constellation: Track top-level pipeline changes in webviews#43013
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delan merged 1 commit intoservo:mainfrom Mar 6, 2026
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constellation: Track top-level pipeline changes in webviews#43013delan merged 1 commit intoservo:mainfrom
delan merged 1 commit intoservo:mainfrom
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Co-authored-by: Alice Boxhall <[email protected]> Signed-off-by: delan azabani <[email protected]>
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in #43029, we defined an accessibility tree for each webview. we create those trees when accessibility is activated for that webview, then the embedder can graft it into their main accessibility tree. at the time, this accessibility tree was empty, but we ultimately want it to contain the accessibility tree of the documents loaded in the webview at any given time. to do that, we need to graft the active top-level pipeline’s accessibility tree into the webview accessibility tree. we should be able to ignore nested documents inside iframes here, and leave it to their parent documents to graft those in as part of layout accessibility. this patch hooks into the moment in the constellation where we detect that the top-level document has changed (#43013), and notifies libservo of the new AccessKit TreeId for the webview-to-pipeline graft node. this moment covers navigating to a new top-level document and navigating back or forward, but not the initial document loaded in the webview, so we also hook into the moment a ConstellationWebView is created, and do the same for that initial document. now the accessibility tree for a webview with accessibility activated should look like this: - embedder’s main tree - graft node for webview tree → webview tree - ~~graft node for document back in history~~ - graft node for active top-level document → (nothing yet) - ~~graft node for document forward in history~~ Testing: this patch updates the relevant accessibility test in libservo Fixes: part of #4344, extracted from our work in #42338 --------- Signed-off-by: Alice Boxhall <[email protected]> Signed-off-by: delan azabani <[email protected]> Co-authored-by: Alice Boxhall <[email protected]>
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whenever a browsing context loads a new document or otherwise navigates, the constellation sends a new frame tree to the compositor, giving us a nice, relatively central way to detect when we may need to update the graft node in a webview’s AccessKit subtree. but we only want to update that graft node when the pipeline in its top-level browsing context has changed, not just when the pipeline in any of its browsing contexts has changed.
this patch adds a field to the ConstellationWebView that tracks the active top-level pipeline for each webview, allowing us to check when a set_frame_tree_for_webview() call actually involves navigation in the top-level browsing context.
Testing: will be covered by accessibility tree tests in a later patch
Fixes: part of #4344, extracted from our work in #42338