layout: Preserve boxes in rebuilt subtrees underneath independent formatting contexts by mrobinson · Pull Request #42582 · servo/servo

mrobinson · 2026-02-12T15:19:23Z

When a box needs to be rebuilt due to a style change, it previously
would rebuild the entire box subtree, including all descendants. This is
probably unnecessary when crossing independent formatting context
boundaries. This change limits box tree damage pushed downward when
entering certain types of independent formatting contexts. The types can
be expanded later, but this is just a first conservative step. This is
necessary in order to start preserving fragments in these subtrees.

Testing: This should not change observable layout behavior. We do not really
have tests to verify these kind of optimizations.

…matting contexts When a box needs to be rebuilt due to a style change, it previously would rebuild the entire box subtree, including all descendants. This is probably unnecessary when crossing independent formatting context boundaries. This change limits box tree damage pushed downward when entering certain types of independent formatting contexts. The types can be expanded later, but this is just a first conservative step. This is necessary in order to start preserving fragments in these subtrees. Signed-off-by: Martin Robinson <mrobinson@igalia.com> Co-authored-by: Oriol Brufau <obrufau@igalia.com> Co-authored-by: Luke Warlow <lwarlow@igalia.com>

github-actions · 2026-02-12T15:20:30Z

🔨 Triggering try run (#21952571340) for Linux (WPT)

github-actions · 2026-02-12T15:52:54Z

Test results for linux-wpt from try job (#21952571340):

Flaky unexpected result (33)

OK /FileAPI/url/url-with-fetch.any.worker.html (#21517)
- FAIL [expected PASS] subtest: Revoke blob URL after calling fetch, fetch should succeed
```
promise_test: Unhandled rejection with value: object "TypeError: Network error: Blob URL store error: InvalidFileID"
```
ERROR [expected OK] /IndexedDB/cursor-overloads.any.html (#42437)
OK [expected ERROR] /IndexedDB/cursor-overloads.any.worker.html (#42324)
OK /IndexedDB/transaction-deactivation-timing.any.html (#38772)
- PASS [expected FAIL] subtest: New transactions are deactivated before next task
- PASS [expected FAIL] subtest: New transactions from microtask are deactivated before next task

OK /_mozilla/css/offset_properties_inline.html (#40543)

