Re-exporting imports and CreateImportBinding assertions

Adam Klein adamk at chromium.org
Wed Apr 1 23:31:08 UTC 2015


I have a question about CreateImportBinding(N, M, N2) (where N is the name
to create in the importing module, and M is a module which exports N2).

Step 4 of
https://people.mozilla.org/~jorendorff/es6-draft.html#sec-createimportbinding
is the following assertion

"Assert: When M.[[Environment]] is instantiated it will have a direct
binding for N2."

What about the case were M is simply re-exporting an import? Consider:

---------
module 'a':

import { x } from 'b';

---------
module 'b':

import { x } from 'c';
export { x };

---------
module 'c':

export let x = 42;

---------

In this case, when running CreateImportBinding(x, 'b', x) in module 'a',
the assertion fails, as x in 'b' is an "immutable indirect binding" (itself
created by CreateImportBinding).

Is there a need for this assert I'm missing? I don't think skipping over
this assert, or removing "direct" from its wording,  will cause any
problems. Also, the term "direct binding" is not defined anywhere that I
can find, except as the negation of the "indirect" binding created by
CreateImportBinding.

Note that there's a similar issue in ResolveExport: step 4.a.i of
https://people.mozilla.org/~jorendorff/es6-draft.html#sec-resolveexport
asserts that resolved exports found in [[LocalExportEntries]] are "leaf
bindings" (another term that goes undefined), where by the usual CS
definition of "leaf" the assertion would be false for x in 'b' (when
resolved from 'a').

- Adam
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