Currently the flow parser plugin accepts

declare export * from "./module.json" assert { type: "json" }
declare export * as ns from "./module.json" assert { type: "json" }
declare export { default } from "./module.json" assert { type: "json" }

None of them are supported by Flow as of Jun 2022.

However only

declare export * from "./module.json" assert { type: "json" }

works on generator because the DeclareExportAllDeclaration reuses the ExportAllDeclaration printer.

There are two solutions:

1. Add the missing assertions type definition to DeclareExportDeclaration and add the generator support
2. Throw an error (i.e. JSON modules are not yet supported in Flow) when DeclareExport*Declaration have assertions and remove the generator support mentioned above

While I personally think Flow should eventually support declared JSON modules imports. I am good with either supporting it prior to the Flow project or disabling it.

Note that

declare export default from "./module.json" assert { type: "json" }

is not supported when Flow and exportDefaultFrom are both enabled, though the error message "Missing semicolon. (1:27)" after from is not very helpful.

While I personally think Flow should eventually support declared JSON modules imports. I am good with either supporting it prior to the Flow project or disabling it.

I tend to do that too.

@liuxingbaoyu I am not sure I can follow. Do you tend to agree that we should support import assertions in Flow declare exports or disallow it (like Flow current does)?

Yes, I prefer to disable them before they actually work.