The set has to be static at module creation time. i.e. you could do this:

async function wrapModuleHidingX(url) {
  const source = await import.source(url);
  const names = source.exportNames().filter(name => name !== "x");
  return new ModuleSource(`
    export { ${ names.join(",") } } from "${url}";
  `);
}

From the modules call today:

// mod1
export let a;
export { a as b };

// mod2
export { a as x } from "mod1";

// mod3
export { b as x } from "mod3";

// mod4
export * from "mod2"
export * from "mod3"

If the use case is to detect not-actually-ambiguous ambigous re-exports, then the source of mod1 needs a way to say that a and b internally refer to the same local binding

We were considering supporting a single exports() with form { exportName, importName, localName, module }, where the existence of module implies reexports.

Our discussion today was that it might make sense to update exports() to return an object, but still leave out this binding info for now until we have a use case. But that by returning an object we could be forwards compatible with full bindings information if needed in future.