Unify strings and identifiers.

The separation makes sense conceptually, but it would make string
functions a lot harder to write.

lib/src/ast/sass.dart

@@ -12,7 +12,6 @@ export 'sass/expression/binary_operation.dart';
 export 'sass/expression/boolean.dart';
 export 'sass/expression/color.dart';
 export 'sass/expression/function.dart';
-export 'sass/expression/identifier.dart';
 export 'sass/expression/list.dart';
 export 'sass/expression/map.dart';
 export 'sass/expression/null.dart';

lib/src/ast/sass/expression/identifier.dart

@@ -1,22 +0,0 @@
-// Copyright 2016 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/expression.dart';
-import '../expression.dart';
-import '../interpolation.dart';
-
-class IdentifierExpression implements Expression {
-  final Interpolation text;
-
-  FileSpan get span => text.span;
-
-  IdentifierExpression(this.text);
-
-  /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>
-      visitor.visitIdentifierExpression(this);
-
-  String toString() => text.toString();
-}

lib/src/ast/sass/expression/string.dart

@@ -19,24 +19,28 @@ class StringExpression implements Expression {
   /// included.
   final Interpolation text;
 
+  final bool hasQuotes;
+
   FileSpan get span => text.span;
 
   static String quoteText(String text) =>
-      new StringExpression(new Interpolation([text], null))
+      new StringExpression(new Interpolation([text], null), quotes: true)
           .asInterpolation(static: true)
           .asPlain;
 
-  StringExpression(this.text);
+  StringExpression(this.text, {bool quotes}) : hasQuotes = quotes;
 
   /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>
       visitor.visitStringExpression(this);
 
   /// Interpolation that, when evaluated, produces the syntax of the string.
   ///
-  /// Unlike [text], his doesn't resolve escapes and does include quotes.
+  /// Unlike [text], his doesn't resolve escapes and does include quotes for
+  /// quoted strings.
   Interpolation asInterpolation({bool static: false, int quote}) {
-    quote ??= _bestQuote();
-    var buffer = new InterpolationBuffer()..writeCharCode(quote);
+    quote ??= hasQuotes ? null : _bestQuote();
+    var buffer = new InterpolationBuffer();
+    if (quote != null) buffer.writeCharCode(quote);
     for (var value in text.contents) {
       if (value is Interpolation) {
         buffer.addInterpolation(value);
@@ -63,7 +67,7 @@ class StringExpression implements Expression {
         }
       }
     }
-    buffer.writeCharCode(quote);
+    if (quote != null) buffer.writeCharCode(quote);
 
     return buffer.interpolation(text.span);
   }

lib/src/ast/selector/list.dart

@@ -31,7 +31,7 @@ class SelectorList extends Selector {
     return new SassList(components.map((complex) {
       return new SassList(
           complex.components
-              .map((component) => new SassIdentifier(component.toString())),
+              .map((component) => new SassString(component.toString())),
           ListSeparator.space);
     }), ListSeparator.comma);
   }

lib/src/functions.dart

@@ -11,5 +11,5 @@ void defineCoreFunctions(Environment environment) {
   environment.setFunction(new BuiltInCallable(
       "inspect",
       new ArgumentDeclaration([new Argument("value")]),
-      (arguments) => new SassIdentifier(arguments.single.toString())));
+      (arguments) => new SassString(arguments.single.toString())));
 }

lib/src/parse/stylesheet.dart

@@ -101,7 +101,8 @@ abstract class StylesheetParser extends Parser {
 
   Expression _declarationExpression() {
     if (lookingAtChildren()) {
-      return new StringExpression(new Interpolation([], scanner.emptySpan));
+      return new StringExpression(new Interpolation([], scanner.emptySpan),
+          quotes: true);
     }
 
     return _expression();
@@ -1265,7 +1266,8 @@ abstract class StylesheetParser extends Parser {
       }
     }
 
-    return new StringExpression(buffer.interpolation(scanner.spanFrom(start)));
+    return new StringExpression(buffer.interpolation(scanner.spanFrom(start)),
+        quotes: true);
   }
 
