Fix superselector bugs for pseudo-elements and universal selectors (#1753)

Closes #790
Closes sass/sass#2728

Author: nex3

CHANGELOG.md

@@ -18,6 +18,11 @@
 
 * Deprecate passing non-`deg` units to `color.hwb()`'s `$hue` argument.
 
+* Fix a number of bugs when determining whether selectors with pseudo-elements
+  are superselectors.
+
+* Treat `*` as a superselector of all selectors.
+
 ### Dart API
 
 * Add a top-level `fakeFromImport()` function for testing custom importers

lib/src/ast/selector/pseudo.dart

@@ -8,6 +8,7 @@ import 'package:charcode/charcode.dart';
 import 'package:meta/meta.dart';
 
 import '../../utils.dart';
+import '../../util/nullable.dart';
 import '../../visitor/interface/selector.dart';
 import '../selector.dart';
 
@@ -174,6 +175,24 @@ class PseudoSelector extends SimpleSelector {
     return result;
   }
 
+  bool isSuperselector(SimpleSelector other) {
+    if (super.isSuperselector(other)) return true;
+
+    var selector = this.selector;
+    if (selector == null) return this == other;
+    if (other is PseudoSelector &&
+        isElement &&
+        other.isElement &&
+        normalizedName == 'slotted' &&
+        other.name == name) {
+      return other.selector.andThen(selector.isSuperselector) ?? false;
+    }
+
+    // Fall back to the logic defined in functions.dart, which knows how to
+    // compare selector pseudoclasses against raw selectors.
+    return CompoundSelector([this]).isSuperselector(CompoundSelector([other]));
+  }
+
   /// Computes [_minSpecificity] and [_maxSpecificity].
   void _computeSpecificity() {
     if (isElement) {

lib/src/ast/selector/simple.dart

@@ -9,6 +9,19 @@ import '../../logger.dart';
 import '../../parse/selector.dart';
 import '../selector.dart';
 
+/// Names of pseudo-classes that take selectors as arguments, and that are
+/// subselectors of the union of their arguments.
+///
+/// For example, `.foo` is a superselector of `:matches(.foo)`.
+final _subselectorPseudos = {
+  'is',
+  'matches',
+  'where',
+  'any',
+  'nth-child',
+  'nth-last-child'
+};
+
 /// An abstract superclass for simple selectors.
 ///
 /// {@category AST}
@@ -92,4 +105,22 @@ abstract class SimpleSelector extends Selector {
 
     return result;
   }
+
+  /// Whether this is a superselector of [other].
+  ///
+  /// That is, whether this matches every element that [other] matches, as well
+  /// as possibly additional elements.
+  bool isSuperselector(SimpleSelector other) {
+    if (this == other) return true;
+    if (other is PseudoSelector && other.isClass) {
+      var list = other.selector;
+      if (list != null && _subselectorPseudos.contains(other.normalizedName)) {
+        return list.components.every((complex) =>
+            complex.components.isNotEmpty &&
+            complex.components.last.selector.components
+                .any((simple) => isSuperselector(simple)));
+      }
+    }
+    return false;
+  }
 }

lib/src/ast/selector/type.dart

@@ -41,6 +41,12 @@ class TypeSelector extends SimpleSelector {
     }
   }
 
+  bool isSuperselector(SimpleSelector other) =>
+      super.isSuperselector(other) ||
+      (other is TypeSelector &&
+          name.name == other.name.name &&
+          (name.namespace == '*' || name.namespace == other.name.namespace));
+
   bool operator ==(Object other) => other is TypeSelector && other.name == name;
 
   int get hashCode => name.hashCode;

lib/src/ast/selector/universal.dart

@@ -47,6 +47,13 @@ class UniversalSelector extends SimpleSelector {
     return [this];
   }
 
+  bool isSuperselector(SimpleSelector other) {
+    if (namespace == '*') return true;
+    if (other is TypeSelector) return namespace == other.name.namespace;
+    if (other is UniversalSelector) return namespace == other.namespace;
+    return namespace == null || super.isSuperselector(other);
+  }
+
   bool operator ==(Object other) =>
       other is UniversalSelector && other.namespace == namespace;
 

lib/src/extend/functions.dart

@@ -13,23 +13,11 @@
 import 'dart:collection';
 
 import 'package:collection/collection.dart';
+import 'package:tuple/tuple.dart';
 
 import '../ast/selector.dart';
 import '../utils.dart';
 
