Make (most) spans mandatory.

Arguments are still optional since they may be constructed for
user-defined arguments.

lib/src/ast/css/at_rule.dart

@@ -17,7 +17,7 @@ class CssAtRule extends CssParentNode {
 
   final FileSpan span;
 
-  CssAtRule(this.name, {bool childless: false, this.value, this.span})
+  CssAtRule(this.name, this.span, {bool childless: false, this.value})
       : isChildless = childless;
 
   /*=T*/ accept/*<T>*/(CssVisitor/*<T>*/ visitor) =>

lib/src/ast/css/comment.dart

@@ -12,7 +12,7 @@ class CssComment extends CssNode {
 
   final FileSpan span;
 
-  CssComment(this.text, {this.span});
+  CssComment(this.text, this.span);
 
   /*=T*/ accept/*<T>*/(CssVisitor/*<T>*/ visitor) =>
       visitor.visitComment(this);

lib/src/ast/css/declaration.dart

@@ -18,7 +18,7 @@ class CssDeclaration extends CssNode {
 
   bool get isCustomProperty => name.value.startsWith("--");
 
-  CssDeclaration(this.name, this.value, {this.span});
+  CssDeclaration(this.name, this.value, this.span);
 
   /*=T*/ accept/*<T>*/(CssVisitor/*<T>*/ visitor) =>
       visitor.visitDeclaration(this);

lib/src/ast/css/media_rule.dart

@@ -13,7 +13,7 @@ class CssMediaRule extends CssParentNode {
 
   final FileSpan span;
 
-  CssMediaRule(this.queries, {this.span});
+  CssMediaRule(this.queries, this.span);
 
   /*=T*/ accept/*<T>*/(CssVisitor/*<T>*/ visitor) =>
       visitor.visitMediaRule(this);

lib/src/ast/css/style_rule.dart

@@ -14,7 +14,7 @@ class CssStyleRule extends CssParentNode {
 
   final FileSpan span;
 
-  CssStyleRule(this.selector, {this.span});
+  CssStyleRule(this.selector, this.span);
 
   /*=T*/ accept/*<T>*/(CssVisitor/*<T>*/ visitor) =>
       visitor.visitStyleRule(this);

lib/src/ast/css/stylesheet.dart

@@ -10,7 +10,7 @@ import 'node.dart';
 class CssStylesheet extends CssParentNode {
   final FileSpan span;
 
-  CssStylesheet({this.span});
+  CssStylesheet(this.span);
 
   /*=T*/ accept/*<T>*/(CssVisitor/*<T>*/ visitor) =>
       visitor.visitStylesheet(this);

lib/src/ast/css/value.dart

@@ -11,7 +11,7 @@ class CssValue<T> implements AstNode {
 
   final FileSpan span;
 
-  CssValue(this.value, {this.span});
+  CssValue(this.value, this.span);
 
   String toString() => value.toString();
 }

lib/src/ast/sass/argument_invocation.dart

@@ -19,13 +19,13 @@ class ArgumentInvocation implements SassNode {
   final FileSpan span;
 
   ArgumentInvocation(Iterable<Expression> positional,
-      Map<String, Expression> named, {this.rest, this.keywordRest, this.span})
+      Map<String, Expression> named, this.span, {this.rest, this.keywordRest})
       : positional = new List.unmodifiable(positional),
         named = new Map.unmodifiable(named) {
     assert(rest != null || keywordRest == null);
   }
 
-  ArgumentInvocation.empty({this.span})
+  ArgumentInvocation.empty(this.span)
     : positional = const [],
       named = const {},
       rest = null,

lib/src/ast/sass/callable_declaration.dart

@@ -17,6 +17,6 @@ abstract class CallableDeclaration implements Statement {
   final FileSpan span;
 
   CallableDeclaration(this.name, this.arguments, Iterable<Statement> children,
-      {this.span})
+      this.span)
       : children = new List.unmodifiable(children);
 }