   Expression _hexColorOrID() {
@@ -1287,8 +1289,7 @@ abstract class StylesheetParser extends Parser {
     var buffer = new InterpolationBuffer();
     buffer.writeCharCode($hash);
     buffer.addInterpolation(identifier);
-    return new IdentifierExpression(
-        buffer.interpolation(scanner.spanFrom(start)));
+    return new StringExpression(buffer.interpolation(scanner.spanFrom(start)));
   }
 
   SassColor _hexColorContents() {
@@ -1342,7 +1343,7 @@ abstract class StylesheetParser extends Parser {
 
     return scanner.peekChar() == $lparen
         ? new FunctionExpression(identifier, _argumentInvocation())
-        : new IdentifierExpression(identifier);
+        : new StringExpression(identifier);
   }
 
   /// Consumes tokens up to "{", "}", ";", or "!".
@@ -1420,7 +1421,7 @@ abstract class StylesheetParser extends Parser {
     return buffer.interpolation(scanner.spanFrom(start));
   }
 
-  IdentifierExpression _interpolatedDeclarationValue() {
+  StringExpression _interpolatedDeclarationValue() {
     // NOTE: this logic is largely duplicated in Parser.declarationValue. Most
     // changes here should be mirrored there.
 
@@ -1511,8 +1512,7 @@ abstract class StylesheetParser extends Parser {
     }
 
     if (brackets.isNotEmpty) scanner.expectChar(brackets.last);
-    return new IdentifierExpression(
-        buffer.interpolation(scanner.spanFrom(start)));
+    return new StringExpression(buffer.interpolation(scanner.spanFrom(start)));
   }
 
   Interpolation _interpolatedIdentifier() {

lib/src/value.dart

@@ -4,14 +4,12 @@
 
 import 'exception.dart';
 import 'value/boolean.dart';
-import 'value/identifier.dart';
 import 'value/string.dart';
 import 'visitor/interface/value.dart';
 import 'visitor/serialize.dart';
 
 export 'value/boolean.dart';
 export 'value/color.dart';
-export 'value/identifier.dart';
 export 'value/list.dart';
 export 'value/map.dart';
 export 'value/null.dart';
@@ -56,23 +54,24 @@ abstract class Value {
 
   Value plus(Value other) {
     if (other is SassString) {
-      return new SassString(valueToCss(this) + other.text);
+      return new SassString(valueToCss(this) + other.text,
+          quotes: other.hasQuotes);
     } else {
-      return new SassIdentifier(valueToCss(this) + valueToCss(other));
+      return new SassString(valueToCss(this) + valueToCss(other));
     }
   }
 
   Value minus(Value other) =>
-      new SassIdentifier("${valueToCss(this)}-${valueToCss(other)}");
+      new SassString("${valueToCss(this)}-${valueToCss(other)}");
 
   Value dividedBy(Value other) =>
-      new SassIdentifier("${valueToCss(this)}/${valueToCss(other)}");
+      new SassString("${valueToCss(this)}/${valueToCss(other)}");
 
-  Value unaryPlus() => new SassIdentifier("+${valueToCss(this)}");
+  Value unaryPlus() => new SassString("+${valueToCss(this)}");
 
-  Value unaryMinus() => new SassIdentifier("-${valueToCss(this)}");
+  Value unaryMinus() => new SassString("-${valueToCss(this)}");
 
-  Value unaryDivide() => new SassIdentifier("/${valueToCss(this)}");
+  Value unaryDivide() => new SassString("/${valueToCss(this)}");
 
   Value unaryNot() => sassFalse;
 

lib/src/value/identifier.dart

@@ -1,25 +0,0 @@
-// Copyright 2016 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 '../visitor/interface/value.dart';
-import '../value.dart';
-
-class SassIdentifier extends Value {
-  final String text;
-
-  bool get isBlank => text.isEmpty;
-
-  SassIdentifier(this.text);
-
-  /*=T*/ accept/*<T>*/(ValueVisitor/*<T>*/ visitor) =>
-      visitor.visitIdentifier(this);
-
-  bool operator ==(other) {
-    if (other is SassString) return text == other.text;
-    if (other is SassIdentifier) return text == other.text;
-    return false;
-  }
-
-  int get hashCode => text.hashCode;
-}

lib/src/value/string.dart

@@ -9,19 +9,23 @@ import '../value.dart';
 class SassString extends Value {
   final String text;
 
-  SassString(this.text);
+  final bool hasQuotes;
+
+  SassString(this.text, {bool quotes: false}) : hasQuotes = quotes;
 
