[Sass] Add a sass function unitless() that returns a boolean indicating if a number is unitless.

doc-src/SASS_CHANGELOG.md

@@ -13,6 +13,7 @@ of obsolete APIs.
 
 * `type-of` -- Returns the type of a value.
 * `unit` -- Returns the units associated with a number.
+* `unitless` -- Returns whether a number has units or not.
 
 ### `@warn`
 

lib/sass/script/functions.rb

@@ -113,6 +113,9 @@ module Sass::Script
   # \{#unit}
   # : Returns the units associated with a number.
   #
+  # \{#unitless}
+  # : Returns whether a number has units or not.
+  #
   # These functions are described in more detail below.
   #
   # ## Adding Custom Functions
@@ -711,6 +714,20 @@ module Sass::Script
       Sass::Script::String.new(number.unit_str, :string)
     end
 
+    # Inspects the unit of the number, returning a boolean indicating if it is unitless.
+    # For example:
+    #
+    #     unitless(100) => true
+    #     unitless(100px) => false
+    #
+    # @param number [Literal] The number to inspect
+    # @return [Bool] indicating if the number is unitless
+    # @raise [ArgumentError] if `number` isn't a number
+    def unitless(number)
+      assert_type number, :Number
+      Sass::Script::Bool.new(number.unitless?)
+    end
+
     # Converts a decimal number to a percentage.
     # For example:
     #

test/sass/functions_test.rb

@@ -522,6 +522,12 @@ MSG
     assert_error_message("#ff0000 is not a number for `unit'", "unit(#f00)")
   end
 
+  def test_unitless
+    assert_equal(%Q{true}, evaluate("unitless(100)"))
+    assert_equal(%Q{false}, evaluate("unitless(100px)"))
+    assert_error_message("#ff0000 is not a number for `unitless'", "unitless(#f00)")
+  end
+
   private
 
   def evaluate(value)