Properly parse custom property values in @supports conditions (#1570)

Closes sass/sass#3216

Author: nex3

CHANGELOG.md

@@ -1,5 +1,10 @@
 ## 1.45.1
 
+* **Potentially breaking bug fix:** Properly parse custom properties in
+  `@supports` conditions. Note that this means that SassScript expressions on
+  the right-hand side of custom property `@supports` queries now need to be
+  interpolated, as per https://sass-lang.com/d/css-vars.
+
 * **Potentially breaking bug fix:** Fix a bug where `inspect()` was not
   properly printing nested, empty, bracketed lists.
 

lib/src/ast/sass/supports_condition/declaration.dart

@@ -6,6 +6,7 @@ import 'package:meta/meta.dart';
 import 'package:source_span/source_span.dart';
 
 import '../expression.dart';
+import '../expression/string.dart';
 import '../supports_condition.dart';
 
 /// A condition that selects for browsers where a given declaration is
@@ -22,6 +23,23 @@ class SupportsDeclaration implements SupportsCondition {
 
   final FileSpan span;
 
+  /// Returns whether this is a CSS Custom Property declaration.
+  ///
+  /// Note that this can return `false` for declarations that will ultimately be
+  /// serialized as custom properties if they aren't *parsed as* custom
+  /// properties, such as `#{--foo}: ...`.
+  ///
+  /// If this is `true`, then `value` will be a [StringExpression].
+  ///
+  /// @nodoc
+  @internal
+  bool get isCustomProperty {
+    var name = this.name;
+    return name is StringExpression &&
+        !name.hasQuotes &&
+        name.text.initialPlain.startsWith('--');
+  }
+
   SupportsDeclaration(this.name, this.value, this.span);
 
   String toString() => "($name: $value)";

lib/src/parse/stylesheet.dart

@@ -1172,9 +1172,7 @@ abstract class StylesheetParser extends Parser {
         if (supports == null) {
           var name = expression();
           scanner.expectChar($colon);
-          whitespace();
-          var value = expression();
-          supports = SupportsDeclaration(name, value, scanner.spanFrom(start));
+          supports = _supportsDeclarationValue(name, start);
         }
       }
       scanner.expectChar($rparen);
@@ -3611,9 +3609,24 @@ abstract class StylesheetParser extends Parser {
       return SupportsAnything(contents, scanner.spanFrom(start));
     }
 
-    whitespace();
-    var value = expression();
+    var declaration = _supportsDeclarationValue(name, start);
     scanner.expectChar($rparen);
+    return declaration;
+  }
+
+  /// Parses and returns the right-hand side of a declaration in a supports
+  /// query.
+  SupportsDeclaration _supportsDeclarationValue(
+      Expression name, LineScannerState start) {
+    Expression value;
+    if (name is StringExpression &&
+        !name.hasQuotes &&
+        name.text.initialPlain.startsWith("--")) {
+      value = StringExpression(_interpolatedDeclarationValue());
+    } else {
+      whitespace();
+      value = expression();
+    }
     return SupportsDeclaration(name, value, scanner.spanFrom(start));
   }
 

lib/src/visitor/async_evaluate.dart

@@ -1656,7 +1656,8 @@ class _EvaluateVisitor
     var url = await _interpolationToValue(import.url);
     var supports = await import.supports.andThen((supports) async {
       var arg = supports is SupportsDeclaration
-          ? "${await _evaluateToCss(supports.name)}: "
+          ? "${await _evaluateToCss(supports.name)}:"
+              "${supports.isCustomProperty ? '' : ' '}"
               "${await _evaluateToCss(supports.value)}"
           : await supports.andThen(_visitSupportsCondition);
       return CssValue("supports($arg)", supports.span);
@@ -1941,7 +1942,8 @@ class _EvaluateVisitor
     } else if (condition is SupportsInterpolation) {
       return await _evaluateToCss(condition.expression, quote: false);
     } else if (condition is SupportsDeclaration) {
-      return "(${await _evaluateToCss(condition.name)}: "
+      return "(${await _evaluateToCss(condition.name)}:"
+          "${condition.isCustomProperty ? '' : ' '}"
           "${await _evaluateToCss(condition.value)})";
     } else if (condition is SupportsFunction) {
       return "${await _performInterpolation(condition.name)}("

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: 96397ede2c79b09005bbac9a013d4a6b42faf736
+// Checksum: c1d303225e5cac5e32dd32a4eed30a71a35b390c
 //
 // ignore_for_file: unused_import
 
@@ -1653,7 +1653,8 @@ class _EvaluateVisitor
     var url = _interpolationToValue(import.url);
     var supports = import.supports.andThen((supports) {
       var arg = supports is SupportsDeclaration
-          ? "${_evaluateToCss(supports.name)}: "
+          ? "${_evaluateToCss(supports.name)}:"
+              "${supports.isCustomProperty ? '' : ' '}"
               "${_evaluateToCss(supports.value)}"
           : supports.andThen(_visitSupportsCondition);
       return CssValue("supports($arg)", supports.span);
@@ -1934,7 +1935,8 @@ class _EvaluateVisitor
     } else if (condition is SupportsInterpolation) {
       return _evaluateToCss(condition.expression, quote: false);
     } else if (condition is SupportsDeclaration) {
-      return "(${_evaluateToCss(condition.name)}: "
+      return "(${_evaluateToCss(condition.name)}:"
+          "${condition.isCustomProperty ? '' : ' '}"
           "${_evaluateToCss(condition.value)})";
     } else if (condition is SupportsFunction) {
       return "${_performInterpolation(condition.name)}("