Implement margin-trim for flexbox.

[sammygill]

0efe67f

Implement margin-trim for flexbox.
https://bugs.webkit.org/show_bug.cgi?id=249208
rdar://103285847

Reviewed by Alan Baradlay.

Adds support for the margin-trim property on flexbox containers.
Depending on the values that are set for this property, it will trim
the corresponding edges of the flex items that are adjacent to those
edges of the container.

In order to achieve this, a new data structure, m_marginTrimItems, was
added to RenderFlexibleBox. This structure simply holds the items that
are trimmed according to their location in the flexbox.

The first step of this algorithm is to trim the edges of the first and
last child of the flexbox. This is done so that
RenderFlexibleBox::computeIntrinsicLogicalWidths does not incorrectly
take these margins into consideration when computing the width of the
flexbox under a min/max content constraint.

In order to figure out which items are actually being trimmed, we cannot
perform any trimming until the flex lines are created. As the lines
get created in FlexLayoutAlgorithm::computeNextFlexLine, we can trim the
main axis margins of the first and last items. This will require not
only updating the object's MarginBox but also the main axis sizing
information of the flex item itself. In order to do this, we need to
make FlexItem's mainAxisMargin mutable.

After the line has been constructed, we can trim the cross axis margins
of the items if the line is either the first line or last line of the
flexbox.

* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-block-end-trimmed-only-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-block-end-trimmed-only.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-block-start-trimmed-only-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-block-start-trimmed-only.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-block-trimmed-only-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-block-trimmed-only.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-block-multiline-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-block-multiline.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-grow-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-grow.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-inline-multiline-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-inline-multiline.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-orthogonal-item-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-orthogonal-item.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-shrink-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-column-shrink.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-inline-end-trimmed-only-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-inline-end-trimmed-only.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-inline-start-trimmed-only-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-inline-start-trimmed-only.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-inline-trimmed-only-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-inline-trimmed-only.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-block-multiline-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-block-multiline.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-grow-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-grow.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-inline-multiline-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-inline-multiline.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-orthogonal-item-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-orthogonal-item.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-shrink-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-row-shrink.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-trim-all-margins-expected.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-trim-all-margins.html: Added.
* LayoutTests/platform/mac/imported/w3c/web-platform-tests/css/css-box/margin-trim/flex-template-expected.txt: Added.
* Source/WebCore/rendering/FlexibleBoxAlgorithm.cpp:
(WebCore::FlexLayoutAlgorithm::FlexLayoutAlgorithm):
(WebCore::FlexLayoutAlgorithm::canFitItemWithTrimmedMarginEnd const):
(WebCore::FlexLayoutAlgorithm::removeMarginEndFromFlexSizes const):
(WebCore::FlexLayoutAlgorithm::computeNextFlexLine):
* Source/WebCore/rendering/FlexibleBoxAlgorithm.h:
(WebCore::FlexLayoutAlgorithm::isMultiline const):
* Source/WebCore/rendering/RenderBlock.cpp:
(WebCore::RenderBlock::marginIntrinsicLogicalWidthForChild const):
* Source/WebCore/rendering/RenderBox.cpp:
(WebCore::RenderBox::computeLogicalWidthInFragment const):
(WebCore::RenderBox::fillAvailableMeasure const):
(WebCore::RenderBox::computeOrTrimInlineMargin const):
(WebCore::RenderBox::computeInlineDirectionMargins const):
* Source/WebCore/rendering/RenderBox.h:
* Source/WebCore/rendering/RenderFlexibleBox.cpp:
(WebCore::RenderFlexibleBox::layoutBlock):
(WebCore::RenderFlexibleBox::initializeMarginTrimState):
(WebCore::RenderFlexibleBox::shouldTrimChildMargin const):
(WebCore::RenderFlexibleBox::shouldTrimMainAxisMarginStart const):
(WebCore::RenderFlexibleBox::shouldTrimMainAxisMarginEnd const):
(WebCore::RenderFlexibleBox::shouldTrimCrossAxisMarginStart const):
(WebCore::RenderFlexibleBox::shouldTrimCrossAxisMarginEnd const):
(WebCore::RenderFlexibleBox::trimMainAxisMarginStart):
(WebCore::RenderFlexibleBox::trimMainAxisMarginEnd):
(WebCore::RenderFlexibleBox::trimCrossAxisMarginStart):
(WebCore::RenderFlexibleBox::trimCrossAxisMarginEnd):
(WebCore::RenderFlexibleBox::layoutFlexItems):
* Source/WebCore/rendering/RenderFlexibleBox.h:

Canonical link: https://commits.webkit.org/258563@main

1a9552c

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[alanbaradlay]

rs=me
it would be great if someone with more extensive flex + margin knowledge could also take a look at it.

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	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🛠 gtk	🛠 wincairo
✅ 🧪 webkitperl	🧪 ios-wk2	🧪 api-mac	🧪 gtk-wk2
	🧪 api-ios	🧪 mac-wk1	🧪 api-gtk
	🛠 tv	✅ 🧪 mac-wk2
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Committed 258563@main (0efe67f): https://commits.webkit.org/258563@main

Reviewed commits have been landed. Closing PR #8166 and removing active labels.