Merge branch 'null-literal'

Closes #374

doc-src/SASS_REFERENCE.md

@@ -627,12 +627,13 @@ this still works, but it's deprecated and prints a warning.
 
 ### Data Types
 
-SassScript supports four main data types:
+SassScript supports six main data types:
 
 * numbers (e.g. `1.2`, `13`, `10px`)
 * strings of text, with and without quotes (e.g. `"foo"`, `'bar'`, `baz`)
 * colors (e.g. `blue`, `#04a3f9`, `rgba(255, 0, 0, 0.5)`)
 * booleans (e.g. `true`, `false`)
+* nulls (e.g. `null`)
 * lists of values, separated by spaces or commas (e.g. `1.5em 1em 0 2em`, `Helvetica, Arial, sans-serif`)
 
 SassScript also supports all other types of CSS property value,
@@ -708,8 +709,10 @@ Lists can also have no items in them at all.
 These lists are represented as `()`.
 They can't be output directly to CSS;
 if you try to do e.g. `font-family: ()`, Sass will raise an error.
-If a list contains empty lists, as in `1px 2px () 3px`,
-the empty list will be removed before it's turned into CSS.
+If a list contains empty lists or null values,
+as in `1px 2px () 3px` or `1px 2px null 3px`,
+the empty lists and null values will be removed
+before the containing list is turned into CSS.
 
 ### Operations
 
@@ -932,6 +935,19 @@ is compiled to:
     p:before {
       content: "I ate 15 pies!"; }
 
+Null values are treated as empty strings for string operations and interpolations:
+
+    $value: null;
+    p:before {
+      content: "I ate #{$value} pies!";
+      font-family: sans- + $value; }
+
+is compiled to:
+
+    p:before {
+      content: "I ate  pies!";
+      font-family: sans-; }
+
 #### Boolean Operations
 
 SassScript supports `and`, `or`, and `not` operators
@@ -1046,6 +1062,20 @@ is compiled to:
       content: "First content";
       new-content: "First time reference"; }
 
+Variables with `null` values are treated as unassigned by !default:
+
+    $content: null;
+    $content: "Non-null content" !default;
+
+    #main {
+      content: $content;
+    }
+
+is compiled to:
+
+    #main {
+      content: "Non-null content"; }
+
 ## `@`-Rules and Directives {#directives}
 
 Sass supports all CSS3 `@`-rules,

lib/sass/engine.rb

@@ -600,7 +600,14 @@ def parse_property(name, parsed_name, value, prop, line)
       else
         expr = parse_script(value, :offset => line.offset + line.text.index(value))
       end
-      Tree::PropNode.new(parse_interp(name), expr, prop)
+      node = Tree::PropNode.new(parse_interp(name), expr, prop)
+      if value.strip.empty? && line.children.empty?
+        raise SyntaxError.new(
+          "Invalid property: \"#{node.declaration}\" (no value)." +
+          node.pseudo_class_selector_message)
+      end
+
+      node
     end
 
     def parse_variable(line)

lib/sass/script/lexer.rb

@@ -90,6 +90,7 @@ class Lexer
         :number => /(-)?(?:(\d*\.\d+)|(\d+))([a-zA-Z%]+)?/,
         :color => HEXCOLOR,
         :bool => /(true|false)\b/,
+        :null => /null\b/,
         :ident_op => %r{(#{Regexp.union(*IDENT_OP_NAMES.map{|s| Regexp.new(Regexp.escape(s) + "(?!#{NMCHAR}|\Z)")})})},
         :op => %r{(#{Regexp.union(*OP_NAMES)})},
       }
@@ -234,7 +235,7 @@ def token
         end
 
         variable || string(:double, false) || string(:single, false) || number ||
-          color || bool || string(:uri, false) || raw(UNICODERANGE) ||
+          color || bool || null || string(:uri, false) || raw(UNICODERANGE) ||
           special_fun || special_val || ident_op || ident || op
       end
 
@@ -292,6 +293,11 @@ def bool
         [:bool, Script::Bool.new(s == 'true')]
       end
 
+      def null
+        return unless scan(REGULAR_EXPRESSIONS[:null])
+        [:null, Script::Null.new]
+      end
+
       def special_fun
         return unless str1 = scan(/((-[\w-]+-)?(calc|element)|expression|progid:[a-z\.]*)\(/i)
         str2, _ = Sass::Shared.balance(@scanner, ?(, ?), 1)

lib/sass/script/list.rb

@@ -41,14 +41,14 @@ def eq(other)
     # @see Node#to_s
     def to_s(opts = {})
       raise Sass::SyntaxError.new("() isn't a valid CSS value.") if value.empty?
-      return value.reject {|e| e.is_a?(List) && e.value.empty?}.map {|e| e.to_s(opts)}.join(sep_str)
+      return value.reject {|e| e.is_a?(Null) || e.is_a?(List) && e.value.empty?}.map {|e| e.to_s(opts)}.join(sep_str)
     end
 