-/// Names of pseudo selectors that take selectors as arguments, and that are
-/// subselectors of their arguments.
-///
-/// For example, `.foo` is a superselector of `:matches(.foo)`.
-final _subselectorPseudos = {
-  'is',
-  'matches',
-  'where',
-  'any',
-  'nth-child',
-  'nth-last-child'
-};
-
 /// Returns the contents of a [SelectorList] that matches only elements that are
 /// matched by every complex selector in [complexes].
 ///
@@ -689,6 +677,29 @@ bool complexIsSuperselector(List<ComplexSelectorComponent> complex1,
 bool compoundIsSuperselector(
     CompoundSelector compound1, CompoundSelector compound2,
     {Iterable<ComplexSelectorComponent>? parents}) {
+  // Pseudo elements effectively change the target of a compound selector rather
+  // than narrowing the set of elements to which it applies like other
+  // selectors. As such, if either selector has a pseudo element, they both must
+  // have the _same_ pseudo element.
+  //
+  // In addition, order matters when pseudo-elements are involved. The selectors
+  // before them must
+  var tuple1 = _findPseudoElementIndexed(compound1);
+  var tuple2 = _findPseudoElementIndexed(compound2);
+  if (tuple1 != null && tuple2 != null) {
+    return tuple1.item1.isSuperselector(tuple2.item1) &&
+        _compoundComponentsIsSuperselector(
+            compound1.components.take(tuple1.item2),
+            compound2.components.take(tuple2.item2),
+            parents: parents) &&
+        _compoundComponentsIsSuperselector(
+            compound1.components.skip(tuple1.item2 + 1),
+            compound2.components.skip(tuple2.item2 + 1),
+            parents: parents);
+  } else if (tuple1 != null || tuple2 != null) {
+    return false;
+  }
+
   // Every selector in [compound1.components] must have a matching selector in
   // [compound2.components].
   for (var simple1 in compound1.components) {
@@ -697,49 +708,44 @@ bool compoundIsSuperselector(
           parents: parents)) {
         return false;
       }
-    } else if (!_simpleIsSuperselectorOfCompound(simple1, compound2)) {
-      return false;
-    }
-  }
-
-  // [compound1] can't be a superselector of a selector with non-selector
-  // pseudo-elements that [compound2] doesn't share.
-  for (var simple2 in compound2.components) {
-    if (simple2 is PseudoSelector &&
-        simple2.isElement &&
-        simple2.selector == null &&
-        !_simpleIsSuperselectorOfCompound(simple2, compound1)) {
+    } else if (!compound2.components.any(simple1.isSuperselector)) {
       return false;
     }
   }
 
   return true;
 }
 
-/// Returns whether [simple] is a superselector of [compound].
+/// If [compound] contains a pseudo-element, returns it and its index in
+/// [compound.components].
+Tuple2<PseudoSelector, int>? _findPseudoElementIndexed(
+    CompoundSelector compound) {
+  for (var i = 0; i < compound.components.length; i++) {
+    var simple = compound.components[i];
+    if (simple is PseudoSelector && simple.isElement) return Tuple2(simple, i);
+  }
+  return null;
+}
+
+/// Like [compoundIsSuperselector] but operates on the underlying lists of
+/// simple selectors.
 ///
-/// That is, whether [simple] matches every element that [compound] matches, as
-/// well as possibly additional elements.
-bool _simpleIsSuperselectorOfCompound(
-    SimpleSelector simple, CompoundSelector compound) {
-  return compound.components.any((theirSimple) {
-    if (simple == theirSimple) return true;
-
-    // Some selector pseudoclasses can match normal selectors.
-    if (theirSimple is! PseudoSelector) return false;
-    var selector = theirSimple.selector;
-    if (selector == null) return false;
-    if (!_subselectorPseudos.contains(theirSimple.normalizedName)) return false;
-
-    return selector.components.every((complex) =>
-        complex.singleCompound?.components.contains(simple) ?? false);
-  });
+/// The [compound1] and [compound2] are expected to have efficient
+/// [Iterable.length] fields.
+bool _compoundComponentsIsSuperselector(
+    Iterable<SimpleSelector> compound1, Iterable<SimpleSelector> compound2,
+    {Iterable<ComplexSelectorComponent>? parents}) {
+  if (compound1.isEmpty) return true;
+  if (compound2.isEmpty) compound2 = [UniversalSelector(namespace: '*')];
+  return compoundIsSuperselector(
+      CompoundSelector(compound1), CompoundSelector(compound2),
+      parents: parents);
 }
 
 /// Returns whether [pseudo1] is a superselector of [compound2].
 ///
-/// That is, whether [pseudo1] matches every element that [compound2] matches, as well
-/// as possibly additional elements.
+/// That is, whether [pseudo1] matches every element that [compound2] matches,
+/// as well as possibly additional elements.
 ///
 /// This assumes that [pseudo1]'s `selector` argument is not `null`.
 ///