Should named JSON module import be a parsing stage error?

[JLHwung]

Currently Babel parser throws syntax error for the following cases:

import { foo } from "./foo" asserts { type: "json" };

which conforms to this test262 test.

But the spec only states that JSON module should provide only a single default export, so a SyntaxError should be thrown no later than the module resolution stage. However unlike random modules, a parser can recognize JSON module imports thanks to the import assertion syntax. So should a JavaScript parser throw such errors?

Either way an end user will not observe any differences, but it helps us define the scope.

Context: babel/babel#14816

[ljharb]

It’s a host-dependent behavior, and the assertion is not supposed to be required outside a browser. It definitely should error, but probably not at the parsing stage.