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[css-nesting] Implement CSSNestedDeclarations behind a flag
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The CSSWG recently resolved to change how "bare" declarations work
when mixed with nested style rules. Previously, any declaration
following a nested style rule would be "shifted up" to join
the leading declarations, but as of the work leading up to
Issue 10234 [1], such declarations now instead remain in place
(wrapped in a CSSNestedDeclarations rule).

This CL implements this rule, as well as the parser changes needed
to produce those rules during ConsumeDeclarationList.
The parsing behavior is similar to the behavior previously seen
for emitting signalling/invisible rules (removed in CL:5593832),
although naturally without any signalling, nor any invisibility.

Per spec, CSSNestedDeclarations is a kind of style rule that matches
exactly what its parent style rule matches, and with the same
specificity behavior. This is different from the '&' pseudo-class,
which uses the maximum specificity across its arguments, and can't
match pseudo-elements. This CL implements this via an inner
StyleRule, held by the CSSNestedDeclarations rule.
This inner StyleRule can't be observed via CSSOM. It exists primarily
to be able to bucket the rule normally on RuleSet.

[1] w3c/csswg-drafts#10234

Change-Id: If9afe0cbb41e7de0acdd781ecfbf6884d677c6f8
Binary-Size: crbug.com/344608183
Bug: 343463516, 361600667
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5594117
Reviewed-by: Steinar H Gunderson <sesse@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Philip Pfaffe <pfaffe@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1347266}
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andruud authored and chromium-wpt-export-bot committed Aug 27, 2024
1 parent 957bc89 commit f4e1788
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Showing 6 changed files with 363 additions and 16 deletions.
13 changes: 6 additions & 7 deletions css/css-cascade/scope-nesting.html
Original file line number Diff line number Diff line change
Expand Up @@ -339,16 +339,15 @@
<div>
<style>
.a {
/* We're supposed to prepend :scope to this declaration. If we do that,
then :where() does not matter, since :scope does not gain any
specificity from the enclosing @scope rule. However, if an
implementation incorrectly prepends & instead, then :where() is
needed to avoid the test incorrectly passing due to specificity. */
@scope (:where(&) .b) {
/* The '& .b' selector is wrapped in :where() to prevent a false
positive when the implementation incorrectly wraps
the z-index declaration in a rule with &-behavior
rather than :where(:scope)-behavior. */
@scope (:where(& .b)) {
z-index: 1; /* Should win due to proximity */
}
}
.b { z-index: 2; }
:where(.b) { z-index: 2; }
</style>
<div class=a>
<div class="b x">
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150 changes: 150 additions & 0 deletions css/css-nesting/nested-declarations-cssom.html
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@@ -0,0 +1,150 @@
<!DOCTYPE html>
<title>CSS Nesting: CSSNestedDeclarations CSSOM</title>
<link rel="help" href="https://drafts.csswg.org/css-nesting-1/#nested-declarations-rule">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
test(() => {
let s = new CSSStyleSheet();
s.replaceSync(`
.a {
& { --x:1; }
--x:2;
}
`);
assert_equals(s.cssRules.length, 1);
let outer = s.cssRules[0];
assert_equals(outer.cssRules.length, 2);
assert_equals(outer.cssRules[0].cssText, `& { --x: 1; }`);
assert_equals(outer.cssRules[1].cssText, `--x: 2;`);
}, 'Trailing declarations');

test(() => {
let s = new CSSStyleSheet();
s.replaceSync(`
.a {
--a:1;
--b:1;
& { --c:1; }
--d:1;
--e:1;
& { --f:1; }
--g:1;
--h:1;
--i:1;
& { --j:1; }
--k:1;
--l:1;
}
`);
assert_equals(s.cssRules.length, 1);
let outer = s.cssRules[0];
assert_equals(outer.cssRules.length, 6);
assert_equals(outer.cssRules[0].cssText, `& { --c: 1; }`);
assert_equals(outer.cssRules[1].cssText, `--d: 1; --e: 1;`);
assert_equals(outer.cssRules[2].cssText, `& { --f: 1; }`);
assert_equals(outer.cssRules[3].cssText, `--g: 1; --h: 1; --i: 1;`);
assert_equals(outer.cssRules[4].cssText, `& { --j: 1; }`);
assert_equals(outer.cssRules[5].cssText, `--k: 1; --l: 1;`);
}, 'Mixed declarations');

test(() => {
let s = new CSSStyleSheet();
s.replaceSync(`
.a {
& { --x:1; }
--y:2;
--z:3;
}
`);
assert_equals(s.cssRules.length, 1);
let outer = s.cssRules[0];
assert_equals(outer.cssRules.length, 2);
let nested_declarations = outer.cssRules[1];
assert_true(nested_declarations instanceof CSSNestedDeclarations);
assert_equals(nested_declarations.style.length, 2);
assert_equals(nested_declarations.style.getPropertyValue('--x'), '');
assert_equals(nested_declarations.style.getPropertyValue('--y'), '2');
assert_equals(nested_declarations.style.getPropertyValue('--z'), '3');
}, 'CSSNestedDeclarations.style');

test(() => {
let s = new CSSStyleSheet();
s.replaceSync(`
.a {
@media (width > 100px) {
--x:1;
--y:1;
.b { }
--z:1;
}
--w:1;
}
`);
assert_equals(s.cssRules.length, 1);
let outer = s.cssRules[0];
assert_equals(outer.cssRules.length, 2);

