[css-nesting] Implement CSSNestedDeclarations behind a flag

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. Change-Id: If9afe0cbb41e7de0acdd781ecfbf6884d677c6f8 Binary-Size: crbug.com/344608183 Bug: 343463516 [1] w3c/csswg-drafts#10234
web-platform-tests · Aug 22, 2024 · 1ecb7e8 · 1ecb7e8
1 parent ced507e
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diff --git a/css/css-cascade/scope-nesting.html b/css/css-cascade/scope-nesting.html
@@ -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">

diff --git a/css/css-nesting/nested-declarations-cssom.html b/css/css-nesting/nested-declarations-cssom.html
@@ -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>
diff --git a/css/css-nesting/nested-declarations-matching.html b/css/css-nesting/nested-declarations-matching.html
@@ -0,0 +1,163 @@
+<!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>
diff --git a/css/css-nesting/nesting-basic.html b/css/css-nesting/nesting-basic.html
@@ -68,9 +68,9 @@
 
   .test-10 {
     & {
-      background-color: green;
+      background-color: red;
     }
-    background-color: red;
+    background-color: green;
   }
 
   .test-11 {

diff --git a/css/css-nesting/serialize-group-rules-with-decls.html b/css/css-nesting/serialize-group-rules-with-decls.html
@@ -35,12 +35,12 @@
 
   assert_becomes(
     "div { @media screen { color: red; background-color: green; } }",
-    "div {\n  @media screen {\n  & { color: red; background-color: green; }\n}\n}",
+    "div {\n  @media screen {\n  color: red; background-color: green;\n}\n}",
     "Mixed declarations/rules are on two lines."
   );
   assert_becomes(
     "div {\n  @supports selector(&) { color: red; background-color: green; } &:hover { color: navy; } }",
-    "div {\n  @supports selector(&) {\n  & { color: red; background-color: green; }\n}\n  &:hover { color: navy; }\n}",
+    "div {\n  @supports selector(&) {\n  color: red; background-color: green;\n}\n  &:hover { color: navy; }\n}",
     "Implicit rule is serialized",
   );
 
@@ -62,12 +62,12 @@
   );
   assert_becomes(
     "div { @media screen { color: red; & { color: red; }",
-    "div {\n  @media screen {\n  & { color: red; }\n  & { color: red; }\n}\n}",
+    "div {\n  @media screen {\n  color: red;\n  & { color: red; }\n}\n}",
     "Implicit like rule after decls"
   );
   assert_becomes(
     "div { @media screen { color: red; & { color: blue; }",
-    "div {\n  @media screen {\n  & { color: red; }\n  & { color: blue; }\n}\n}",
+    "div {\n  @media screen {\n  color: red;\n  & { color: blue; }\n}\n}",
     "Implicit like rule after decls, missing closing braces"
   );
   assert_becomes(

diff --git a/css/css-syntax/custom-property-rule-ambiguity.html b/css/css-syntax/custom-property-rule-ambiguity.html
@@ -46,11 +46,12 @@
     assert_equals(rules.length, 1);
     assert_equals(rules[0].selectorText, 'div');
     let div = rules[0];
-    let x = div.style.getPropertyValue('--x');
-    assert_equals(x.trim(), 'hover { }\n    .b { }');
     let childRules = div.cssRules;
-    assert_equals(childRules.length, 1);
+    assert_equals(childRules.length, 2);
     assert_equals(childRules[0].selectorText, '& .a');
+    assert_true(childRules[1] instanceof CSSNestedDeclarations)
+    let x = childRules[1].style.getPropertyValue('--x');
+    assert_equals(x.trim(), 'hover { }\n    .b { }');
   }, 'Nested rule that looks like a custom property declaration');
 </script>