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

@@ -12,7 +12,7 @@ class BooleanExpression implements Expression {
 
   final FileSpan span;
 
-  BooleanExpression(this.value, {this.span});
+  BooleanExpression(this.value, this.span);
 
   /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>
       visitor.visitBooleanExpression(this);

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

@@ -13,7 +13,7 @@ class ColorExpression implements Expression {
 
   final FileSpan span;
 
-  ColorExpression(this.value, {this.span});
+  ColorExpression(this.value, this.span);
 
   /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>
       visitor.visitColorExpression(this);

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

@@ -21,7 +21,7 @@ class ListExpression implements Expression {
   final FileSpan span;
 
   ListExpression(Iterable<Expression> contents, ListSeparator separator,
-          {bool bracketed: false, FileSpan span})
+      {bool bracketed: false, FileSpan span})
       : this._(new List.unmodifiable(contents), separator, bracketed, span);
 
   ListExpression._(List<Expression> contents, this.separator, this.isBracketed,

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

@@ -13,7 +13,7 @@ class MapExpression implements Expression {
 
   final FileSpan span;
 
-  MapExpression(Iterable<Pair<Expression, Expression>> pairs, {this.span})
+  MapExpression(Iterable<Pair<Expression, Expression>> pairs, this.span)
       : pairs = new List.unmodifiable(pairs);
 
   /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>

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

@@ -12,7 +12,7 @@ class NumberExpression implements Expression {
 
   final FileSpan span;
 
-  NumberExpression(this.value, {this.span});
+  NumberExpression(this.value, this.span);
 
   /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>
       visitor.visitNumberExpression(this);

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

@@ -15,7 +15,7 @@ class UnaryOperatorExpression implements Expression {
 
   final FileSpan span;
 
-  UnaryOperatorExpression(this.operator, this.operand, {this.span});
+  UnaryOperatorExpression(this.operator, this.operand, this.span);
 
   /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>
       visitor.visitUnaryOperatorExpression(this);

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

@@ -12,7 +12,7 @@ class VariableExpression implements Expression {
 
   final FileSpan span;
 
-  VariableExpression(this.name, {this.span});
+  VariableExpression(this.name, this.span);
 
   /*=T*/ accept/*<T>*/(ExpressionVisitor/*<T>*/ visitor) =>
       visitor.visitVariableExpression(this);

lib/src/ast/sass/interpolation.dart

@@ -24,7 +24,7 @@ class Interpolation implements SassNode {
   /// Returns the plain text before the interpolation, or the empty string.
   String get initialPlain => contents.first is String ? contents.first : '';
 
-  Interpolation(Iterable/*(String|Expression)*/ contents, {this.span})
+  Interpolation(Iterable/*(String|Expression)*/ contents, this.span)
       : contents = new List.unmodifiable(contents) {
     for (var i = 0; i < this.contents.length; i++) {
       if (this.contents[i] is! String && this.contents[i] is! Expression) {

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

@@ -17,7 +17,7 @@ class AtRule implements Statement {
 
   final FileSpan span;
 
-  AtRule(this.name, {this.value, Iterable<Statement> children, this.span})
+  AtRule(this.name, this.span, {this.value, Iterable<Statement> children})
       : children = children == null ? null : new List.unmodifiable(children);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>

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

@@ -14,7 +14,7 @@ class Comment implements Statement {
 
   final FileSpan span;
 
-  Comment(this.text, {bool silent: false, this.span})
+  Comment(this.text, this.span, {bool silent: false})
       : isSilent = silent;
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>

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

@@ -10,7 +10,7 @@ import '../statement.dart';
 class Content implements Statement {
   final FileSpan span;
 
-  Content({this.span});
+  Content(this.span);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>
       visitor.visitContent(this);

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

@@ -18,7 +18,7 @@ class Declaration implements Statement {
 
   final FileSpan span;
 
