Add Value.toCssString().

lib/src/functions.dart

@@ -14,7 +14,6 @@ import 'extend/extender.dart';
 import 'util/number.dart';
 import 'utils.dart';
 import 'value.dart';
-import 'visitor/serialize.dart';
 
 /// A regular expression matching the beginning of a proprietary Microsoft
 /// filter declaration.
@@ -42,9 +41,7 @@ void defineCoreFunctions(Environment environment) {
 
   environment.defineFunction("rgb", r"$red, $green, $blue", (arguments) {
     if (arguments[0].isCalc || arguments[1].isCalc || arguments[2].isCalc) {
-      return new SassString(
+      return _functionString('rgb', arguments);
-          "rgb(${valueToCss(arguments[0])}, ${valueToCss(arguments[0])}, "
-          "${valueToCss(arguments[0])})");
     }
 
     var red = arguments[0].assertNumber("red");
@@ -66,9 +63,7 @@ void defineCoreFunctions(Environment environment) {
           arguments[1].isCalc ||
           arguments[2].isCalc ||
           arguments[3].isCalc) {
-        return new SassString(
+        return _functionString('rgba', arguments);
-            "rgba(${valueToCss(arguments[0])}, ${valueToCss(arguments[1])}, "
-            "${valueToCss(arguments[2])}, ${valueToCss(arguments[3])})");
       }
 
       var red = arguments[0].assertNumber("red");
@@ -88,7 +83,7 @@ void defineCoreFunctions(Environment environment) {
       if (arguments[1].isCalc) {
         return new SassString(
             "rgba(${color.red}, ${color.green}, ${color.blue}, "
-            "${valueToCss(arguments[1])})");
+            "${arguments[1].toCssString()})");
       }
 
       var alpha = arguments[0].assertNumber("alpha");
@@ -121,9 +116,7 @@ void defineCoreFunctions(Environment environment) {
   environment.defineFunction("hsl", r"$hue, $saturation, $lightness",
       (arguments) {
     if (arguments[0].isCalc || arguments[1].isCalc || arguments[2].isCalc) {
-      return new SassString(
+      return _functionString("hsl", arguments);
-          "rgb(${valueToCss(arguments[0])}, ${valueToCss(arguments[0])}, "
-          "${valueToCss(arguments[0])})");
     }
 
     var hue = arguments[0].assertNumber("hue");
@@ -139,9 +132,7 @@ void defineCoreFunctions(Environment environment) {
         arguments[1].isCalc ||
         arguments[2].isCalc ||
         arguments[3].isCalc) {
-      return new SassString(
+      return _functionString("hsla", arguments);
-          "rgba(${valueToCss(arguments[0])}, ${valueToCss(arguments[1])}, "
-          "${valueToCss(arguments[2])}, ${valueToCss(arguments[3])})");
     }
 
     var hue = arguments[0].assertNumber("hue");
@@ -207,7 +198,7 @@ void defineCoreFunctions(Environment environment) {
 
   environment.defineFunction("grayscale", r"$color", (arguments) {
     if (arguments[0] is SassNumber) {
-      return new SassString("grayscale(${valueToCss(arguments[0])})");
+      return _functionString('grayscale', arguments);
     }
 
     var color = arguments[0].assertColor("color");
@@ -223,7 +214,7 @@ void defineCoreFunctions(Environment environment) {
     if (arguments[0] is SassNumber) {
       // TODO: find some way of ensuring this is stringified using the right
       // options. We may need to resort to zones.
-      return new SassString("invert(${valueToCss(arguments[0])})");
+      return _functionString("invert", arguments);
     }
 
     var color = arguments[0].assertColor("color");
@@ -247,7 +238,7 @@ void defineCoreFunctions(Environment environment) {
           !argument.hasQuotes &&
           argument.text.contains(_microsoftFilterStart)) {
         // Suport the proprietary Microsoft alpha() function.
-        return new SassString("alpha(${valueToCss(argument)})");
+        return _functionString("alpha", arguments);
       }
 
       var color = argument.assertColor("color");
@@ -259,7 +250,7 @@ void defineCoreFunctions(Environment environment) {
           !argument.hasQuotes &&
           argument.text.contains(_microsoftFilterStart))) {
         // Suport the proprietary Microsoft alpha() function.
-        return new SassString("alpha(${arguments.map(valueToCss).join(', ')})");
+        return _functionString("alpha", arguments);
       }
 
       assert(arguments.length != 1);
@@ -270,7 +261,7 @@ void defineCoreFunctions(Environment environment) {
 
   environment.defineFunction("opacity", r"$color", (arguments) {
     if (arguments[0] is SassNumber) {
-      return new SassString("opacity(${valueToCss(arguments[0])})");
+      return _functionString("opacity", arguments);
     }
 
     var color = arguments[0].assertColor("color");
@@ -894,6 +885,13 @@ void defineCoreFunctions(Environment environment) {
   });
 }
 
