Update specificity calculation for selector pseudos (#1781)

This is very close to invisible to the user and actually making it
visible would require a complex and hard-to-read test, so I'm electing
to avoid testing it.

Closes #2528

CHANGELOG.md

@@ -6,6 +6,8 @@
 * Properly consider `b > c` to be a superselector of `a > b > c`, and similarly
   for other combinators.
 
+* Properly calculate specificity for selector pseudoclasses.
+
 * Deprecate use of `random()` when `$limit` has units to make it explicit that
    `random()` currently ignores units. A future version will no longer ignore
   units.

lib/src/ast/selector/complex.dart

@@ -45,27 +45,13 @@ class ComplexSelector extends Selector {
   @internal
   final bool lineBreak;
 
-  /// The minimum possible specificity that this selector can have.
+  /// This selector's specificity.
   ///
-  /// Pseudo selectors that contain selectors, like `:not()` and `:matches()`,
-  /// can have a range of possible specificities.
-  int get minSpecificity {
-    if (_minSpecificity == null) _computeSpecificity();
-    return _minSpecificity!;
-  }
-
-  int? _minSpecificity;
-
-  /// The maximum possible specificity that this selector can have.
-  ///
-  /// Pseudo selectors that contain selectors, like `:not()` and `:matches()`,
-  /// can have a range of possible specificities.
-  int get maxSpecificity {
-    if (_maxSpecificity == null) _computeSpecificity();
-    return _maxSpecificity!;
-  }
-
-  int? _maxSpecificity;
+  /// Specificity is represented in base 1000. The spec says this should be
+  /// "sufficiently high"; it's extremely unlikely that any single selector
+  /// sequence will contain 1000 simple selectors.
+  late final int specificity = components.fold(
+      0, (sum, component) => sum + component.selector.specificity);
 
   /// If this compound selector is composed of a single compound selector with
   /// no combinators, returns it.
@@ -115,18 +101,6 @@ class ComplexSelector extends Selector {
       other.leadingCombinators.isEmpty &&
       complexIsSuperselector(components, other.components);
 
-  /// Computes [_minSpecificity] and [_maxSpecificity].
-  void _computeSpecificity() {
-    var minSpecificity = 0;
-    var maxSpecificity = 0;
-    for (var component in components) {
-      minSpecificity += component.selector.minSpecificity;
-      maxSpecificity += component.selector.maxSpecificity;
-    }
-    _minSpecificity = minSpecificity;
-    _maxSpecificity = maxSpecificity;
-  }
-
   /// Returns a copy of `this` with [combinators] added to the end of the final
   /// component in [components].
   ///

lib/src/ast/selector/compound.dart

@@ -25,27 +25,13 @@ class CompoundSelector extends Selector {
   /// This is never empty.
   final List<SimpleSelector> components;
 
-  /// The minimum possible specificity that this selector can have.
+  /// This selector's specificity.
   ///
-  /// Pseudo selectors that contain selectors, like `:not()` and `:matches()`,
-  /// can have a range of possible specificities.
-  int get minSpecificity {
-    if (_minSpecificity == null) _computeSpecificity();
-    return _minSpecificity!;
-  }
-
-  int? _minSpecificity;
-
-  /// The maximum possible specificity that this selector can have.
-  ///
-  /// Pseudo selectors that contain selectors, like `:not()` and `:matches()`,
-  /// can have a range of possible specificities.
-  int get maxSpecificity {
-    if (_maxSpecificity == null) _computeSpecificity();
-    return _maxSpecificity!;
-  }
-
-  int? _maxSpecificity;
+  /// Specificity is represented in base 1000. The spec says this should be
+  /// "sufficiently high"; it's extremely unlikely that any single selector
+  /// sequence will contain 1000 simple selectors.
+  late final int specificity =
+      components.fold(0, (sum, component) => sum + component.specificity);
 
   /// If this compound selector is composed of a single simple selector, returns
   /// it.
@@ -87,18 +73,6 @@ class CompoundSelector extends Selector {
   bool isSuperselector(CompoundSelector other) =>
       compoundIsSuperselector(this, other);
 
-  /// Computes [_minSpecificity] and [_maxSpecificity].
-  void _computeSpecificity() {
-    var minSpecificity = 0;
-    var maxSpecificity = 0;
-    for (var simple in components) {
-      minSpecificity += simple.minSpecificity;
-      maxSpecificity += simple.maxSpecificity;
-    }
-    _minSpecificity = minSpecificity;
-    _maxSpecificity = maxSpecificity;
-  }
-
   int get hashCode => listHash(components);
 
   bool operator ==(Object other) =>

lib/src/ast/selector/id.dart

@@ -19,7 +19,7 @@ class IDSelector extends SimpleSelector {
   /// The ID name this selects for.
   final String name;
 