-  Declaration(this.name, {this.value, Iterable<Statement> children, this.span})
+  Declaration(this.name, this.span, {this.value, Iterable<Statement> children})
       : children = children == null ? null : new List.unmodifiable(children);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>

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

@@ -13,7 +13,7 @@ class ExtendRule implements Statement {
 
   final FileSpan span;
 
-  ExtendRule(this.selector, {this.span});
+  ExtendRule(this.selector, this.span);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>
       visitor.visitExtendRule(this);

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

@@ -11,8 +11,8 @@ import '../statement.dart';
 
 class FunctionDeclaration extends CallableDeclaration {
   FunctionDeclaration(String name, ArgumentDeclaration arguments,
-      Iterable<Statement> children, {FileSpan span})
-      : super(name, arguments, children, span: span);
+      Iterable<Statement> children, FileSpan span)
+      : super(name, arguments, children, span);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>
       visitor.visitFunctionDeclaration(this);

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

@@ -15,7 +15,7 @@ class If implements Statement {
 
   final FileSpan span;
 
-  If(this.expression, Iterable<Statement> children, {this.span})
+  If(this.expression, Iterable<Statement> children, this.span)
       : children = new List.unmodifiable(children);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>

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

@@ -18,8 +18,7 @@ class Include implements Statement, CallableInvocation {
 
   final FileSpan span;
 
-  Include(this.name, this.arguments, {Iterable<Statement> children,
-      this.span})
+  Include(this.name, this.arguments, this.span, {Iterable<Statement> children})
       : children = children == null ? null : new List.unmodifiable(children);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>

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

@@ -16,7 +16,7 @@ class MediaRule implements Statement {
   final FileSpan span;
 
   MediaRule(Iterable<MediaQuery> queries, Iterable<Statement> children,
-      {this.span})
+      this.span)
       : queries = new List.unmodifiable(queries),
         children = new List.unmodifiable(children);
 

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

@@ -13,8 +13,8 @@ class MixinDeclaration extends CallableDeclaration {
   final bool hasContent;
 
   MixinDeclaration(String name, ArgumentDeclaration arguments,
-      Iterable<Statement> children, {this.hasContent: false, FileSpan span})
-      : super(name, arguments, children, span: span);
+      Iterable<Statement> children, FileSpan span, {this.hasContent: false})
+      : super(name, arguments, children, span);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>
       visitor.visitMixinDeclaration(this);

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

@@ -13,7 +13,7 @@ class Return implements Statement {
 
   final FileSpan span;
 
-  Return(this.expression, {this.span});
+  Return(this.expression, this.span);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>
       visitor.visitReturn(this);

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

@@ -15,7 +15,7 @@ class StyleRule implements Statement {
 
   final FileSpan span;
 
-  StyleRule(this.selector, Iterable<Statement> children, {this.span})
+  StyleRule(this.selector, Iterable<Statement> children, this.span)
       : children = new List.unmodifiable(children);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>

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

@@ -12,7 +12,7 @@ class Stylesheet implements Statement {
 
   final FileSpan span;
 
-  Stylesheet(Iterable<Statement> children, {this.span})
+  Stylesheet(Iterable<Statement> children, this.span)
       : children = new List.unmodifiable(children);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>

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

@@ -19,8 +19,8 @@ class VariableDeclaration implements Statement {
 
   final FileSpan span;
 
-  VariableDeclaration(this.name, this.expression, {bool guarded: false,
-          bool global: false, this.span})
+  VariableDeclaration(this.name, this.expression, this.span,
+      {bool guarded: false, bool global: false})
       : isGuarded = guarded,
         isGlobal = global;
 

lib/src/extend/extender.dart

@@ -25,7 +25,7 @@ class Extender {
   final _sources = new Expando<ComplexSelector>();
 