     # @see Node#to_sass
     def to_sass(opts = {})
       return "()" if value.empty?
       precedence = Sass::Script::Parser.precedence_of(separator)
-      value.map do |v|
+      value.reject {|e| e.is_a?(Null)}.map do |v|
         if v.is_a?(List) && Sass::Script::Parser.precedence_of(v.separator) <= precedence
           "(#{v.to_sass(opts)})"
         else

lib/sass/script/literal.rb

@@ -9,6 +9,7 @@ class Literal < Node
     require 'sass/script/number'
     require 'sass/script/color'
     require 'sass/script/bool'
+    require 'sass/script/null'
     require 'sass/script/list'
 
     # Returns the Ruby value of the literal.
@@ -217,6 +218,13 @@ def to_s(opts = {})
     end
     alias_method :to_sass, :to_s
 
+    # Returns whether or not this object is null.
+    #
+    # @return [Boolean] `false`
+    def null?
+      false
+    end
+
     protected
 
     # Evaluates the literal.

lib/sass/script/null.rb

@@ -0,0 +1,34 @@
+require 'sass/script/literal'
+
+module Sass::Script
+  # A SassScript object representing a null value.
+  class Null < Literal
+    # Creates a new null literal.
+    def initialize
+      super nil
+    end
+
+    # @return [Boolean] `false` (the Ruby boolean value)
+    def to_bool
+      false
+    end
+
+    # @return [Boolean] `true`
+    def null?
+      true
+    end
+
+    # @return [String] '' (An empty string)
+    def to_s(opts = {})
+      ''
+    end
+    alias_method :to_sass, :to_s
+
+    # Returns a string representing a null value.
+    #
+    # @return [String]
+    def inspect
+      'null'
+    end
+  end
+end

lib/sass/script/operation.rb

@@ -82,6 +82,11 @@ def _perform(environment)
 
       literal2 = @operand2.perform(environment)
 
+      literal_types = [literal1.class, literal2.class]
+      if !literal_types.include?(String) && literal_types.include?(Null)
+        raise Sass::SyntaxError.new("Invalid null operation: \"#{literal1.inspect} #{@operator} #{literal2.inspect}\".")
+      end
+
       begin
         opts(literal1.send(@operator, literal2))
       rescue NoMethodError => e

lib/sass/script/parser.rb

@@ -455,7 +455,7 @@ def number
       end
 
       def literal
-        (t = try_tok(:color, :bool)) && (return t.value)
+        (t = try_tok(:color, :bool, :null)) && (return t.value)
       end
 
       # It would be possible to have unified #assert and #try methods,

lib/sass/scss/rx.rb

@@ -130,7 +130,7 @@ def self.quote(str, flags = 0)
       # about 50 characters. This mitigates the problem of exponential parsing
       # time when a value has a long string of valid, parsable content followed
       # by something invalid.
-      STATIC_VALUE = /(-?#{NMSTART}|#{STRING_NOINTERP}|[ \t](?!%)|#[a-f0-9]|[,%]|#{NUM}|\!important){0,50}([;}])/i
+      STATIC_VALUE = /(-?#{NMSTART}|#{STRING_NOINTERP}|[ \t](?!%)|#[a-f0-9]|[,%]|#{NUM}|\!important){1,50}([;}])/i
       STATIC_SELECTOR = /(#{NMCHAR}|[ \t]|[,>+*]|[:#.]#{NMSTART}){0,50}([{])/i
     end
   end

lib/sass/tree/prop_node.rb

@@ -92,15 +92,19 @@ def declaration(opts = {:old => @prop_syntax == :old}, fmt = :sass)
       "#{initial}#{name}#{mid} #{self.class.val_to_sass(value, opts)}".rstrip
     end
 
+    # A property node is invisible if its value is empty.
+    #
+    # @return [Boolean]
+    def invisible?
+      resolved_value.empty?
+    end
+
     private
 
     def check!
       if @options[:property_syntax] && @options[:property_syntax] != @prop_syntax
         raise Sass::SyntaxError.new(
           "Illegal property syntax: can't use #{@prop_syntax} syntax when :property_syntax => #{@options[:property_syntax].inspect} is set.")
-      elsif resolved_value.empty?
-        raise Sass::SyntaxError.new("Invalid property: #{declaration.dump} (no value)." +
-          pseudo_class_selector_message)
       end
     end
 

lib/sass/tree/visitors/perform.rb

@@ -261,7 +261,8 @@ def visit_rule(node)
 
