Deprecated mixed declarations

lib/src/ast/sass.dart

@@ -54,6 +54,7 @@ export 'sass/statement/include_rule.dart';
 export 'sass/statement/loud_comment.dart';
 export 'sass/statement/media_rule.dart';
 export 'sass/statement/mixin_rule.dart';
+export 'sass/statement/nest_rule.dart';
 export 'sass/statement/parent.dart';
 export 'sass/statement/return_rule.dart';
 export 'sass/statement/silent_comment.dart';

lib/src/ast/sass/statement/nest_rule.dart

@@ -0,0 +1,28 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:source_span/source_span.dart';
+
+import '../../../visitor/interface/statement.dart';
+import '../statement.dart';
+import 'parent.dart';
+
+/// A `@nest` rule.
+///
+/// This ensures that the nesting and ordering of its contents match that
+/// [specified by CSS].
+///
+/// [specified by CSS]: https://drafts.csswg.org/css-nesting/#mixing
+///
+/// {@category AST}
+final class NestRule extends ParentStatement<List<Statement>> {
+  final FileSpan span;
+
+  NestRule(Iterable<Statement> children, this.span)
+      : super(List.unmodifiable(children));
+
+  T accept<T>(StatementVisitor<T> visitor) => visitor.visitNestRule(this);
+
+  String toString() => "@nest {${children.join(' ')}}";
+}

lib/src/deprecation.dart

@@ -15,7 +15,7 @@ enum Deprecation {
   // DO NOT EDIT. This section was generated from the language repo.
   // See tool/grind/generate_deprecations.dart for details.
   //
-  // Checksum: 22d9bdbe92eb39b3c0d6d64ebe1879a431c0037e
+  // Checksum: 309e4f1f008f08379b824ab6094e13df2e18e187
 
   /// Deprecation for passing a string directly to meta.call().
   callString('call-string',
@@ -90,6 +90,11 @@ enum Deprecation {
       deprecatedIn: '1.76.0',
       description: 'Function and mixin names beginning with --.'),
 
+  /// Deprecation for declarations after or between nested rules.
+  mixedDecls('mixed-decls',
+      deprecatedIn: '1.77.7',
+      description: 'Declarations after or between nested rules.'),
+
   /// Deprecation for @import rules.
   import.future('import', description: '@import rules.'),
 

lib/src/parse/css.dart

@@ -42,7 +42,7 @@ class CssParser extends ScssParser {
   }
 
   Statement atRule(Statement child(), {bool root = false}) {
-    // NOTE: this logic is largely duplicated in CssParser.atRule. Most changes
+    // NOTE: this logic is largely duplicated in StylesheetParser.atRule. Most changes
     // here should be mirrored there.
 
     var start = scanner.state;
@@ -65,17 +65,18 @@ class CssParser extends ScssParser {
       "return" ||
       "warn" ||
       "while" =>
-        _forbiddenAtRoot(start),
+        _forbiddenAtRule(start),
       "import" => _cssImportRule(start),
       "media" => mediaRule(start),
       "-moz-document" => mozDocumentRule(start, name),
       "supports" => supportsRule(start),
+      var name? when name.toLowerCase() == "nest" => nestRule(start),
       _ => unknownAtRule(start, name)
     };
   }
 
   /// Throws an error for a forbidden at-rule.
-  Never _forbiddenAtRoot(LineScannerState start) {
+  Never _forbiddenAtRule(LineScannerState start) {
     almostAnyValue();
     error("This at-rule isn't allowed in plain CSS.", scanner.spanFrom(start));
   }

lib/src/parse/stylesheet.dart

@@ -649,6 +649,8 @@ abstract class StylesheetParser extends Parser {
         return _warnRule(start);
       case "while":
         return _whileRule(start, child);
+      case var name? when name.toLowerCase() == "nest":
+        return nestRule(start);
       default:
         return unknownAtRule(start, name);
     }
@@ -1400,6 +1402,22 @@ abstract class StylesheetParser extends Parser {
     });
   }
 
+  /// Consumes a `@return` rule.
+  ///
+  /// [start] should point before the `@`.
+  @protected
+  NestRule nestRule(LineScannerState start) {
+    whitespace();
+    var wasInUnknownAtRule = _inUnknownAtRule;
+    _inUnknownAtRule = true;
+    try {
+      return _withChildren(
+          _statement, start, (children, span) => NestRule(children, span));
+    } finally {
+      _inUnknownAtRule = wasInUnknownAtRule;
+    }
+  }
+
   /// Consumes a `@return` rule.
   ///
   /// [start] should point before the `@`.

lib/src/visitor/async_evaluate.dart

@@ -1189,6 +1189,20 @@ final class _EvaluateVisitor
           node.span);
     }
 
