient to cast the result of the indexing itself to any.

Code

declare let foo: HTMLElement;

let a = (<any>foo.attributes)["bar"].value;

let x = foo.attributes["bar"].value;
let y = (<any>foo.attributes["bar"]).value;
let z = (foo.attributes["bar"] as any).value;

compiled with tsc --strict ./test.ts

Expected behavior:

• No error on let a = ... because type warnings on any operation on an explicitly any type (including indexing) are let through.
• An error is thrown on let x = ... because the element type resulting from the lookup is of unknown type.
• No error on let y = ..., not because the type is known but because I'm explicitly casting the <any> result to any.
• No error on let z = ..., not because the type is known but because I'm explicitly casting the <any> result to any.

Actual behavior:

test.ts:3:24 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'.

3 let x = foo.attributes["bar"].value;
                         ~~~~~

test.ts:4:30 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'.

4 let y = (<any>foo.attributes["bar"]).value;
                               ~~~~~

test.ts:5:25 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'.

5 let z = (foo.attributes["bar"] as any).value;
                          ~~~~~

I argue that both (<any>foo)["bar"] and (<any> (foo["bar"])) should not trigger this error.

Riproduci le quattro espressioni con typescript@next usando tsc --strict ./test.ts, quindi traccia il modo in cui vengono prodotti i diagnostici di accesso indicizzato per i casi mostrati. Il lavoro è completato quando x continua a segnalare TS7015, mentre i casi a, y e z convertiti esplicitamente non lo fanno.