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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/277579">277579</a></dd>
<dt>Author</dt> <dd>ntim@apple.com</dd>
<dt>Date</dt> <dd>2021-05-17 03:09:03 -0700 (Mon, 17 May 2021)</dd>
</dl>

<h3>Log Message</h3>
<pre>will-change: position should not create a containing block for position: fixed elements
https://bugs.webkit.org/show_bug.cgi?id=225443

Reviewed by Antti Koivisto.

This partially undoes <a href="http://trac.webkit.org/projects/webkit/changeset/276627">r276627</a> which made will-change: position create a CB for all out-of-flow elements:

- Removed CSSPropertyPosition from createsContainingBlockForOutOfFlowPositioned() to not create a containing block
for position: fixed; children.
- Added createsContainingBlockForAbsolutelyPositioned() with CSSPropertyPosition to still create a containing block
for position: absolute; children.

Enabled WPT (which covers both cases): css/css-will-change/will-change-fixpos-cb-position-1.html

Source/WebCore:

* rendering/RenderElement.h:
(WebCore::RenderElement::canContainAbsolutelyPositionedObjects const):
* rendering/style/WillChangeData.cpp:
(WebCore::WillChangeData::createsContainingBlockForAbsolutelyPositioned const):
(WebCore::WillChangeData::createsContainingBlockForOutOfFlowPositioned const):
* rendering/style/WillChangeData.h:

LayoutTests:

* TestExpectations:</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsChangeLog">trunk/LayoutTests/ChangeLog</a></li>
<li><a href="#trunkLayoutTestsTestExpectations">trunk/LayoutTests/TestExpectations</a></li>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCorerenderingRenderElementh">trunk/Source/WebCore/rendering/RenderElement.h</a></li>
<li><a href="#trunkSourceWebCorerenderingstyleWillChangeDatacpp">trunk/Source/WebCore/rendering/style/WillChangeData.cpp</a></li>
<li><a href="#trunkSourceWebCorerenderingstyleWillChangeDatah">trunk/Source/WebCore/rendering/style/WillChangeData.h</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkLayoutTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/ChangeLog (277578 => 277579)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/ChangeLog      2021-05-17 08:56:17 UTC (rev 277578)
+++ trunk/LayoutTests/ChangeLog 2021-05-17 10:09:03 UTC (rev 277579)
</span><span class="lines">@@ -1,3 +1,21 @@
</span><ins>+2021-05-17  Tim Nguyen  <ntim@apple.com>
+
+        will-change: position should not create a containing block for position: fixed elements
+        https://bugs.webkit.org/show_bug.cgi?id=225443
+
+        Reviewed by Antti Koivisto.
+
+        This partially undoes r276627 which made will-change: position create a CB for all out-of-flow elements:
+
+        - Removed CSSPropertyPosition from createsContainingBlockForOutOfFlowPositioned() to not create a containing block
+        for position: fixed; children.
+        - Added createsContainingBlockForAbsolutelyPositioned() with CSSPropertyPosition to still create a containing block
+        for position: absolute; children.
+
+        Enabled WPT (which covers both cases): css/css-will-change/will-change-fixpos-cb-position-1.html
+
+        * TestExpectations:
+
</ins><span class="cx"> 2021-05-16  Cameron McCormack  <heycam@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Make MathML WPTs wait for all font loads
</span></span></pre></div>
<a id="trunkLayoutTestsTestExpectations"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/TestExpectations (277578 => 277579)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/TestExpectations       2021-05-17 08:56:17 UTC (rev 277578)
+++ trunk/LayoutTests/TestExpectations  2021-05-17 10:09:03 UTC (rev 277579)
</span><span class="lines">@@ -4857,7 +4857,6 @@
</span><span class="cx"> webkit.org/b/225035 imported/w3c/web-platform-tests/css/css-will-change/will-change-fixedpos-cb-002.html [ ImageOnlyFailure ]
</span><span class="cx"> webkit.org/b/225034 imported/w3c/web-platform-tests/css/css-will-change/will-change-fixedpos-cb-003.html [ ImageOnlyFailure ]
</span><span class="cx"> webkit.org/b/225442 imported/w3c/web-platform-tests/css/css-will-change/will-change-fixpos-cb-contain-1.html [ ImageOnlyFailure ]
</span><del>-webkit.org/b/225443 imported/w3c/web-platform-tests/css/css-will-change/will-change-fixpos-cb-position-1.html [ ImageOnlyFailure ]
</del><span class="cx"> webkit.org/b/224902 [ Debug ] imported/w3c/web-platform-tests/css/css-will-change/parsing/will-change-invalid.html [ Skip ]
</span><span class="cx"> 
</span><span class="cx"> # Implement offset-* properties
</span></span></pre></div>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (277578 => 277579)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog   2021-05-17 08:56:17 UTC (rev 277578)
+++ trunk/Source/WebCore/ChangeLog      2021-05-17 10:09:03 UTC (rev 277579)
</span><span class="lines">@@ -1,3 +1,26 @@
</span><ins>+2021-05-17  Tim Nguyen  <ntim@apple.com>
+
+        will-change: position should not create a containing block for position: fixed elements
+        https://bugs.webkit.org/show_bug.cgi?id=225443
+
+        Reviewed by Antti Koivisto.
+
+        This partially undoes r276627 which made will-change: position create a CB for all out-of-flow elements:
+
+        - Removed CSSPropertyPosition from createsContainingBlockForOutOfFlowPositioned() to not create a containing block
+        for position: fixed; children.
+        - Added createsContainingBlockForAbsolutelyPositioned() with CSSPropertyPosition to still create a containing block
+        for position: absolute; children.
+
+        Enabled WPT (which covers both cases): css/css-will-change/will-change-fixpos-cb-position-1.html
+
+        * rendering/RenderElement.h:
+        (WebCore::RenderElement::canContainAbsolutelyPositionedObjects const):
+        * rendering/style/WillChangeData.cpp:
+        (WebCore::WillChangeData::createsContainingBlockForAbsolutelyPositioned const):
+        (WebCore::WillChangeData::createsContainingBlockForOutOfFlowPositioned const):
+        * rendering/style/WillChangeData.h:
+
</ins><span class="cx"> 2021-05-17  Zan Dobersek  <zdobersek@igalia.com>
</span><span class="cx"> 
</span><span class="cx">         REGRESSION(r277560): conditional attribute typos in IDLs for OffscreenCanvas, OffscreenCanvasRenderingContext2D
</span></span></pre></div>
<a id="trunkSourceWebCorerenderingRenderElementh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderElement.h (277578 => 277579)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/rendering/RenderElement.h   2021-05-17 08:56:17 UTC (rev 277578)
+++ trunk/Source/WebCore/rendering/RenderElement.h      2021-05-17 10:09:03 UTC (rev 277579)
</span><span class="lines">@@ -449,7 +449,7 @@
</span><span class="cx">     return style().position() != PositionType::Static
</span><span class="cx">         || (isRenderBlock() && hasTransformRelatedProperty())
</span><span class="cx">         // FIXME: will-change should create containing blocks on inline boxes (bug 225035)
</span><del>-        || (isRenderBlock() && style().willChange() && style().willChange()->createsContainingBlockForOutOfFlowPositioned())
</del><ins>+        || (isRenderBlock() && style().willChange() && style().willChange()->createsContainingBlockForAbsolutelyPositioned())
</ins><span class="cx">         || isSVGForeignObject()
</span><span class="cx">         || shouldApplyLayoutContainment(*this)
</span><span class="cx">         || isRenderView();
</span></span></pre></div>
<a id="trunkSourceWebCorerenderingstyleWillChangeDatacpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/style/WillChangeData.cpp (277578 => 277579)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/rendering/style/WillChangeData.cpp  2021-05-17 08:56:17 UTC (rev 277578)
+++ trunk/Source/WebCore/rendering/style/WillChangeData.cpp     2021-05-17 10:09:03 UTC (rev 277579)
</span><span class="lines">@@ -60,10 +60,15 @@
</span><span class="cx">     return false;
</span><span class="cx"> }
</span><span class="cx"> 
</span><ins>+bool WillChangeData::createsContainingBlockForAbsolutelyPositioned() const
+{
+    return createsContainingBlockForOutOfFlowPositioned()
+        || containsProperty(CSSPropertyPosition);
+}
+
</ins><span class="cx"> bool WillChangeData::createsContainingBlockForOutOfFlowPositioned() const
</span><span class="cx"> {
</span><del>-    return containsProperty(CSSPropertyPosition)
-        || containsProperty(CSSPropertyPerspective)
</del><ins>+    return containsProperty(CSSPropertyPerspective)
</ins><span class="cx">         // CSS transforms
</span><span class="cx">         || containsProperty(CSSPropertyTransform)
</span><span class="cx">         || containsProperty(CSSPropertyTransformStyle)
</span></span></pre></div>
<a id="trunkSourceWebCorerenderingstyleWillChangeDatah"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/style/WillChangeData.h (277578 => 277579)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/rendering/style/WillChangeData.h    2021-05-17 08:56:17 UTC (rev 277578)
+++ trunk/Source/WebCore/rendering/style/WillChangeData.h       2021-05-17 10:09:03 UTC (rev 277579)
</span><span class="lines">@@ -52,6 +52,7 @@
</span><span class="cx">     bool containsContents() const;
</span><span class="cx">     bool containsProperty(CSSPropertyID) const;
</span><span class="cx"> 
</span><ins>+    bool createsContainingBlockForAbsolutelyPositioned() const;
</ins><span class="cx">     bool createsContainingBlockForOutOfFlowPositioned() const;
</span><span class="cx">     bool canCreateStackingContext() const { return m_canCreateStackingContext; }
</span><span class="cx">     bool canTriggerCompositing() const { return m_canTriggerCompositing; }
</span></span></pre>
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