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css: drop the logical longhands a 4-side margin/padding shorthand overrides instead of flushing them #38576

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css: drop the logical longhands a 4-side margin/padding shorthand overrides instead of flushing them #38576

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1a34d26
css: drop the logical longhands a 4-side shorthand overrides instead …
robobun Aug 14, 2026
af75afd
css: keep every buffered side when a target rejects any side of the s…
robobun Aug 14, 2026
ad4497d
css: shorten the shorthand arm comment
robobun Aug 14, 2026
55ffa5d
css: single-line comments in the shorthand arm
robobun Aug 14, 2026
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46 changes: 18 additions & 28 deletions src/css/properties/margin_padding.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -676,42 +676,32 @@ impl<S: SizeHandlerSpec> SizeHandler<S> {
);
} else if tag == S::SHORTHAND {
let val = S::extract_shorthand(property);
self.flush_helper_physical(
PhysicalSlot::Top,
S::shorthand_top(val),
S::SHORTHAND_CATEGORY,
dest,
context,
);
self.flush_helper_physical(
PhysicalSlot::Right,
S::shorthand_right(val),
S::SHORTHAND_CATEGORY,
dest,
context,
);
self.flush_helper_physical(
PhysicalSlot::Bottom,
S::shorthand_bottom(val),
S::SHORTHAND_CATEGORY,
dest,
context,
);
self.flush_helper_physical(
PhysicalSlot::Left,
S::shorthand_left(val),
S::SHORTHAND_CATEGORY,
dest,
context,
);

// The buffered values are only live for a target that rejects the whole declaration.
if let Some(browsers) = context.targets.browsers {
let rejected_by_a_target = [
S::shorthand_top(val),
S::shorthand_right(val),
S::shorthand_bottom(val),
S::shorthand_left(val),
]
.into_iter()
.any(|v| !v.is_compatible(&browsers));
if rejected_by_a_target {
self.flush(dest, context);
}
}

self.top = Some(S::shorthand_top(val).clone());
self.right = Some(S::shorthand_right(val).clone());
self.bottom = Some(S::shorthand_bottom(val).clone());
self.left = Some(S::shorthand_left(val).clone());
// Dead in every writing mode; flushing would put compiled inline ones after this rule.
self.block_start = None;
self.block_end = None;
self.inline_start = None;
self.inline_end = None;
self.category = S::SHORTHAND_CATEGORY;
self.has_any = true;
} else {
return false;
Expand Down
133 changes: 133 additions & 0 deletions test/js/bun/css/css.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2436,6 +2436,139 @@ describe("css tests", () => {
);
});

// A 4-side shorthand sets all four physical sides, so logical longhands declared before it in the
// same rule are dead in every writing mode. They must not survive into the output: when logical
// properties are compiled for old targets, inline longhands become separate :lang() rules emitted
// after the rule, which would win over the shorthand. The one reason to keep anything declared
// before the shorthand is a target that rejects the shorthand's value.
describe("logical longhands overridden by a 4-side shorthand", () => {
for (const [shorthand, inlineStart, inlineEnd, inline, blockStart, top] of [
["margin", "margin-inline-start", "margin-inline-end", "margin-inline", "margin-block-start", "margin-top"],
["padding", "padding-inline-start", "padding-inline-end", "padding-inline", "padding-block-start", "padding-top"],
]) {
// Safari 8 compiles logical properties away (the :lang() cases above use it too); Safari 15
// supports them.
for (const [label, targets] of [
["logical properties compiled", { safari: 8 << 16 }],
["logical properties supported", { safari: 15 << 16 }],
] as const) {
describe(`${shorthand}, ${label}`, () => {
for (const decls of [
`${inlineStart}: 2px`,
`${inlineEnd}: 2px`,
`${inline}: 2px 4px`,
`${blockStart}: 2px`,
`${inlineStart}: var(--x)`,
`${inlineStart}: 2px; ${blockStart}: 3px`,
]) {
prefix_test(
`
.foo {
${decls};
${shorthand}: 0;
}
`,
indoc`
.foo {
${shorthand}: 0;
}
`,
targets,
);
}
});
}

// Safari 14 does not support container query units, so it rejects the whole shorthand and the
// earlier declaration still applies there: it has to stay as a fallback, whether it is logical
// or a physical side whose own new value (5px) would have been fine. Safari 16 supports them,
// so the earlier declaration is dead.
for (const earlier of [`${inlineStart}: 2px`, `${top}: 10px`]) {
prefix_test(
`
.foo {
${earlier};
${shorthand}: 5px max(2cqw, 22px);
}
`,
indoc`
.foo {
${earlier};
${shorthand}: 5px max(2cqw, 22px);
}
`,
{
safari: 14 << 16,
},
);

prefix_test(
`
.foo {
${earlier};
${shorthand}: 5px max(2cqw, 22px);
}
`,
indoc`
.foo {
${shorthand}: 5px max(2cqw, 22px);
}
`,
{
safari: 16 << 16,
},
);
}

// A logical longhand after the shorthand is live and stays.
prefix_test(
`
.foo {
${shorthand}: 0;
${inlineStart}: 2px;
}
`,
indoc`
.foo {
${shorthand}: 0;
${inlineStart}: 2px;
}
`,
{
safari: 15 << 16,
},
);
}

for (const [shorthand, inlineStart, inline, top, left] of [
["margin", "margin-inline-start", "margin-inline", "margin-top", "margin-left"],
["padding", "padding-inline-start", "padding-inline", "padding-top", "padding-left"],
["inset", "inset-inline-start", "inset-inline", "top", "left"],
[
"scroll-margin",
"scroll-margin-inline-start",
"scroll-margin-inline",
"scroll-margin-top",
"scroll-margin-left",
],
]) {
minify_test(`.a{${inlineStart}:2px;${shorthand}:0}`, `.a{${shorthand}:0}`);
minify_test(`.a{${inline}:2px 4px;${shorthand}:0}`, `.a{${shorthand}:0}`);
minify_test(`.a{${inlineStart}:2px!important;${shorthand}:0!important}`, `.a{${shorthand}:0!important}`);
// Longhands after the shorthand still fold into it.
minify_test(`.a{${inlineStart}:2px;${shorthand}:0;${top}:5px}`, `.a{${shorthand}:5px 0 0}`);

// Only the 4-side shorthand overrides the other category: a 2-side logical shorthand leaves
// the physical sides alone (they map to different sides depending on the writing mode), and a
// logical longhand after the shorthand is live.
minify_test(`.a{${left}:2px;${inline}:0}`, `.a{${left}:2px;${inline}:0}`);
minify_test(`.a{${shorthand}:0;${inlineStart}:2px}`, `.a{${shorthand}:0;${inlineStart}:2px}`);
// An unparsed shorthand may hold a value some browser rejects, so the earlier declaration is
// kept as a fallback.
minify_test(`.a{${inlineStart}:2px;${shorthand}:var(--v)}`, `.a{${inlineStart}:2px;${shorthand}:var(--v)}`);
}
});

describe("scroll-paddding", () => {
prefix_test(
`
Expand Down
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