1573625 - Fix usage of nsIDocShellTreeItem in nsCoreUtils::IsRootDocument

Status: NEW

(Core :: Disability Access APIs, enhancement, P2)

Description

[Kannan Vijayan [:djvj]]

In the function nsCoreUtils::IsRootDocument (https://searchfox.org/mozilla-central/source/accessible/base/nsCoreUtils.cpp#341):

This function checks if a document is a root document by getting its docshell tree-item, then obtaining its in-process parent, and checking if the parent is null.

Post-fission, this will return true incorrectly when the parent is out of process. This function should be modified as follows:

1. Obtain the parent.
2. If the parent is non-null, return false, as this document cannot be the root.
3. If the parent is null, then use the associated BrowsingContext to determine whether there is an out-of-process parent, and return true if so, otherwise false.

Comment 1

[Hiroyuki Ikezoe (:hiro)]

I was also thinking that returning true for the out-of-process document is wrong, but after some more reading the code around its call site, now I think returning true looks correct.

There is only one call site of nsCoreUtils::IsRootDocument, which is in DocManager::CreateDocOrRootAccessible. If we consider a given document is not root, we try to get the parent accessible document, then we call BindChildDocument. Apparently it won't work in fission.

So, I think we should rename nsCoreUtils::IsRootDocument to nsCoreUtils::IsRootDocumentInProcess, and make the function return true in the case where the given document is the root document of the out-of-process document tree.

Comment 2

[Chris Peterson [:cpeterson]]

Kannan says replacing nsIDocShellTreeItem calls should block enabling Fission in Nightly (M6).

Comment 3

[James Teh [:Jamie]]

Comment 1 is correct. As far as the a11y engine is concerned, root accessible means in-process root accessible (the outer most accessible in the in-process a11y tree).