   CssStyleRule addSelector(CssValue<SelectorList> selectorValue,
-      {FileSpan span}) {
+      FileSpan span) {
     var selector = selectorValue.value;
     for (var complex in selector.components) {
       for (var component in complex.components) {
@@ -38,7 +38,7 @@ class Extender {
     }
 
     if (_extensions.isNotEmpty) selector = _extendList(selector, _extensions);
-    var rule = new CssStyleRule(selectorValue, span: span);
+    var rule = new CssStyleRule(selectorValue, span);
 
     for (var complex in selector.components) {
       for (var component in complex.components) {

lib/src/interpolation_buffer.dart

@@ -53,7 +53,7 @@ class InterpolationBuffer implements StringSink {
   Interpolation interpolation([FileSpan span]) {
     var contents = _contents.toList();
     if (_text.isNotEmpty) contents.add(_text.toString());
-    return new Interpolation(contents, span: span);
+    return new Interpolation(contents, span);
   }
 
   String toString() => "${_contents.join('')}$_text";

lib/src/parser.dart

@@ -43,7 +43,7 @@ class Parser {
     var start = _scanner.state;
     var statements = _statements(_topLevelStatement);
     _scanner.expectDone();
-    return new Stylesheet(statements, span: _scanner.spanFrom(start));
+    return new Stylesheet(statements, _scanner.spanFrom(start));
   }
 
   Statement _topLevelStatement() {
@@ -92,16 +92,15 @@ class Parser {
       _ignoreComments();
     }
 
-    return new VariableDeclaration(name, expression,
-        guarded: guarded, global: global, span: _scanner.spanFrom(start));
+    return new VariableDeclaration(name, expression, _scanner.spanFrom(start),
+        guarded: guarded, global: global);
   }
 
   StyleRule _styleRule() {
     var start = _scanner.state;
     var selector = _almostAnyValue();
     var children = _children(_ruleChild);
-    return new StyleRule(selector, children,
-        span: _scanner.spanFrom(start));
+    return new StyleRule(selector, children, _scanner.spanFrom(start));
   }
 
   Statement _ruleChild() {
@@ -111,8 +110,7 @@ class Parser {
 
   Expression _declarationExpression() {
     if (_scanner.peekChar() == $lbrace) {
-      return new StringExpression(
-          new Interpolation([], span: _scanner.emptySpan));
+      return new StringExpression(new Interpolation([], _scanner.emptySpan));
     }
 
     return _expression();
@@ -155,7 +153,7 @@ class Parser {
     var children = _children(_ruleChild);
     return new StyleRule(
         buffer.interpolation(_scanner.spanFrom(start)), children,
-        span: _scanner.spanFrom(start));
+        _scanner.spanFrom(start));
   }
 
   /// Tries to parse a declaration, and returns the value parsed so far if it
@@ -195,7 +193,7 @@ class Parser {
       if (next != $semicolon && next != $rbrace) {
         _scanner.expectChar($semicolon);
       }
-      return new Declaration(name, value: value);
+      return new Declaration(name, _scanner.spanFrom(start), value: value);
     }
 
     if (_scanner.scanChar($colon)) {
@@ -204,9 +202,8 @@ class Parser {
 
     var postColonWhitespace = _commentText();
     if (_scanner.peekChar() == $lbrace) {
-      return new Declaration(name,
-          children: _children(_declarationChild),
-          span: _scanner.spanFrom(start));
+      return new Declaration(name, _scanner.spanFrom(start),
+          children: _children(_declarationChild));
     }
 
     midBuffer.write(postColonWhitespace);
@@ -241,13 +238,11 @@ class Parser {
       return nameBuffer;
     }
 
-    return new Declaration(
-        name,
+    return new Declaration(name, _scanner.spanFrom(start),
         value: value,
         children: _scanner.peekChar() == $lbrace
              ? _children(_declarationChild)
-             : null,
-        span: _scanner.spanFrom(start));
+             : null);
   }
 