// @media
let media = outer.cssRules[0];
assert_equals(media.cssRules.length, 3);
assert_true(media.cssRules[0] instanceof CSSNestedDeclarations);
assert_equals(media.cssRules[0].cssText, `--x: 1; --y: 1;`);
assert_equals(media.cssRules[1].cssText, `& .b { }`);
assert_true(media.cssRules[2] instanceof CSSNestedDeclarations);
assert_equals(media.cssRules[2].cssText, `--z: 1;`);

assert_true(outer.cssRules[1] instanceof CSSNestedDeclarations);
assert_equals(outer.cssRules[1].cssText, `--w: 1;`);
}, 'Nested group rule');

test(() => {
let s = new CSSStyleSheet();
s.replaceSync(`
.a {
@scope (.foo) {
--x:1;
--y:1;
.b { }
--z:1;
}
--w:1;
}
`);
assert_equals(s.cssRules.length, 1);
let outer = s.cssRules[0];
assert_equals(outer.cssRules.length, 2);

// @scope
let scope = outer.cssRules[0];
assert_equals(scope.cssRules.length, 3);
assert_true(scope.cssRules[0] instanceof CSSNestedDeclarations);
assert_equals(scope.cssRules[0].cssText, `--x: 1; --y: 1;`);
assert_equals(scope.cssRules[1].cssText, `.b { }`); // Implicit :scope here.
assert_true(scope.cssRules[2] instanceof CSSNestedDeclarations);
assert_equals(scope.cssRules[2].cssText, `--z: 1;`);

assert_true(outer.cssRules[1] instanceof CSSNestedDeclarations);
assert_equals(outer.cssRules[1].cssText, `--w: 1;`);
}, 'Nested @scope rule');

test(() => {
let s = new CSSStyleSheet();
s.replaceSync(`
a {
& { --x:1; }
width: 100px;
height: 200px;
color:hover {}
--y: 2;
}
`);
assert_equals(s.cssRules.length, 1);
let outer = s.cssRules[0];
assert_equals(outer.cssRules.length, 4);
assert_equals(outer.cssRules[0].cssText, `& { --x: 1; }`);
assert_equals(outer.cssRules[1].cssText, `width: 100px; height: 200px;`);
assert_equals(outer.cssRules[2].cssText, `& color:hover { }`);
assert_equals(outer.cssRules[3].cssText, `--y: 2;`);
}, 'Inner rule starting with an ident');
</script>
197 changes: 197 additions & 0 deletions css/css-nesting/nested-declarations-matching.html
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@@ -0,0 +1,197 @@
<!DOCTYPE html>
<title>CSS Nesting: CSSNestedDeclarations matching</title>
<link rel="help" href="https://drafts.csswg.org/css-nesting-1/#nested-declarations-rule">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<style>
.trailing {
--x: FAIL;
& { --x: FAIL; }
--x: PASS;
}
</style>
<div class=trailing></div>
<script>
test(() => {
let e = document.querySelector('.trailing');
assert_equals(getComputedStyle(e).getPropertyValue('--x'), 'PASS');
}, 'Trailing declarations apply after any preceding rules');
</script>


<style>
.trailing_no_leading {
& { --x: FAIL; }
--x: PASS;
}
</style>
<div class=trailing_no_leading></div>
<script>
test(() => {
let e = document.querySelector('.trailing_no_leading');
assert_equals(getComputedStyle(e).getPropertyValue('--x'), 'PASS');
}, 'Trailing declarations apply after any preceding rules (no leading)');
</script>


<style>
.trailing_multiple {
--x: FAIL;
--y: FAIL;
--z: FAIL;
--w: FAIL;
& { --x: FAIL; }
--x: PASS;
--y: PASS;
& { --z: FAIL; }
--z: PASS;
--w: PASS;
}
</style>
<div class=trailing_multiple></div>
<script>
test(() => {
let e = document.querySelector('.trailing_multiple');
let s = getComputedStyle(e);
assert_equals(s.getPropertyValue('--x'), 'PASS');
assert_equals(s.getPropertyValue('--y'), 'PASS');
assert_equals(s.getPropertyValue('--z'), 'PASS');
assert_equals(s.getPropertyValue('--w'), 'PASS');
}, 'Trailing declarations apply after any preceding rules (multiple)');
</script>