-  int get minSpecificity => math.pow(super.minSpecificity, 2) as int;
+  int get specificity => math.pow(super.specificity, 2) as int;
 
   IDSelector(this.name);
 

lib/src/ast/selector/pseudo.dart

@@ -2,9 +2,8 @@
 // MIT-style license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-import 'dart:math' as math;
-
 import 'package:charcode/charcode.dart';
+import 'package:collection/collection.dart';
 import 'package:meta/meta.dart';
 
 import '../../utils.dart';
@@ -80,19 +79,30 @@ class PseudoSelector extends SimpleSelector {
   /// both non-`null`, the selector follows the argument.
   final SelectorList? selector;
 
-  int get minSpecificity {
-    if (_minSpecificity == null) _computeSpecificity();
-    return _minSpecificity!;
-  }
+  late final int specificity = () {
+    if (isElement) return 1;
+    var selector = this.selector;
+    if (selector == null) return super.specificity;
 
-  int? _minSpecificity;
-
-  int get maxSpecificity {
-    if (_maxSpecificity == null) _computeSpecificity();
-    return _maxSpecificity!;
-  }
-
-  int? _maxSpecificity;
+    // https://drafts.csswg.org/selectors/#specificity-rules
+    switch (normalizedName) {
+      case 'where':
+        return 0;
+      case 'is':
+      case 'not':
+      case 'has':
+      case 'matches':
+        return selector.components
+            .map((component) => component.specificity)
+            .max;
+      case 'nth-child':
+      case 'nth-last-child':
+        return super.specificity +
+            selector.components.map((component) => component.specificity).max;
+      default:
+        return super.specificity;
+    }
+  }();
 
   PseudoSelector(this.name,
       {bool element = false, this.argument, this.selector})
@@ -193,43 +203,6 @@ class PseudoSelector extends SimpleSelector {
     return CompoundSelector([this]).isSuperselector(CompoundSelector([other]));
   }
 
-  /// Computes [_minSpecificity] and [_maxSpecificity].
-  void _computeSpecificity() {
-    if (isElement) {
-      _minSpecificity = 1;
-      _maxSpecificity = 1;
-      return;
-    }
-
-    var selector = this.selector;
-    if (selector == null) {
-      _minSpecificity = super.minSpecificity;
-      _maxSpecificity = super.maxSpecificity;
-      return;
-    }
-
-    if (name == 'not') {
-      var minSpecificity = 0;
-      var maxSpecificity = 0;
-      for (var complex in selector.components) {
-        minSpecificity = math.max(minSpecificity, complex.minSpecificity);
-        maxSpecificity = math.max(maxSpecificity, complex.maxSpecificity);
-      }
-      _minSpecificity = minSpecificity;
-      _maxSpecificity = maxSpecificity;
-    } else {
-      // This is higher than any selector's specificity can actually be.
-      var minSpecificity = math.pow(super.minSpecificity, 3) as int;
-      var maxSpecificity = 0;
-      for (var complex in selector.components) {
-        minSpecificity = math.min(minSpecificity, complex.minSpecificity);
-        maxSpecificity = math.max(maxSpecificity, complex.maxSpecificity);
-      }
-      _minSpecificity = minSpecificity;
-      _maxSpecificity = maxSpecificity;
-    }
-  }
-
   T accept<T>(SelectorVisitor<T> visitor) => visitor.visitPseudoSelector(this);
 
   // This intentionally uses identity for the selector list, if one is available.

lib/src/ast/selector/simple.dart

@@ -27,21 +27,12 @@ final _subselectorPseudos = {
 /// {@category AST}
 /// {@category Parsing}
 abstract class SimpleSelector extends Selector {
-  /// The minimum possible specificity that this selector can have.
-  ///
-  /// Pseudo selectors that contain selectors, like `:not()` and `:matches()`,
-  /// can have a range of possible specificities.
+  /// This selector's specificity.
   ///
   /// Specificity is represented in base 1000. The spec says this should be
   /// "sufficiently high"; it's extremely unlikely that any single selector
   /// sequence will contain 1000 simple selectors.
-  int get minSpecificity => 1000;
-
-  /// The maximum possible specificity that this selector can have.
-  ///
-  /// Pseudo selectors that contain selectors, like `:not()` and `:matches()`,
-  /// can have a range of possible specificities.
-  int get maxSpecificity => minSpecificity;
+  int get specificity => 1000;
 
   SimpleSelector();
 

lib/src/ast/selector/type.dart

@@ -18,7 +18,7 @@ class TypeSelector extends SimpleSelector {
   /// The element name being selected.
   final QualifiedName name;
 
-  int get minSpecificity => 1;
+  int get specificity => 1;
 
