Add directives field to TSModuleDeclaration?

[overlookmotel]

From #3532, it seems like this is legal syntax and 'use strict'; should be interpreted as a Directive:

namespace Foo {
    'use strict';
    export const bar = 123;
}

Should we add a directives: Vec<'a, Directive<'a>> field to TSModuleDeclaration and fill it in the parser, using same logic as for functions?

[Boshen]

Babel parser hands out Directive nodes. We can do this.

[overlookmotel]

Babel doesn't use Directives, as far as I can see, and nor does typescript-eslint or SWC:

AST explorer - Babel
AST explorer - typescript-eslint
AST explorer - SWC

They all produce a StringLiteral. But I think they're all doing it wrong!

We could just ignore this, and leave it as is. It's not at all a common case. But it will cause semantic to be incorrect. This should be an error (even if alwaysStrict: false in TS config), but it won't be:

namespace Foo {
    'use strict';
    let arguments;
}

Typescript gets this right: TS playground

NB: If we do this, we'd need to add a custom Serialize impl to get ESTree-compatible JSON AST output.