[Sass] Support @mixin and @include in the indented syntax.

doc-src/SASS_CHANGELOG.md

@@ -206,6 +206,28 @@ They behave identically to double-quoted strings,
 except that single quotes need to be backslash-escaped
 and double quotes do not.
 
+#### Mixin Definition and Inclusion
+
+Sass now supports the `@mixin` directive as a way of defining mixins (like `=`),
+as well as the `@include` directive as a way of including them (like `+`).
+The old syntax is *not* deprecated,
+and the two are fully compatible.
+For example:
+
+    @mixin pretty-text
+      color: $prettiest-color
+
+    a
+      @include pretty-text
+
+is the same as:
+
+    =pretty-text
+      color: $prettiest-color
+
+    a
+      +pretty-text
+
 ### Colors
 
 SassScript color values are much more powerful than they were before.

lib/sass/engine.rb

@@ -465,6 +465,10 @@ WARNING
         raise SyntaxError.new("Illegal nesting: Nothing may be nested beneath import directives.",
           :line => @line + 1) unless line.children.empty?
         value.split(/,\s*/).map {|f| Tree::ImportNode.new(f)}
+      elsif directive == "mixin"
+        parse_mixin_definition(line)
+      elsif directive == "include"
+        parse_mixin_include(line, root)
       elsif directive == "for"
         parse_for(line, root, value)
       elsif directive == "else"
@@ -528,7 +532,7 @@ WARNING
     end
 
     # @private
-    MIXIN_DEF_RE = /^=\s*(#{Sass::SCSS::RX::IDENT})(.*)$/
+    MIXIN_DEF_RE = /^(?:=|@mixin)\s*(#{Sass::SCSS::RX::IDENT})(.*)$/
     def parse_mixin_definition(line)
       name, arg_string = line.text.scan(MIXIN_DEF_RE).first
       raise SyntaxError.new("Invalid mixin \"#{line.text[1..-1]}\".") if name.nil?
@@ -541,7 +545,7 @@ WARNING
     end
 
     # @private
-    MIXIN_INCLUDE_RE = /^\+\s*(#{Sass::SCSS::RX::IDENT})(.*)$/
+    MIXIN_INCLUDE_RE = /^(?:\+|@include)\s*(#{Sass::SCSS::RX::IDENT})(.*)$/
     def parse_mixin_include(line, root)
       name, arg_string = line.text.scan(MIXIN_INCLUDE_RE).first
       raise SyntaxError.new("Invalid mixin include \"#{line.text}\".") if name.nil?

test/sass/engine_test.rb

@@ -834,6 +834,19 @@ SASS
     renders_correctly "mixins", { :style => :expanded }
   end
 
+  def test_directive_style_mixins
+    assert_equal <<CSS, render(<<SASS)
+bar {
+  prop: baz; }
+CSS
+@mixin foo($arg)
+  prop: $arg
+
+bar
+  @include foo(baz)
+SASS
+  end
+
   def test_mixins_dont_interfere_with_sibling_combinator
     assert_equal("foo + bar {\n  a: b; }\nfoo + baz {\n  c: d; }\n",
                  render("foo\n  +\n    bar\n      a: b\n    baz\n      c: d"))