Unexpected "used before its declaration" error when implementing a exported type of a merged namespace

Bug Report

🔎 Search Terms

used before its declaration vscode

🕗 Version & Regression Information

• tested in 4.7.3, 5.0.4 and nightly

⏯ Playground Link

Playground link with relevant code

💻 Code

namespace Foo {
    export interface Bar { }
}

class X implements Foo.Bar {

}

const Foo = 1;

🙁 Actual behavior

In VSCode it reports:

namespace Foo
Block-scoped variable 'Foo' used before its declaration.ts(2448)
Untitled-1(9, 7): 'Foo' is declared here.
Variable 'Foo' is used before being assigned.ts(2454)

You may not see the error immediately if you paste the code into a new file. It will appear when you start typing something.

Note that the error cannot be reproduced in the playground.

🙂 Expected behavior

No error.

Inizia con l’esempio TypeScript fornito e il link al Playground, quindi confronta la diagnostica dell’editor con il comportamento del Playground per il namespace unito e il tipo esportato. Segui il percorso del controllo dei tipi che segnala gli errori "used before its declaration" e "used before being assigned", quindi aggiungi un test di regressione che mostri che questo codice non produce errori.