   TypeSelector(this.name);
 

lib/src/ast/selector/universal.dart

@@ -21,7 +21,7 @@ class UniversalSelector extends SimpleSelector {
   /// Otherwise, it matches all elements in the given namespace.
   final String? namespace;
 
-  int get minSpecificity => 0;
+  int get specificity => 0;
 
   UniversalSelector({this.namespace});
 

lib/src/extend/extender.dart

@@ -32,10 +32,10 @@ class Extender {
 
   /// Creates a new extender.
   ///
-  /// If [specificity] isn't passed, it defaults to `extender.maxSpecificity`.
+  /// If [specificity] isn't passed, it defaults to `extender.specificity`.
   Extender(this.selector, this.span,
       {this.mediaContext, int? specificity, bool original = false})
-      : specificity = specificity ?? selector.maxSpecificity,
+      : specificity = specificity ?? selector.specificity,
         isOriginal = original;
 
   /// Asserts that the [mediaContext] for a selector is compatible with the

lib/src/extend/extension.dart

@@ -34,8 +34,6 @@ class Extension {
   final FileSpan span;
 
   /// Creates a new extension.
-  ///
-  /// If [specificity] isn't passed, it defaults to `extender.maxSpecificity`.
   Extension(
       ComplexSelector extender, FileSpan extenderSpan, this.target, this.span,
       {this.mediaContext, bool optional = false})
@@ -77,9 +75,9 @@ class Extender {
 
   /// Creates a new extender.
   ///
-  /// If [specificity] isn't passed, it defaults to `extender.maxSpecificity`.
+  /// If [specificity] isn't passed, it defaults to `extender.specificity`.
   Extender(this.selector, this.span, {int? specificity, bool original = false})
-      : specificity = specificity ?? selector.maxSpecificity,
+      : specificity = specificity ?? selector.specificity,
         isOriginal = original;
 
   /// Asserts that the [mediaContext] for a selector is compatible with the

lib/src/extend/extension_store.dart

@@ -261,7 +261,7 @@ class ExtensionStore {
         _extensionsByExtender.putIfAbsent(simple, () => []).add(extension);
         // Only source specificity for the original selector is relevant.
         // Selectors generated by `@extend` don't get new specificity.
-        _sourceSpecificity.putIfAbsent(simple, () => complex.maxSpecificity);
+        _sourceSpecificity.putIfAbsent(simple, () => complex.specificity);
       }
 
       if (selectors != null || existingExtensions != null) {
@@ -970,13 +970,13 @@ class ExtensionStore {
       // trimmed, and thus that if there are two identical selectors only one is
       // trimmed.
       if (result.any((complex2) =>
-          complex2.minSpecificity >= maxSpecificity &&
+          complex2.specificity >= maxSpecificity &&
           complex2.isSuperselector(complex1))) {
         continue;
       }
 
       if (selectors.take(i).any((complex2) =>
-          complex2.minSpecificity >= maxSpecificity &&
+          complex2.specificity >= maxSpecificity &&
           complex2.isSuperselector(complex1))) {
         continue;
       }

lib/src/extend/functions.dart

@@ -657,10 +657,8 @@ bool complexIsSuperselector(List<ComplexSelectorComponent> complex1,
       if (combinator1 == Combinator.followingSibling) {
         // The selector `.foo ~ .bar` is only a superselector of selectors that
         // *exclusively* contain subcombinators of `~`.
-        if (!complex2
-            .take(complex2.length - 1)
-            .skip(i2)
-            .every((component) => _isSupercombinator(
+        if (!complex2.take(complex2.length - 1).skip(i2).every((component) =>
+            _isSupercombinator(
                 combinator1, component.combinators.firstOrNull))) {
           return false;
         }

pkg/sass_api/CHANGELOG.md

@@ -1,6 +1,7 @@
-## 2.0.5
+## 3.0.0
 
-* No user-visible changes.
+* Replace the `minSpecificity` and `maxSpecificity` fields on `ComplexSelector`,
+  `CompoundSelector`, and `SimpleSelector` with a single `specificity` field.
 
 ## 2.0.4
 

pkg/sass_api/pubspec.yaml

@@ -2,7 +2,7 @@ name: sass_api
 # Note: Every time we add a new Sass AST node, we need to bump the *major*
 # version because it's a breaking change for anyone who's implementing the
 # visitor interface(s).
-version: 2.0.5
+version: 3.0.0
 description: Additional APIs for Dart Sass.
 homepage: https://github.com/sass/dart-sass
 

pubspec.yaml

@@ -15,7 +15,7 @@ dependencies:
   async: ^2.5.0
   charcode: ^1.2.0
   cli_repl: ^0.2.1
-  collection: ^1.15.0
+  collection: ^1.16.0
   meta: ^1.3.0
   node_interop: ^2.1.0
   js: ^0.6.3