   Declaration _declaration() {
@@ -258,19 +253,16 @@ class Parser {
     _ignoreComments();
 
     if (_scanner.peekChar() == $lbrace) {
-      return new Declaration(name,
-          children: _children(_declarationChild),
-          span: _scanner.spanFrom(start));
+      return new Declaration(name, _scanner.spanFrom(start),
+          children: _children(_declarationChild));
     }
 
     var value = _declarationExpression();
-    return new Declaration(
-        name,
+    return new Declaration(name, _scanner.spanFrom(start),
         value: value,
         children: _scanner.peekChar() == $lbrace
              ? _children(_declarationChild)
-             : null,
-        span: _scanner.spanFrom(start));
+             : null);
   }
 
   Statement _declarationChild() {
@@ -340,7 +332,7 @@ class Parser {
   Content _content(LineScannerState start) {
     if (_inMixin) {
       _mixinHasContent = true;
-      return new Content(span: _scanner.spanFrom(start));
+      return new Content(_scanner.spanFrom(start));
     }
 
     _scanner.error(
@@ -351,7 +343,7 @@ class Parser {
   }
 
   ExtendRule _extend(LineScannerState start) =>
-      new ExtendRule(_almostAnyValue(), span: _scanner.spanFrom(start));
+      new ExtendRule(_almostAnyValue(), _scanner.spanFrom(start));
 
   FunctionDeclaration _functionDeclaration(LineScannerState start) {
     var name = _identifier();
@@ -368,19 +360,19 @@ class Parser {
     var children = _children(_functionAtRule);
 
     // TODO: ensure there aren't duplicate argument names.
-    return new FunctionDeclaration(name, arguments, children,
-        span: _scanner.spanFrom(start));
+    return new FunctionDeclaration(
+        name, arguments, children, _scanner.spanFrom(start));
   }
 
   If _if(LineScannerState start, Statement child()) =>
-      new If(_expression(), _children(child), span: _scanner.spanFrom(start));
+      new If(_expression(), _children(child), _scanner.spanFrom(start));
 
   Include _include(LineScannerState start) {
     var name = _identifier();
     _ignoreComments();
     var arguments = _scanner.peekChar() == $lparen
         ? _argumentInvocation()
-        : new ArgumentInvocation.empty(span: _scanner.emptySpan);
+        : new ArgumentInvocation.empty(_scanner.emptySpan);
     _ignoreComments();
 
     List<Statement> children;
@@ -390,13 +382,12 @@ class Parser {
       _inContentBlock = false;
     }
 
-    return new Include(name, arguments,
-        children: children, span: _scanner.spanFrom(start));
+    return new Include(name, arguments, _scanner.spanFrom(start),
+        children: children);
   }
 
-  MediaRule _mediaRule(LineScannerState start) =>
-      new MediaRule(_mediaQueryList(), _children(_ruleChild),
-          span: _scanner.spanFrom(start));
+  MediaRule _mediaRule(LineScannerState start) => new MediaRule(
+      _mediaQueryList(), _children(_ruleChild), _scanner.spanFrom(start));
 
   MixinDeclaration _mixinDeclaration(LineScannerState start) {
     var name = _identifier();
@@ -417,14 +408,14 @@ class Parser {
     var children = _children(_ruleChild);
     _inMixin = false;
 
-    return new MixinDeclaration(name, arguments, children,
-        hasContent: _mixinHasContent,
-        span: _scanner.spanFrom(start));
+    return new MixinDeclaration(
+        name, arguments, children, _scanner.spanFrom(start),
+        hasContent: _mixinHasContent);
   }
 
   Return _return(LineScannerState start) {
     _ignoreComments();
-    return new Return(_expression(), span: _scanner.spanFrom(start));
+    return new Return(_expression(), _scanner.spanFrom(start));
   }
 