   # Loads the new variable value into the environment.
   def visit_variable(node)
-    return [] if node.guarded && !@environment.var(node.name).nil?
+    var = @environment.var(node.name)
+    return [] if node.guarded && var && !var.null?
     val = node.expr.perform(@environment)
     @environment.set_var(node.name, val)
     []

lib/sass/tree/visitors/to_css.rb

@@ -122,6 +122,7 @@ def visit_cssimport(node)
   end
 
   def visit_prop(node)
+    return if node.resolved_value.empty?
     tab_str = '  ' * (@tabs + node.tabs)
     if node.style == :compressed
       "#{tab_str}#{node.resolved_name}:#{node.resolved_value}"

test/sass/engine_test.rb

@@ -1011,7 +1011,7 @@ def test_debug_info
 
   def test_debug_info_without_filename
     assert_equal(<<CSS, Sass::Engine.new(<<SASS, :debug_info => true).render)
-@media -sass-debug-info{filename{font-family:}line{font-family:\\000031}}
+@media -sass-debug-info{filename{}line{font-family:\\000031}}
 foo {
   a: b; }
 CSS
@@ -1100,6 +1100,7 @@ def test_property_with_content_and_nested_props
   def test_guarded_assign
     assert_equal("foo {\n  a: b; }\n", render(%Q{$foo: b\n$foo: c !default\nfoo\n  a: $foo}))
     assert_equal("foo {\n  a: b; }\n", render(%Q{$foo: b !default\nfoo\n  a: $foo}))
+    assert_equal("foo {\n  a: b; }\n", render(%Q{$foo: null\n$foo: b !default\nfoo\n  a: $foo}))
   end
 
   def test_mixins
@@ -1185,6 +1186,35 @@ def test_default_values_for_mixin_arguments
   +foo(#fff, 2px)
 three
   +foo(#fff, 2px, 3px)
+SASS
+    assert_equal(<<CSS, render(<<SASS))
+one {
+  color: white;
+  padding: 1px;
+  margin: 4px; }
+
+two {
+  color: white;
+  padding: 2px;
+  margin: 5px; }
+
+three {
+  color: white;
+  padding: 2px;
+  margin: 3px; }
+CSS
+$a: 5px
+=foo($a, $b: 1px, $c: null)
+  $c: 3px + $b !default
+  color: $a
+  padding: $b
+  margin: $c
+one
+  +foo(#fff)
+two
+  +foo(#fff, 2px)
+three
+  +foo(#fff, 2px, 3px)
 SASS
   end
 
@@ -1393,6 +1423,15 @@ def test_complex_property_interpolation
   def test_if_directive
     assert_equal("a {\n  b: 1; }\n", render(<<SASS))
 $var: true
+a
+  @if $var
+    b: 1
+  @if not $var
+    b: 2
+SASS
+
+    assert_equal("a {\n  b: 2; }\n", render(<<SASS))
+$var: null
 a
   @if $var
     b: 1
@@ -1795,6 +1834,26 @@ def test_empty_selector_warning
 END
   end
 
+  def test_nonprinting_empty_property
+    assert_equal(<<CSS, render(<<SASS))
+a {
+  c: "";
+  e: f; }
+CSS
+$null-value: null
+$empty-string: ''
+$empty-list: (null)
+a
+  b: $null-value
+  c: $empty-string
+  d: $empty-list
+  e: f
+
+g
+  h: null
+SASS
+  end
+
   def test_root_level_pseudo_class_with_new_properties
     assert_equal(<<CSS, render(<<SASS, :property_syntax => :new))
 :focus {

test/sass/functions_test.rb

@@ -871,6 +871,7 @@ def test_type_of
     assert_equal("bool", evaluate("type-of(true)"))
     assert_equal("color", evaluate("type-of(#fff)"))
     assert_equal("color", evaluate("type-of($value: #fff)"))
+    assert_equal("null", evaluate("type-of(null)"))
   end
 
   def test_unit
@@ -1011,6 +1012,7 @@ def test_index
   def test_if
     assert_equal("1px", evaluate("if(true, 1px, 2px)"))
     assert_equal("2px", evaluate("if(false, 1px, 2px)"))
+    assert_equal("2px", evaluate("if(null, 1px, 2px)"))
   end
 
   def test_keyword_args_rgb