<style>
.trailing_specificity {
--x: FAIL;
:is(&, div.nomatch2) { --x: PASS; } /* Specificity: (0, 1, 1) */
--x: FAIL; /* Specificity: (0, 1, 0) */
}
</style>
<div class=trailing_specificity></div>
<script>
test(() => {
let e = document.querySelector('.trailing_specificity');
assert_equals(getComputedStyle(e).getPropertyValue('--x'), 'PASS');
}, 'Nested declarations rule has same specificity as outer selector');
</script>


<style>
#nomatch, .specificity_top_level {
--x: FAIL;
:is(&, div.nomatch2) { --x: PASS; } /* Specificity: (0, 1, 1) */
--x: FAIL; /* Specificity: (0, 1, 0). In particular, this does not have
specificity like :is(#nomatch, .specificity_top_level). */
}
</style>
<div class=specificity_top_level></div>
<script>
test(() => {
let e = document.querySelector('.specificity_top_level');
assert_equals(getComputedStyle(e).getPropertyValue('--x'), 'PASS');
}, 'Nested declarations rule has top-level specificity behavior');
</script>


<style>
#nomatch, .specificity_top_level_max, div.specificity_top_level_max {
--x: FAIL;
:is(:where(&), div.nomatch2) { --x: FAIL; } /* Specificity: (0, 1, 1) */
--x: PASS; /* Specificity: (0, 1, 1) (for div.specificity_top_level_max) */
}
</style>
<div class=specificity_top_level_max></div>
<script>
test(() => {
let e = document.querySelector('.specificity_top_level_max');
assert_equals(getComputedStyle(e).getPropertyValue('--x'), 'PASS');
}, 'Nested declarations rule has top-level specificity behavior (max matching)');
</script>

<style>
.nested_pseudo::after {
--x: FAIL;
@media (width > 0px) {
--x: PASS;
}
}
</style>
<div class=nested_pseudo></div>
<script>
test(() => {
let e = document.querySelector('.nested_pseudo');
assert_equals(getComputedStyle(e, '::after').getPropertyValue('--x'), 'PASS');
}, 'Bare declartaion in nested grouping rule can match pseudo-element');
</script>

<style>
#nomatch, .nested_group_rule {
--x: FAIL;
@media (width > 0px) {
--x: FAIL; /* Specificity: (0, 1, 0) */
}
--x: PASS;
}
</style>
<div class=nested_group_rule></div>
<script>
test(() => {
let e = document.querySelector('.nested_group_rule');
assert_equals(getComputedStyle(e).getPropertyValue('--x'), 'PASS');
}, 'Nested group rules have top-level specificity behavior');
</script>


<style>
.nested_scope_rule {
div:where(&) { /* Specificity: (0, 0, 1) */
--x: PASS;
}
@scope (&) {
--x: FAIL; /* Specificity: (0, 0, 0) */
}
}
</style>
<div class=nested_scope_rule></div>
<script>
test(() => {
let e = document.querySelector('.nested_scope_rule');
assert_equals(getComputedStyle(e).getPropertyValue('--x'), 'PASS');
}, 'Nested @scope rules behave like :where(:scope)');
</script>

<style id=set_parent_selector_text_style>
.set_parent_selector_text {
div {
color: red;
}
.a1 {
& { color: green };
}
}
</style>
<div class=set_parent_selector_text>
<div class=a1>A1</div>
<div class=a2>A2</div>
</div>
<script>
test(() => {
let a1 = document.querySelector('.set_parent_selector_text > .a1');
let a2 = document.querySelector('.set_parent_selector_text > .a2');
assert_equals(getComputedStyle(a1).color, 'rgb(0, 128, 0)');
assert_equals(getComputedStyle(a2).color, 'rgb(255, 0, 0)');

let rules = set_parent_selector_text_style.sheet.cssRules;
assert_equals(rules.length, 1);
assert_equals(rules[0].cssRules.length, 2);

let a_rule = rules[0].cssRules[1];
assert_equals(a_rule.selectorText, '& .a1');
a_rule.selectorText = '.a2';

assert_equals(getComputedStyle(a1).color, 'rgb(255, 0, 0)');
assert_equals(getComputedStyle(a2).color, 'rgb(0, 128, 0)');
}, 'Nested declarations rule responds to parent selector text change');
</script>
4 changes: 2 additions & 2 deletions css/css-nesting/nesting-basic.html
Original file line number Diff line number Diff line change
Expand Up @@ -68,9 +68,9 @@

.test-10 {
& {
background-color: green;
background-color: red;
}
background-color: red;
background-color: green;
}

.test-11 {
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