+    if (_parent.parent!.children.last case var sibling
+        when _parent != sibling) {
+      _warn(
+          "Sass's behavior for declarations that appear after nested\n"
+          "rules will be changing to match the behavior specified by CSS in an "
+          "upcoming\n"
+          "version. To keep the existing behavior, move the declaration above "
+          "the nested\n"
+          "rule. To opt into the new behavior, wrap the declaration in `@nest "
+          "{}`.",
+          MultiSpan(node.span, 'declaration', {sibling.span: 'nested rule'}),
+          Deprecation.mixedDecls);
+    }
+
     var name = await _interpolationToValue(node.name, warnForColor: true);
     if (_declarationName case var declarationName?) {
       name = CssValue("$declarationName-${name.value}", name.span);
@@ -1884,6 +1898,53 @@ final class _EvaluateVisitor
     return null;
   }
 
+  Future<Value?> visitNestRule(NestRule node) async {
+    if (_declarationName != null) {
+      throw _exception(
+          "At-rules may not be used within nested declarations.", node.span);
+    } else if (_inKeyframes) {
+      throw _exception(
+          "@nest may not be used within a keyframe block.", node.span);
+    }
+
+    var wasInUnknownAtRule = _inUnknownAtRule;
+    var oldAtRootExcludingStyleRule = _atRootExcludingStyleRule;
+    _inUnknownAtRule = true;
+    _atRootExcludingStyleRule = false;
+    if (_styleRule case var styleRule?) {
+      if (_stylesheet.plainCss) {
+        for (var child in node.children) {
+          await child.accept(this);
+        }
+      } else {
+        var newStyleRule = styleRule.copyWithoutChildren();
+        await _withParent(newStyleRule, () async {
+          await _withStyleRule(newStyleRule, () async {
+            for (var child in node.children) {
+              await child.accept(this);
+            }
+          });
+        },
+            through: (node) => node is CssStyleRule,
+            scopeWhen: node.hasDeclarations);
+
+        _warnForBogusCombinators(newStyleRule);
+      }
+    } else {
+      await _withParent(
+          ModifiableCssAtRule(CssValue("nest", node.span), node.span),
+          () async {
+        for (var child in node.children) {
+          await child.accept(this);
+        }
+      }, scopeWhen: node.hasDeclarations);
+    }
+    _inUnknownAtRule = wasInUnknownAtRule;
+    _atRootExcludingStyleRule = oldAtRootExcludingStyleRule;
+
+    return null;
+  }
+
   Future<Value?> visitLoudComment(LoudComment node) async {
     // NOTE: this logic is largely duplicated in [visitCssComment]. Most changes
     // here should be mirrored there.
@@ -2065,8 +2126,20 @@ final class _EvaluateVisitor
         scopeWhen: node.hasDeclarations);
     _atRootExcludingStyleRule = oldAtRootExcludingStyleRule;
 
+    _warnForBogusCombinators(rule);
+
+    if (_styleRule == null && _parent.children.isNotEmpty) {
+      var lastChild = _parent.children.last;
+      lastChild.isGroupEnd = true;
+    }
+
+    return null;
+  }
+
+  /// Emits deprecation warnings for any bogus combinators in [rule].
+  void _warnForBogusCombinators(CssStyleRule rule) {
     if (!rule.isInvisibleOtherThanBogusCombinators) {
-      for (var complex in parsedSelector.components) {
+      for (var complex in rule.selector.components) {
         if (!complex.isBogus) continue;
 
         if (complex.isUseless) {
@@ -2110,13 +2183,6 @@ final class _EvaluateVisitor
         }
       }
     }
-
-    if (_styleRule == null && _parent.children.isNotEmpty) {
-      var lastChild = _parent.children.last;
-      lastChild.isGroupEnd = true;
-    }
-
-    return null;
   }
 
   Future<Value?> visitSupportsRule(SupportsRule node) async {

lib/src/visitor/evaluate.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: 116b8079719577ac6e4dad4aebe403282136e611
+// Checksum: e1e8310eb9afa8042569f8a706341ae983fd78ee
 //
 // ignore_for_file: unused_import
 
@@ -1187,6 +1187,20 @@ final class _EvaluateVisitor
           node.span);
     }
 
+    if (_parent.parent!.children.last case var sibling
+        when _parent != sibling) {
+      _warn(
+          "Sass's behavior for declarations that appear after nested\n"
+          "rules will be changing to match the behavior specified by CSS in an "
+          "upcoming\n"
+          "version. To keep the existing behavior, move the declaration above "
+          "the nested\n"
+          "rule. To opt into the new behavior, wrap the declaration in `@nest "
+          "{}`.",
+          MultiSpan(node.span, 'declaration', {sibling.span: 'nested rule'}),
+          Deprecation.mixedDecls);
+    }
+
     var name = _interpolationToValue(node.name, warnForColor: true);
     if (_declarationName case var declarationName?) {
       name = CssValue("$declarationName-${name.value}", name.span);
@@ -1876,6 +1890,52 @@ final class _EvaluateVisitor
     return null;
   }
 
