Speculation rules prefetch results are not used for prerendering

[hiroshige-g]

Problem

In a scenario like:

1. Speculation rules prefetch to a URL is added to Document A
2. Speculation rules prerender to the same URL is added to Document A

The prefetched results from Step 1 isn't used for the prerendering navigation request in Step 2.

This is because prefetch records is Document-scoped (assciated with navigable’s active document in https://html.spec.whatwg.org/multipage/browsing-the-web.html#navigate):

Let prefetchRecord be the result of finding a matching prefetch record given navigable’s active document, entry’s URL, and targetSnapshotParams’s sandboxing flags.

but start user-agent initiated prerendering and start referrer-initiated prerendering uses a newly created navigable and thus no prefetch records are there.

• WPT (reflecting the current spec): https://github.com/web-platform-tests/wpt/pull/39241
• Chromium's bug: https://crbug.com/1422815

Possible Solution

Check sourceDocument of https://html.spec.whatwg.org/multipage/browsing-the-web.html#navigate instead of navigable’s active document in the case of prerendering. This would make start referrer-initiated prerendering to use the prefetched results in the scenario above.

[tunetheweb]

This has been fixed in Chrome so can this issue be closed now? Or is there spec updates to be done to make it clear this should be done?