Flow’s parser does not understand `export from` attributes (the `with { type: "json" }` syntax).

[sangafabrice]

Flow version: 0.295.0

Expected behavior

According to MDN:

export from supports all features that import supports — for example, import attributes.

So the following should be valid:

/** @file export.js */
export { default } from "./htmlhint.json" with { type: "json" };

/** @file index.js */
import ruleset from "./export.js";

console.log(ruleset);

Running:

node index.js

should output the contents of htmlhint.json as an object:

{ "tagname-lowercase": true }

And processing with Flow should succeed:

npx flow-remove-types --out-file ./export.out.js ./export.js --all

Expected result:

./export.js
 ↳ ./export.out.js

Actual behavior

Flow fails to parse the with { type: "json" } attribute on export from:

./export.js
 ↳ Syntax Error: ';' expected (2:42)
export { default } from "./htmlhint.json" with { type: "json" };
                                          ^
   1: export { default } from "./htmlhint.json" with { type: "json" };

• Link to Try-Flow or Github repo:
  https://flow.org/try/#1N4Igxg9gdgZglgcxALlAIwIZoKYBsD6uEEAztvhgE6UYCe+JADpdhgCYowa5kA0I2KAFcAtiRQAXSkOz9sADwxgJ+NPTbYuQ3BMnTZA+Y2yU4IwRO4A6SFBIrGVDGM7c+h46fNRLuKxJIGWh8MeT0ZfhYlCStpHzNsFBAMIQkIEQwJODAQfiEyfCEoAGsoCAB3KHw4KrBMsAALfAA3KjgsXGxxZC4eAw1m-GhcWn9aY3wWZlc+-g1mbDqJbDYAWglxxJ63AxJi7AlG2lXhXFwZ9z2Do5PRHEoLgyKwTqp1zce8qChFrpIqY41VqmDA+T4gIo-MB-AGrCCMLLQbirRoYGrgor-GDYVYIA7LSgkVZkCQE7q9dxFfIrVbMdJwMjghSeBIhPwYEhkSgqeEmTIQB7bPoAX34kA0SWZAokAAJgDKNFodDLhTKYJR0jKADogKwAegaEhEuAaNRiACsSNAdTLynAJA05TKNsZkNqQJbrSAVQBuXIgZomEhwaBJZoABisACYAJwAVis4ZAwqAA

[hiSandog]

Parser support for export ... from ... with { type: "json" } would be useful to track separately from typechecking semantics. Even if Flow does not act on the import attribute yet, accepting the syntax and preserving it in the AST would unblock codebases using modern bundler/Node syntax. A parser fixture covering both import ... with and export ... from ... with would make the scope clear.