   AtRule _unknownAtRule(LineScannerState start, String name) {
@@ -435,10 +426,9 @@ class Parser {
       value = _almostAnyValue();
     }
 
-    return new AtRule(name,
+    return new AtRule(name, _scanner.spanFrom(start),
         value: value,
-        children: _scanner.peekChar() == $lbrace ? _children(_ruleChild) : null,
-        span: _scanner.spanFrom(start));
+        children: _scanner.peekChar() == $lbrace ? _children(_ruleChild) : null);
   }
 
   // This returns [Statement] so that it can be returned within case statements.
@@ -472,14 +462,15 @@ class Parser {
         break;
       }
 
-      arguments.add(new Argument(name,
-          defaultValue: defaultValue, span: _scanner.spanFrom(variableStart)));
+      arguments.add(new Argument(name, span: _scanner.spanFrom(variableStart),
+          defaultValue: defaultValue));
       if (!_scanner.scanChar($comma)) break;
       _ignoreComments();
     }
     _scanner.expectChar($rparen);
     return new ArgumentDeclaration(arguments,
-        restArgument: restArgument, span: _scanner.spanFrom(start));
+        restArgument: restArgument,
+        span: _scanner.spanFrom(start));
   }
 
   // ## Expressions
@@ -522,8 +513,8 @@ class Parser {
     }
     _scanner.expectChar($rparen);
 
-    return new ArgumentInvocation(positional, named,
-        rest: rest, keywordRest: keywordRest, span: _scanner.spanFrom(start));
+    return new ArgumentInvocation(positional, named, _scanner.spanFrom(start),
+        rest: rest, keywordRest: keywordRest);
   }
 
   Expression _expression() {
@@ -562,9 +553,9 @@ class Parser {
       if (!_scanner.scanChar($comma)) break;
     }
 
-    return new ListExpression(expressions, ListSeparator.comma,
-        bracketed: true,
-        span: _scanner.spanFrom(start));
+    return new ListExpression(
+        expressions, ListSeparator.comma,
+        bracketed: true, span: _scanner.spanFrom(start));
   }
 
   Expression _spaceListOrValue() {
@@ -632,8 +623,8 @@ class Parser {
     _ignoreComments();
     if (!_lookingAtExpression()) {
       _scanner.expectChar($rparen);
-      return new ListExpression([], ListSeparator.undecided,
-          span: _scanner.spanFrom(start));
+      return new ListExpression(
+          [], ListSeparator.undecided, span: _scanner.spanFrom(start));
     }
 
     var first = _spaceListOrValue();
@@ -656,8 +647,8 @@ class Parser {
     }
 
     _scanner.expectChar($lparen);
-    return new ListExpression(expressions, ListSeparator.comma,
-        span: _scanner.spanFrom(start));
+    return new ListExpression(
+        expressions, ListSeparator.comma, span: _scanner.spanFrom(start));
   }
 
   MapExpression _map(Expression first, LineScannerState start) {
@@ -675,7 +666,7 @@ class Parser {
     }
 
     _scanner.expectChar($rparen);
-    return new MapExpression(pairs, span: _scanner.spanFrom(start));
+    return new MapExpression(pairs, _scanner.spanFrom(start));
   }
 
   UnaryOperatorExpression _unaryOperator() {
@@ -688,8 +679,8 @@ class Parser {
 
     _ignoreComments();
     var operand = _singleExpression();
-    return new UnaryOperatorExpression(operator, operand,
-        span: _scanner.spanFrom(start));
+    return new UnaryOperatorExpression(
+        operator, operand, _scanner.spanFrom(start));
   }
 
   NumberExpression _number() {
@@ -735,13 +726,12 @@ class Parser {
       number = number * math.pow(10, exponentSign * exponent);
     }
 
-    return new NumberExpression(sign * number, span: _scanner.spanFrom(start));
+    return new NumberExpression(sign * number, _scanner.spanFrom(start));
   }
 