FAIL [expected PASS] subtest: offsetTop

assert_equals: offsetTop of #inline-1 should be 0. expected 0 but got -1

FAIL [expected PASS] subtest: offsetLeft

assert_equals: offsetLeft of #inline-2 should be 40. expected 40 but got 25

OK /_mozilla/mozilla/getBoundingClientRect.html (#39668)
- FAIL [expected PASS] subtest: getBoundingClientRect 1
```
assert_equals: expected 62 but got 60.35
```
TIMEOUT [expected OK] /credential-management/credentialscontainer-frame-basics.https.html (#39430)
- TIMEOUT [expected FAIL] subtest: navigator.credentials should be undefined in documents generated from data: URLs.
```
Test timed out
```
FAIL [expected PASS] /css/css-backgrounds/border-image-repeat-space-9.html
OK /css/css-fonts/generic-family-keywords-002.html (#40929)
- FAIL [expected PASS] subtest: font-family: -webkit-serif treated as <font-family>, not <generic-name>
```
assert_equals: expected 30 but got 50
```
- FAIL [expected PASS] subtest: font-family: -webkit-sans-serif treated as <font-family>, not <generic-name>
```
assert_equals: expected 30 but got 50
```
- FAIL [expected PASS] subtest: font-family: -webkit-cursive treated as <font-family>, not <generic-name>
```
assert_equals: expected 30 but got 50
```
- FAIL [expected PASS] subtest: font-family: -webkit-fantasy treated as <font-family>, not <generic-name>
```
assert_equals: expected 30 but got 50
```
- FAIL [expected PASS] subtest: font-family: -webkit-monospace treated as <font-family>, not <generic-name>
```
assert_equals: expected 30 but got 50
```
- FAIL [expected PASS] subtest: font-family: -webkit-system-ui treated as <font-family>, not <generic-name>
```
assert_equals: expected 30 but got 50
```
- FAIL [expected PASS] subtest: font-family: -webkit-math treated as <font-family>, not <generic-name>
```
assert_equals: expected 30 but got 50
```
- PASS [expected FAIL] subtest: font-family: -webkit-generic(fangsong) treated as <font-family>, not <generic-name>
- PASS [expected FAIL] subtest: font-family: -webkit-generic(kai) treated as <font-family>, not <generic-name>
- PASS [expected FAIL] subtest: font-family: -webkit-generic(khmer-mul) treated as <font-family>, not <generic-name>
- And 12 more unexpected results...
OK /css/css-fonts/generic-family-keywords-003.html (#38994)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted fantasy (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted monospace (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted system-ui (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted math (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted generic(fangsong) (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted generic(khmer-mul) (drawing text in a canvas)
- PASS [expected FAIL] subtest: @font-face matching for quoted and unquoted generic(nastaliq) (drawing text in a canvas)
TIMEOUT [expected OK] /fetch/api/redirect/redirect-keepalive.https.any.html (#32153)
- TIMEOUT [expected PASS] subtest: [keepalive][iframe][load] mixed content redirect; setting up
```
Test timed out
```
TIMEOUT /fetch/metadata/generated/css-images.https.sub.tentative.html (#42229)
- PASS [expected FAIL] subtest: content sec-fetch-site - Same-Origin -> Same Origin
ERROR /fetch/metadata/generated/serviceworker.https.sub.html (#36247)
- FAIL [expected PASS] subtest: sec-fetch-site - Same origin, no options - registration
```
promise_test: Unhandled rejection with value: object "Error: Failed to query for recorded headers."
```
OK /fetch/metadata/window-open.https.sub.html (#40339)
- FAIL [expected PASS] subtest: Same-site window, forced, reloaded
```
The operation is insecure.
```
ERROR [expected OK] /focus/focus-event-after-switching-iframes.sub.html (#40368)
OK /html/browsers/browsing-the-web/navigating-across-documents/005.html (#27062)
- PASS [expected FAIL] subtest: Link with onclick navigation and href navigation
OK /html/browsers/browsing-the-web/navigating-across-documents/navigation-unload-same-origin.window.html (#29049)
- PASS [expected FAIL] subtest: Same-origin navigation started from unload handler must be ignored
OK /html/browsers/history/the-history-interface/traverse_the_history_2.html (#21383)
- PASS [expected FAIL] subtest: Multiple history traversals, last would be aborted
TIMEOUT /html/semantics/embedded-content/media-elements/autoplay-disabled-by-feature-policy.https.sub.html (#41221)
- TIMEOUT [expected FAIL] subtest: Feature-Policy header: autoplay "none" disallows same-origin iframes.
```
Test timed out
```
OK [expected TIMEOUT] /html/semantics/embedded-content/media-elements/src_object_blob.html (#40340)
- PASS [expected TIMEOUT] subtest: HTMLMediaElement.srcObject blob
TIMEOUT [expected OK] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_navigate_other_frame_popup.sub.html (#39702)
- TIMEOUT [expected FAIL] subtest: Sandboxed iframe can not navigate other frame's popup
```
Test timed out
```
OK /html/semantics/forms/form-submission-0/jsurl-form-submit.tentative.html (#36489)
- PASS [expected FAIL] subtest: Verifies that form submissions scheduled inside javascript: urls take precedence over the javascript: url's return value.

OK /html/webappapis/user-prompts/print-during-unload.html (#35944)

FAIL [expected PASS] subtest: print() during unload

assert_array_equals: expected property 1 to be "destination" but got "error: window.print is not a function" (expected array ["start", "destination"] got ["start", "error: window.print is not a function"])

