feat(roleHelpers): compute tree implicit arialevel

[MatanBobi]

What: Adding the option to implicitly get the aria-level of a treeitem

Why: Resolves #980

How: At the moment, I'm using the naive approach and climb up the tree until I reach a node with explicit role tree.

This isn't ready yet, it's just a draft to see if this approach looks good.

Checklist:

• Documentation added to the
  docs site
• Tests
• TypeScript definitions updated
• Ready to be merged
  

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Sandbox	Source
react-testing-library-examples	Configuration
react-testing-library aria-role tree	Issue #980

[eps1lon]

Should I review this considering it's in draft and you said it's not ready yet?

[cmorten]

At the moment, I'm using the naive approach and climb up the tree until I reach a node with explicit role tree.

Some care needed here (if this is picked up again) as the implicit level (if I’m interpreting correctly) is not necessarily the depth in the DOM tree, but rather the depth in the accessibility tree from the parent node (including concepts such as aria-owns), though aria simply says "document structure" so maybe it’s ambiguous.

The core aam spec I think clarifies this: "If aria-level is not provided or inherited for an element of role treeitem or comment, user agents implementing IAccessible2 or ATK/AT-SPI MUST compute it by following the explicit or computed RELATION_NODE_CHILD_OF relations."

In the majority of cases this is likely equivalent, but there are patterns where application of role="presentation" or role="none" complicates things, e.g. see https://www.w3.org/WAI/ARIA/apg/patterns/treeview/examples/treeview-navigation/, or where using groups adds extra DOM hierarchy that need be ignored, e.g. see https://www.w3.org/WAI/ARIA/apg/patterns/treeview/examples/treeview-1a/

Adding the option to implicitly get the aria-level of a treeitem

Worth considering listitem, row (but only when in a treegrid), and comment (but only if want to support wai-aria 1.3 which is draft atm) for this as they too have implicit levels.

REF:

• https://www.w3.org/TR/wai-aria-1.2/#aria-level
• https://www.w3.org/TR/core-aam-1.2/#mapping_additional_position

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Update: on re-read of the implementation, I think this might be all ok (and my concerns r.e. nested already mitigated by the implementation), apologies should read properly first and comment later.

Comment r.e. other roles stands, and suspect would be good to add the more complex nesting examples as test cases.