+  Value? visitNestRule(NestRule node) {
+    if (_declarationName != null) {
+      throw _exception(
+          "At-rules may not be used within nested declarations.", node.span);
+    } else if (_inKeyframes) {
+      throw _exception(
+          "@nest may not be used within a keyframe block.", node.span);
+    }
+
+    var wasInUnknownAtRule = _inUnknownAtRule;
+    var oldAtRootExcludingStyleRule = _atRootExcludingStyleRule;
+    _inUnknownAtRule = true;
+    _atRootExcludingStyleRule = false;
+    if (_styleRule case var styleRule?) {
+      if (_stylesheet.plainCss) {
+        for (var child in node.children) {
+          child.accept(this);
+        }
+      } else {
+        var newStyleRule = styleRule.copyWithoutChildren();
+        _withParent(newStyleRule, () {
+          _withStyleRule(newStyleRule, () {
+            for (var child in node.children) {
+              child.accept(this);
+            }
+          });
+        },
+            through: (node) => node is CssStyleRule,
+            scopeWhen: node.hasDeclarations);
+
+        _warnForBogusCombinators(newStyleRule);
+      }
+    } else {
+      _withParent(ModifiableCssAtRule(CssValue("nest", node.span), node.span),
+          () {
+        for (var child in node.children) {
+          child.accept(this);
+        }
+      }, scopeWhen: node.hasDeclarations);
+    }
+    _inUnknownAtRule = wasInUnknownAtRule;
+    _atRootExcludingStyleRule = oldAtRootExcludingStyleRule;
+
+    return null;
+  }
+
   Value? visitLoudComment(LoudComment node) {
     // NOTE: this logic is largely duplicated in [visitCssComment]. Most changes
     // here should be mirrored there.
@@ -2055,8 +2115,20 @@ final class _EvaluateVisitor
         scopeWhen: node.hasDeclarations);
     _atRootExcludingStyleRule = oldAtRootExcludingStyleRule;
 
+    _warnForBogusCombinators(rule);
+
+    if (_styleRule == null && _parent.children.isNotEmpty) {
+      var lastChild = _parent.children.last;
+      lastChild.isGroupEnd = true;
+    }
+
+    return null;
+  }
+
+  /// Emits deprecation warnings for any bogus combinators in [rule].
+  void _warnForBogusCombinators(CssStyleRule rule) {
     if (!rule.isInvisibleOtherThanBogusCombinators) {
-      for (var complex in parsedSelector.components) {
+      for (var complex in rule.selector.components) {
         if (!complex.isBogus) continue;
 
         if (complex.isUseless) {
@@ -2100,13 +2172,6 @@ final class _EvaluateVisitor
         }
       }
     }
-
-    if (_styleRule == null && _parent.children.isNotEmpty) {
-      var lastChild = _parent.children.last;
-      lastChild.isGroupEnd = true;
-    }
-
-    return null;
   }
 
   Value? visitSupportsRule(SupportsRule node) {

lib/src/visitor/interface/statement.dart

@@ -28,6 +28,7 @@ abstract interface class StatementVisitor<T> {
   T visitLoudComment(LoudComment node);
   T visitMediaRule(MediaRule node);
   T visitMixinRule(MixinRule node);
+  T visitNestRule(NestRule node);
   T visitReturnRule(ReturnRule node);
   T visitSilentComment(SilentComment node);
   T visitStyleRule(StyleRule node);

lib/src/visitor/recursive_statement.dart

@@ -71,6 +71,8 @@ mixin RecursiveStatementVisitor implements StatementVisitor<void> {
 
   void visitMixinRule(MixinRule node) => visitCallableDeclaration(node);
 
+  void visitNestRule(NestRule node) => visitChildren(node.children);
+
   void visitReturnRule(ReturnRule node) {}
 
   void visitSilentComment(SilentComment node) {}

lib/src/visitor/statement_search.dart

@@ -61,6 +61,8 @@ mixin StatementSearchVisitor<T> implements StatementVisitor<T?> {
 
   T? visitMixinRule(MixinRule node) => visitCallableDeclaration(node);
 
+  T? visitNestRule(NestRule node) => visitChildren(node.children);
+
   T? visitReturnRule(ReturnRule node) => null;
 
   T? visitSilentComment(SilentComment node) => null;