OK /paint-timing/fcp-only/input-text.html (#42439)
- FAIL [expected PASS] subtest: Text from a form control triggers First Contentful Paint.
```
assert_equals: First contentful paint marked too early.  expected 0 but got 1
```
OK /paint-timing/first-image-child.html (#42455)
- FAIL [expected PASS] subtest: Child iframe ignores paint-timing events fired from parent image rendering.
```
assert_equals: expected "0" but got "1 paint first-paint"
```
PASS [expected FAIL] /png/apng/acTL-plays-one.html (#41218)
OK /resource-timing/buffer-full-add-then-clear.html (#40819)
- FAIL [expected PASS] subtest: Test that if the buffer is cleared after entries were added to the secondary buffer, those entries make it into the primary one
```
assert_equals: Number of entries does not match the expected value. expected 3 but got 0
```
TIMEOUT [expected OK] /trusted-types/trusted-types-navigation.html?01-05 (#38975)
- TIMEOUT [expected PASS] subtest: Navigate a window via anchor with javascript:-urls in report-only mode.
```
Test timed out
```
- NOTRUN [expected PASS] subtest: Navigate a window via anchor with javascript:-urls w/ default policy in report-only mode.
- NOTRUN [expected PASS] subtest: Navigate a frame via anchor with javascript:-urls in enforcing mode.
TIMEOUT /trusted-types/trusted-types-navigation.html?06-10 (#37920)
- TIMEOUT [expected FAIL] subtest: Navigate a frame via anchor with javascript:-urls in report-only mode.
```
Test timed out
```
- NOTRUN [expected TIMEOUT] subtest: Navigate a frame via anchor with javascript:-urls w/ default policy in report-only mode.
OK /webdriver/tests/classic/take_screenshot/iframe.py
- ERROR [expected PASS] subtest: test_always_captures_top_browsing_context
```
setup error: ConnectionRefusedError: [Errno 111] Connection refused
```
- ERROR [expected PASS] subtest: test_source_origin[same_origin]
```
setup error: ConnectionRefusedError: [Errno 111] Connection refused
```
- ERROR [expected PASS] subtest: test_source_origin[cross_origin]
```
setup error: ConnectionRefusedError: [Errno 111] Connection refused
```
OK /webxr/xrSession_features_deviceSupport.https.html (#24357)
- FAIL [expected PASS] subtest: Immersive XRSession requests with no supported device should reject
```
assert_unreached: Should have rejected: undefined Reached unreachable code
```
CRASH [expected OK] /workers/WorkerNavigator_onLine.htm
ERROR [expected OK] /workers/baseurl/alpha/sharedworker-in-worker.html (#21315)

Stable unexpected results that are known to be intermittent (21)

FAIL [expected PASS] /_mozilla/mozilla/sslfail.html (#10760)
TIMEOUT [expected OK] /_mozilla/mozilla/window_resize_event.html (#36741)
- TIMEOUT [expected PASS] subtest: Popup onresize event fires after resizeTo
```
Test timed out
```
CRASH [expected PASS] /_mozilla/shadow-dom/move-element-with-ua-shadow-tree-crash.html (#39473)

OK /_webgl/conformance/textures/misc/texture-upload-size.html (#21770)

FAIL [expected PASS] subtest: WebGL test #45

assert_true: Texture was smaller than the expected size 2x2 expected true got false

FAIL [expected PASS] subtest: WebGL test #47

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : when calling texSubImage2D with the same texture upload with offset 1, 1 expected true got false

FAIL [expected PASS] subtest: WebGL test #49

assert_true: Texture was smaller than the expected size 2x2 expected true got false

FAIL [expected PASS] subtest: WebGL test #51

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : when calling texSubImage2D with the same texture upload with offset 1, 1 expected true got false

PASS [expected FAIL] subtest: WebGL test #53
PASS [expected FAIL] subtest: WebGL test #55
PASS [expected FAIL] subtest: WebGL test #57
PASS [expected FAIL] subtest: WebGL test #59

FAIL [expected PASS] subtest: WebGL test #61

assert_true: Texture was smaller than the expected size 2x2 expected true got false

FAIL [expected PASS] subtest: WebGL test #63

assert_true: getError expected: INVALID_VALUE. Was NO_ERROR : when calling texSubImage2D with the same texture upload with offset 1, 1 expected true got false

And 6 more unexpected results...