   /*=T*/ accept/*<T>*/(ValueVisitor/*<T>*/ visitor) =>
       visitor.visitString(this);
 
-  Value plus(Value other) => new SassString(
-      text + (other is SassString ? other.text : valueToCss(other)));
-
-  bool operator ==(other) {
-    if (other is SassString) return text == other.text;
-    if (other is SassIdentifier) return text == other.text;
-    return false;
+  Value plus(Value other) {
+    if (other is SassString) {
+      return new SassString(text + other.text,
+          quotes: hasQuotes || other.hasQuotes);
+    } else {
+      return new SassString(text + valueToCss(other), quotes: hasQuotes);
+    }
   }
 
+  bool operator ==(other) => other is SassString && text == other.text;
+
   int get hashCode => text.hashCode;
 }

lib/src/visitor/interface/expression.dart

@@ -9,7 +9,6 @@ abstract class ExpressionVisitor<T> {
   T visitBooleanExpression(BooleanExpression node);
   T visitColorExpression(ColorExpression node);
   T visitFunctionExpression(FunctionExpression node);
-  T visitIdentifierExpression(IdentifierExpression node);
   T visitListExpression(ListExpression node);
   T visitMapExpression(MapExpression node);
   T visitNullExpression(NullExpression node);

lib/src/visitor/interface/value.dart

@@ -7,7 +7,6 @@ import '../../value.dart';
 abstract class ValueVisitor<T> {
   T visitBoolean(SassBoolean value);
   T visitColor(SassColor value);
-  T visitIdentifier(SassIdentifier value);
   T visitList(SassList value);
   T visitMap(SassMap value);
   T visitNull(SassNull value);

lib/src/visitor/perform.dart

@@ -629,9 +629,6 @@ class PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
     }
   }
 
-  SassIdentifier visitIdentifierExpression(IdentifierExpression node) =>
-      new SassIdentifier(_performInterpolation(node.text));
-
   SassBoolean visitBooleanExpression(BooleanExpression node) =>
       new SassBoolean(node.value);
 
@@ -695,7 +692,7 @@ 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 SassIdentifier("$name(${arguments.join(', ')})");
+    return new SassString("$name(${arguments.join(', ')})");
   }
 
   Value _runUserDefinedCallable(CallableInvocation invocation,
@@ -805,9 +802,7 @@ class PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
 
   void _addRestMap(Map<String, Value> values, SassMap map, FileSpan span) {
     map.contents.forEach((key, value) {
-      if (key is SassIdentifier) {
-        values[key.text] = value;
-      } else if (key is SassString) {
+      if (key is SassString) {
         values[key.text] = value;
       } else {
         throw _exception(
@@ -863,7 +858,7 @@ class PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
   }
 
   SassString visitStringExpression(StringExpression node) =>
-      new SassString(_performInterpolation(node.text));
+      new SassString(_performInterpolation(node.text), quotes: node.hasQuotes);
 
   // ## Utilities
 

lib/src/visitor/serialize.dart

@@ -161,7 +161,7 @@ class _SerializeCssVisitor
   }
 
   void _writeCustomPropertyValue(CssDeclaration node) {
-    var value = (node.value.value as SassIdentifier).text;
+    var value = (node.value.value as SassString).text;
 
     var minimumIndentation = _minimumIndentation(value);
     if (minimumIndentation == null) {
@@ -234,9 +234,6 @@ class _SerializeCssVisitor
     _buffer.writeCharCode(hexCharFor(color & 0xF));
   }
 
-  void visitIdentifier(SassIdentifier value) =>
-      _buffer.write(value.text.replaceAll("\n", " "));
-
   void visitList(SassList value) {
     if (value.isBracketed) {
       _buffer.writeCharCode($lbracket);
@@ -301,8 +298,11 @@ class _SerializeCssVisitor
     _buffer.write(value.value.toString());
   }
 
-  void visitString(SassString string) =>
-      _buffer.write(_visitString(string.text));
+  void visitString(SassString string) {
+    _buffer.write(string.hasQuotes
+        ? _visitString(string.text)
+        : string.text.replaceAll("\n", " "));
+  }
 
   String _visitString(String string, {bool forceDoubleQuote: false}) {
     var includesSingleQuote = false;