+/// Returns a string representation of [name] called with [arguments], as though
+/// it were a plain CSS function.
+SassString _functionString(String name, List<Value> arguments) =>
+    new SassString("$name(" +
+        arguments.map((argument) => argument.toCssString()).join(', ') +
+        ")");
+
 /// Asserts that [number] is a percentage or has no units, and normalizes the
 /// value.
 ///

lib/src/value.dart

@@ -254,37 +254,44 @@ abstract class Value {
   /// The SassScript `+` operation.
   Value plus(Value other) {
     if (other is SassString) {
-      return new SassString(valueToCss(this) + other.text,
+      return new SassString(toCssString() + other.text,
           quotes: other.hasQuotes);
     } else {
-      return new SassString(valueToCss(this) + valueToCss(other));
+      return new SassString(toCssString() + other.toCssString());
     }
   }
 
   /// The SassScript `-` operation.
   Value minus(Value other) =>
-      new SassString("${valueToCss(this)}-${valueToCss(other)}");
+      new SassString("${toCssString()}-${other.toCssString()}");
 
   /// The SassScript `/` operation.
   Value dividedBy(Value other) =>
-      new SassString("${valueToCss(this)}/${valueToCss(other)}");
+      new SassString("${toCssString()}/${other.toCssString()}");
 
   /// The SassScript unary `+` operation.
-  Value unaryPlus() => new SassString("+${valueToCss(this)}");
+  Value unaryPlus() => new SassString("+${toCssString()}");
 
   /// The SassScript unary `-` operation.
-  Value unaryMinus() => new SassString("-${valueToCss(this)}");
+  Value unaryMinus() => new SassString("-${toCssString()}");
 
   /// The SassScript unary `/` operation.
-  Value unaryDivide() => new SassString("/${valueToCss(this)}");
+  Value unaryDivide() => new SassString("/${toCssString()}");
 
   /// The SassScript unary `not` operation.
   Value unaryNot() => sassFalse;
 
+  /// Returns a valid CSS representation of [this].
+  ///
+  /// Throws a [SassScriptException] if [this] can't be represented in plain
+  /// CSS. Use [toString] instead to get a string representation even if this
+  /// isn't valid CSS.
+  String toCssString() => valueToCss(this);
+
   /// Returns a string representation of [this].
   ///
   /// Note that this is equivalent to calling `inspect()` on the value, and thus
-  /// won't reflect the user's output settings. [valueToCss] should be used
+  /// won't reflect the user's output settings. [toCssString] should be used
   /// instead to convert [this] to CSS.
   String toString() => valueToCss(this, inspect: true);
 

lib/src/value/string.dart

@@ -5,7 +5,6 @@
 import 'package:charcode/charcode.dart';
 
 import '../visitor/interface/value.dart';
-import '../visitor/serialize.dart';
 import '../value.dart';
 
 /// A SassScript string.
@@ -44,7 +43,7 @@ class SassString extends Value {
       return new SassString(text + other.text,
           quotes: hasQuotes || other.hasQuotes);
     } else {
-      return new SassString(text + valueToCss(other), quotes: hasQuotes);
+      return new SassString(text + other.toCssString(), quotes: hasQuotes);
     }
   }
 

lib/src/visitor/perform.dart

@@ -21,7 +21,6 @@ import '../utils.dart';
 import '../value.dart';
 import 'interface/statement.dart';
 import 'interface/expression.dart';
-import 'serialize.dart';
 
 /// A function that takes a callback with no arguments.
 typedef _ScopeCallback(callback());
@@ -597,10 +596,10 @@ class _PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
     } else if (condition is SupportsNegation) {
       return "not ${_parenthesize(condition.condition)}";
     } else if (condition is SupportsInterpolation) {
-      return valueToCss(condition.expression.accept(this));
+      return condition.expression.accept(this).toCssString();
     } else if (condition is SupportsDeclaration) {
-      return "(${valueToCss(condition.name.accept(this))}: "
+      return "(${condition.name.accept(this).toCssString()}: "
-          "${valueToCss(condition.value.accept(this))})";
+          "${condition.value.accept(this).toCssString()})";
     } else {
       return null;
     }
@@ -631,7 +630,7 @@ class _PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
     _addExceptionSpan(
         node.span,
         () => stderr
-            .writeln("WARNING: ${valueToCss(node.expression.accept(this))}"));
+            .writeln("WARNING: ${node.expression.accept(this).toCssString()}"));
     for (var line in _stackTrace(node.span).toString().split("\n")) {
       stderr.writeln("         $line");
     }
@@ -789,7 +788,9 @@ class _PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
     // TODO: if rest is an arglist that has keywords, error out.
     var rest = node.arguments.rest?.accept(this);
     if (rest != null) arguments.add(rest);
-    return new SassString("$name(${arguments.map(valueToCss).join(', ')})");
+    return new SassString("$name(" +
+        arguments.map((argument) => argument.toCssString()).join(', ') +
+        ")");
   }
 
   /// Evaluates the arguments in [invocation] as applied to [callable], and