[gtritchie]

Axe reports two problems in CellTree, seen in RStudio's Connections pane object browser. Addresses rstudio/rstudio#19244.

• Nested tree items have no group parent (aria-required-parent). Each CellTreeNodeView element has role="treeitem" and renders its children inside itself, through an animation frame, a content container and a child container, none of which has a role. A nested item's closest ancestor with a role is therefore its parent treeitem. Top-level items pass because the CellTree element has role="tree".
• The open/closed/loading images have no alt text (image-alt). CellTree.getImageHtml() builds them with AbstractImagePrototype, which emits an <img> with no alt.

Changes

• CellTreeNodeView.ensureChildContainer() gives the child container role="group" for every node except the root. This produces treeitem > group > treeitem, as in the APG tree pattern. The root's children stay direct descendants of the role="tree" element. The group holds only child items: the empty message and the "show more" link are siblings of the child container in the content container.
• The imageWrapper template, which wraps all three images, gets aria-hidden="true". The item's aria-expanded already conveys the open/closed state. Leaf items render a separate placeholder <div> with no image and are unchanged.

Testing

New tests in CellTreeTest, both of which failed before the change:

• testChildContainerRoles: a top-level item's closest ancestor with a role is the tree. Every nested item, down to a leaf, is in a group whose closest ancestor with a role is its parent item.
• testExpandImagesHiddenFromAssistiveTech: the image wrapper is aria-hidden for an open item, a closed item, an item closed again after being opened, and the loading image.

Results:

• CellTreeTest and AnimatedCellTreeTest pass in HtmlUnit (48 tests).
• checkstyle passes, and ant clean dist-dev builds.
• With RStudio built against this SDK, Axe reports no violations in the Connections pane object browser expanded down to table columns. Before the change, it reported aria-required-parent on every nested item and image-alt on every arrow.

RStudio needs no code change for this: the fix ships when RStudio's GWT_VERSION moves to the release that contains it.

[gtritchie]

No blocking issues. The change fixes both violations it targets, and I found no regressions.

I checked this by building HTML copies of the CellTree DOM before and after the change and running axe-core 4.13 and Chromium's accessibility tree on them. Before the change, axe reports aria-required-parent on nested items and image-alt on the expand images. After the change, it reports neither.

Remaining issues, both of which predate this PR:

• The top-level "Show more" link is a direct child of role="tree". The root node's anchor is in the root's content container, so the tree element owns it directly. When the link is visible, axe reports aria-required-children ("Element has children which are not allowed: a"). The same link inside a nested item passes. In RStudio this only happens when the object browser has more than 512 top-level items (ObjectBrowser sets that page size), so it is rare. Fixing it means moving the link out of the tree element or giving it a role the tree allows, which is outside the scope of this PR. Worth an issue if anyone reports it.
• The "No data" message is part of the nested item's accessible name. It is a sibling of the new group inside the treeitem, so Chromium names an open, empty nested item "emptyTable No data". This PR improves naming overall: before it, every item's name included the text of all its descendants (e.g. "schema table1 col1 loadingTable"). The new group stops that everywhere except for this message.

Optional:

• testChildContainerRoles covers only the first open. The code keeps role="group" after a redraw (loadChildState copies savedChild.childContainer) and after a close followed by a reopen (ensureChildContainer reuses the container), but no test asserts either.

LGTM.