Bug 316344

Summary: [Site Isolation] Enable MultiProcessBackForwardCache in WebKitTestRunner when Site Isolation is enabled
Product: WebKit Reporter: Basuke Suzuki <basuke>
Component: Tools / TestsAssignee: Basuke Suzuki <basuke>
Status: RESOLVED FIXED    
Severity: Normal CC: webkit-bug-importer
Priority: P2 Keywords: InRadar
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   

Basuke Suzuki
Reported 2026-06-04 14:41:04 PDT
Under Site Isolation, WebProcessPool::createWebPage auto-enables MultiProcessBackForwardCache (and UseUIProcessForBackForwardItemLoading) at page creation. WebKitTestRunner applies a full preference set per test (resetPreferencesToConsistentValues -> WKPreferencesResetTestRunnerOverrides), resetting unspecified preferences to their defaults and clobbering that runtime flip. As a result, BFCache-under-Site-Isolation layout tests run with MultiProcessBackForwardCacheEnabled=false, so BackForwardCache::addIfCacheable's guard (siteIsolationEnabled() && !multiProcessBackForwardCacheEnabled()) rejects caching and back/forward restore fails (e.g. fast/events/event-timing-back-forward-cache-duration.html under the mac-site-isolation suite). Mirror the product coupling in WebKitTestRunner: when SiteIsolationEnabled is set, also enable MultiProcessBackForwardCacheEnabled. Add a same-origin Site-Isolation copy of the event-timing test as a regression guard. UseUIProcessForBackForwardItemLoading coupling is deferred; enabling it surfaces a separate nested-frame form-state restoration failure.
Attachments
Basuke Suzuki
Comment 1 2026-06-04 14:49:51 PDT
Basuke Suzuki
Comment 2 2026-06-04 14:50:11 PDT
EWS
Comment 3 2026-06-04 16:25:45 PDT
Committed 314591@main (49a03a1fa5d5): <https://commits.webkit.org/314591@main> Reviewed commits have been landed. Closing PR #66491 and removing active labels.
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