   VariableExpression _variable() {
     var start = _scanner.state;
-    return new VariableExpression(_variableName(),
-        span: _scanner.spanFrom(start));
+    return new VariableExpression(_variableName(), _scanner.spanFrom(start));
   }
 
   StringExpression _string({bool static: false}) {
@@ -787,16 +777,14 @@ class Parser {
 
     var first = _scanner.peekChar();
     if (first != null && isDigit(first)) {
-      return new ColorExpression(_hexColorContents(),
-          span: _scanner.spanFrom(start));
+      return new ColorExpression(_hexColorContents(), _scanner.spanFrom(start));
     }
 
     var afterHash = _scanner.state;
     var identifier = _interpolatedIdentifier();
     if (_isHexColor(identifier)) {
       _scanner.state = afterHash;
-      return new ColorExpression(_hexColorContents(),
-          span: _scanner.spanFrom(start));
+      return new ColorExpression(_hexColorContents(), _scanner.spanFrom(start));
     }
 
     var buffer = new InterpolationBuffer();
@@ -839,10 +827,10 @@ class Parser {
       case "not":
         _ignoreComments();
         return new UnaryOperatorExpression(
-            UnaryOperator.not, _singleExpression(), span: identifier.span);
+            UnaryOperator.not, _singleExpression(), identifier.span);
 
-      case "true": return new BooleanExpression(true, span: identifier.span);
-      case "false": return new BooleanExpression(false, span: identifier.span);
+      case "true": return new BooleanExpression(true, identifier.span);
+      case "false": return new BooleanExpression(false, identifier.span);
     }
 
     return _scanner.peekChar() == $lparen
@@ -1424,8 +1412,7 @@ class Parser {
   Interpolation _mediaExpression() {
     if (_scanner.peekChar() == $hash) {
       var interpolation = _singleInterpolation();
-      return new Interpolation([interpolation],
-          span: interpolation.span);
+      return new Interpolation([interpolation], interpolation.span);
     }
 
     var start = _scanner.state;
@@ -1484,9 +1471,9 @@ class Parser {
       _whitespace();
     } while (_scanner.scan("//"));
 
-    return new Comment(_scanner.substring(start.position),
-        silent: true,
-        span: _scanner.spanFrom(start));
+    return new Comment(
+        _scanner.substring(start.position), _scanner.spanFrom(start),
+        silent: true);
   }
 
   Comment _loudComment() {
@@ -1496,9 +1483,9 @@ class Parser {
       while (_scanner.readChar() != $asterisk) {}
     } while (_scanner.readChar() != $slash);
 
-    return new Comment(_scanner.substring(start.position),
-        silent: false,
-        span: _scanner.spanFrom(start));
+    return new Comment(
+        _scanner.substring(start.position), _scanner.spanFrom(start),
+        silent: false);
   }
 
   void _whitespace() {

lib/src/visitor/perform.dart

@@ -53,7 +53,7 @@ class PerformVisitor extends StatementVisitor
   // ## Statements
 
   CssStylesheet visitStylesheet(Stylesheet node) {
-    _root = new CssStylesheet(span: node.span);
+    _root = new CssStylesheet(node.span);
     _parent = _root;
     super.visitStylesheet(node);
     return _root;
@@ -61,7 +61,7 @@ class PerformVisitor extends StatementVisitor
 
   void visitComment(Comment node) {
     if (node.isSilent) return;
-    _parent.addChild(new CssComment(node.text, span: node.span));
+    _parent.addChild(new CssComment(node.text, node.span));
   }
 
   void visitContent(Content node) {
@@ -78,7 +78,7 @@ class PerformVisitor extends StatementVisitor
   void visitDeclaration(Declaration node) {
     var name = _interpolationToValue(node.name);
     if (_declarationName != null) {
-      name = new CssValue("$_declarationName-${name.value}", span: name.span);
+      name = new CssValue("$_declarationName-${name.value}", name.span);
     }
     var cssValue = node.value == null ? null : _performExpression(node.value);
 