OK /css/css-cascade/layer-font-face-override.html (#35935)
- FAIL [expected PASS] subtest: @font-face override update with appended sheet 2
```
assert_equals: expected "80px" but got "38.3166666666667px"
```
OK /css/css-fonts/generic-family-keywords-001.html (#37467)
- FAIL [expected PASS] subtest: @font-face matching for quoted and unquoted generic(kai)
```
assert_equals: quoted generic(kai) matches  @font-face rule expected 30 but got 50
```
- FAIL [expected PASS] subtest: @font-face matching for quoted and unquoted generic(nastaliq)
```
assert_equals: quoted generic(nastaliq) matches  @font-face rule expected 30 but got 50
```
ERROR [expected OK] /fetch/fetch-later/quota/same-origin-iframe/multiple-iframes.https.window.html (#35176)
OK /fetch/metadata/generated/css-font-face.https.sub.tentative.html (#32732)
- FAIL [expected PASS] subtest: sec-fetch-mode
```
promise_test: Unhandled rejection with value: object "Error: Failed to query for recorded headers."
```
OK /fetch/metadata/generated/css-font-face.sub.tentative.html (#34624)
- PASS [expected FAIL] subtest: sec-fetch-storage-access - Not sent to non-trustworthy same-origin destination
- FAIL [expected PASS] subtest: sec-fetch-storage-access - Not sent to non-trustworthy cross-site destination
```
promise_test: Unhandled rejection with value: object "Error: Failed to query for recorded headers."
```
TIMEOUT /fetch/metadata/generated/css-images.sub.tentative.html (#29047)
- PASS [expected TIMEOUT] subtest: background-image sec-fetch-mode - Not sent to non-trustworthy same-site destination

OK /html/browsers/browsing-the-web/navigating-across-documents/refresh/same-document-refresh.html (#34597)

FAIL [expected PASS] subtest: Same-Document Referrer from Refresh

assert_equals: original page loads expected "http://web-platform.test:8000/html/browsers/browsing-the-web/navigating-across-documents/refresh/resources/refresh-with-section.sub.html?url=%23section" but got "http://web-platform.test:8000/html/browsers/browsing-the-web/navigating-across-documents/refresh/resources/refresh-with-section.sub.html?url=%23section#section"

OK /html/browsers/history/the-history-interface/traverse_the_history_4.html (#21383)
- FAIL [expected PASS] subtest: Multiple history traversals, last would be aborted
```
assert_array_equals: Pages opened during history navigation expected property 1 to be 5 but got 3 (expected array [6, 5] got [6, 3])
```

OK [expected TIMEOUT] /html/interaction/focus/the-autofocus-attribute/supported-elements.html (#24145)

FAIL [expected NOTRUN] subtest: Host element with delegatesFocus should support autofocus

assert_equals: expected Element node &lt;div autofocus=""&gt;&lt;/div&gt; but got Element node &lt;body&gt;&lt;div autofocus=""&gt;&lt;/div&gt;&lt;/body&gt;

FAIL [expected NOTRUN] subtest: Host element with delegatesFocus including no focusable descendants should be skipped

assert_equals: expected Element node &lt;input autofocus=""&gt;&lt;/input&gt; but got Element node &lt;body&gt;&lt;div autofocus=""&gt;&lt;/div&gt;&lt;input autofocus=""&gt;&lt;/body&gt;

FAIL [expected NOTRUN] subtest: Area element should support autofocus

promise_test: Unhandled rejection with value: object "TypeError: can't access property "appendChild", w.document.querySelector(...) is null"

