1481024 - Stop relying on lexical variables being accessible across frame scripts

Status: RESOLVED FIXED

(Core :: Disability Access APIs, enhancement)

Description

[Kris Maglione [:kmag]]

The accessibility tests currently rely, in a lot of places, on certain lexical variables defined in global frame scripts being available to frame scripts run in unique scopes. While that is (unfortunately) the case now, it will not be after bug 1480244.

The most pervasive problem is ContentTask tasks which expect to be able to access a `document` variable, which is defined as a lexical in a global frame script. And, while the simplest way to solve this would be to use `var` rather than `let` to define these variables (which would define them as properties on the message manager rather than lexicals), storing `document`, `window`, and `navigator` references from a content window in a frame script scope is a very bad idea in general, since they remain alive even after the document navigates, after which they point to a document which is unrelated to the one currently loaded by the frameloader.

So instead, I opted to change the existing code to always access these things via `content` directly, rather than relying on the unsafe stub variables.

Comment 1

[Kris Maglione [:kmag]]

Attachment: Bug 1481024: Stop relying on lexical variables being available across frame scripts.

The accessibility tests currently rely, in many places, on lexical variables
defined in global frame scripts being available to other non-global frame
scripts. While that is currently the case, it will stop being so soon.

And, while the simplest solution would be to define them as properties on the
frame message manager by using `var` rather than `let`, storing references to
the current content window in a frame script scope is unsafe at best, and
should be avoided at all costs.

Review commit: https://reviewboard.mozilla.org/r/261384/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/261384/

Comment 2

[Yura Zenevich [:yzen] (please use "needinfo")]

Comment on attachment 8997682 [details]
Bug 1481024: Stop relying on lexical variables being available across frame scripts.

https://reviewboard.mozilla.org/r/261384/#review268738

thanks

Comment 3

[Kris Maglione [:kmag]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/c2e822179070687fce86468933a404f558490df7
Bug 1481024: Stop relying on lexical variables being available across frame scripts. r=yzen

Comment 4

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/c2e822179070