@@ -86,7 +86,7 @@ class PerformVisitor extends StatementVisitor
     // will throw an error that we want the user to see.
     if (cssValue != null &&
         (!cssValue.value.isBlank || cssValue.value is SassList)) {
-      _parent.addChild(new CssDeclaration(name, cssValue, span: node.span));
+      _parent.addChild(new CssDeclaration(name, cssValue, node.span));
     }
 
     if (node.children != null) {
@@ -121,12 +121,12 @@ class PerformVisitor extends StatementVisitor
         : _interpolationToValue(node.value, trim: true);
 
     if (node.children == null) {
-      _parent.addChild(new CssAtRule(node.name,
-          childless: true, value: value, span: node.span));
+      _parent.addChild(new CssAtRule(node.name, node.span,
+          childless: true, value: value));
       return;
     }
 
-    _withParent(new CssAtRule(node.name, value: value, span: node.span), () {
+    _withParent(new CssAtRule(node.name, node.span, value: value), () {
       if (_selector == null) {
         super.visitAtRule(node);
       } else {
@@ -135,7 +135,7 @@ class PerformVisitor extends StatementVisitor
         //
         // For example, "a {@foo {b: c}}" should produce "@foo {a {b: c}}".
         _withParent(
-            new CssStyleRule(_selector),
+            new CssStyleRule(_selector, _selector.span),
             () => super.visitAtRule(node),
             removeIfEmpty: true);
       }
@@ -197,7 +197,7 @@ class PerformVisitor extends StatementVisitor
         : _mergeMediaQueries(_mediaQueries, queryIterable);
     if (queries.isEmpty) return;
 
-    _withParent(new CssMediaRule(queries, span: node.span), () {
+    _withParent(new CssMediaRule(queries, node.span), () {
       _withMediaQueries(queries, () {
         if (_selector == null) {
           super.visitMediaRule(node);
@@ -208,7 +208,7 @@ class PerformVisitor extends StatementVisitor
           // For example, "a {@media screen {b: c}}" should produce
           // "@media screen {a {b: c}}".
           _withParent(
-              new CssStyleRule(_selector),
+              new CssStyleRule(_selector, _selector.span),
               () => super.visitMediaRule(node),
               removeIfEmpty: true);
         }
@@ -257,11 +257,11 @@ class PerformVisitor extends StatementVisitor
 
     // TODO: catch errors and re-contextualize them relative to
     // [node.selector.span.start].
-    var selector = new CssValue<SelectorList>(parsedSelector,
-        span: node.selector.span);
+    var selector = new CssValue<SelectorList>(
+        parsedSelector, node.selector.span);
 
     _withParent(
-        _extender.addSelector(selector, span: node.span),
+        _extender.addSelector(selector, node.span),
         () => _withSelector(selector, () => super.visitStyleRule(node)),
         through: (node) => node is CssStyleRule,
         removeIfEmpty: true);
@@ -523,8 +523,7 @@ class PerformVisitor extends StatementVisitor
   CssValue<String> _interpolationToValue(
       Interpolation interpolation, {bool trim: false}) {
     var result = _performInterpolation(interpolation);
-    return new CssValue(trim ? result.trim() : result,
-        span: interpolation.span);
+    return new CssValue(trim ? result.trim() : result, interpolation.span);
   }
 
   String _performInterpolation(Interpolation interpolation) {
@@ -535,7 +534,7 @@ class PerformVisitor extends StatementVisitor
   }
 
   CssValue<Value> _performExpression(Expression expression) =>
-      new CssValue(expression.accept(this), span: expression.span);
+      new CssValue(expression.accept(this), expression.span);
 
   /*=T*/ _withParent/*<S extends CssParentNode, T>*/(
       /*=S*/ node, /*=T*/ callback(),