OK [expected TIMEOUT] /html/interaction/focus/the-autofocus-attribute/update-the-rendering.html (#24145)
- FAIL [expected TIMEOUT] subtest: "Flush autofocus candidates" should be happen before a scroll event and animation frame callbacks
```
assert_array_equals: animationFrame lengths differ, expected array ["autofocus", "scroll", "animationFrame"] length 3, got ["animationFrame"] length 1
```
OK /navigation-timing/test-navigation-type-reload.html (#33334)
- FAIL [expected PASS] subtest: Reload domComplete > Original domComplete
```
assert_true: Reload domComplete &gt; Original domComplete expected true got false
```
- FAIL [expected PASS] subtest: Reload domContentLoadedEventEnd > Original domContentLoadedEventEnd
```
assert_true: Reload domContentLoadedEventEnd &gt; Original domContentLoadedEventEnd expected true got false
```
- FAIL [expected PASS] subtest: Reload domInteractive > Original domInteractive
```
assert_true: Reload domInteractive &gt; Original domInteractive expected true got false
```
- FAIL [expected PASS] subtest: Reload loadEventEnd > Original loadEventEnd
```
assert_true: Reload loadEventEnd &gt; Original loadEventEnd expected true got false
```
- FAIL [expected PASS] subtest: Reload loadEventStart > Original loadEventStart
```
assert_true: Reload loadEventStart &gt; Original loadEventStart expected true got false
```
OK /paint-timing/fcp-only/fcp-with-rtl.html (#42357)
- FAIL [expected PASS] subtest: FCP should fire when coordinates are negative, if within document scrollable area
```
assert_equals: First contentful paint marked too early.  expected 0 but got 1
```
OK /pointerevents/compat/pointerevent_touch-action_two-finger_interaction.html (#40418)
- PASS [expected FAIL] subtest: touch two-finger pan on 'touch-action: pan-x pan-y'
OK [expected CRASH] /resource-timing/render-blocking-status-link.html (#41664)
OK [expected TIMEOUT] /trusted-types/trusted-types-navigation.html?31-35 (#38034)
- PASS [expected TIMEOUT] subtest: Navigate a frame via form-submission with javascript:-urls w/ default policy in report-only mode.
- FAIL [expected NOTRUN] subtest: Navigate a window via form-submission with javascript:-urls w/ a default policy throwing an exception in enforcing mode.
```
promise_test: Unhandled rejection with value: "Unexpected message received: \"No securitypolicyviolation reported!\""
```
- FAIL [expected NOTRUN] subtest: Navigate a window via form-submission with javascript:-urls w/ a default policy throwing an exception in report-only mode.
```
promise_test: Unhandled rejection with value: "Unexpected message received: \"No securitypolicyviolation reported!\""
```
- FAIL [expected NOTRUN] subtest: Navigate a window via form-submission with javascript:-urls w/ a default policy making the URL invalid in enforcing mode.
```
promise_test: Unhandled rejection with value: "Unexpected message received: \"No securitypolicyviolation reported!\""
```
OK /visual-viewport/resize-event-order.html (#41981)
- PASS [expected FAIL] subtest: Popup: DOMWindow resize fired before VisualViewport.
OK [expected ERROR] /webxr/render_state_update.https.html (#27535)

github-actions · 2026-02-12T15:53:02Z

✨ Try run (#21952571340) succeeded.

mrobinson requested a review from Loirooriol as a code owner February 12, 2026 15:19

servo-highfive added the S-awaiting-review There is new code that needs to be reviewed. label Feb 12, 2026

Loirooriol added the T-linux-wpt Do a try run of the WPT label Feb 12, 2026

github-actions bot removed the T-linux-wpt Do a try run of the WPT label Feb 12, 2026

Loirooriol approved these changes Feb 12, 2026

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servo-highfive removed the S-awaiting-review There is new code that needs to be reviewed. label Feb 12, 2026

Loirooriol added this pull request to the merge queue Feb 12, 2026

servo-highfive added the S-awaiting-merge The PR is in the process of compiling and running tests on the automated CI. label Feb 12, 2026

Merged via the queue into servo:main with commit 260eb86 Feb 12, 2026
71 checks passed

Loirooriol deleted the try-to-reuse-boxes-in-subtrees branch February 12, 2026 16:55

servo-highfive removed the S-awaiting-merge The PR is in the process of compiling and running tests on the automated CI. label Feb 12, 2026

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layout: Preserve boxes in rebuilt subtrees underneath independent formatting contexts#42582

layout: Preserve boxes in rebuilt subtrees underneath independent formatting contexts#42582
Loirooriol merged 1 commit intoservo:mainfrom
mrobinson:try-to-reuse-boxes-in-subtrees

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