Add a "subsequence?" helper to Util.

lib/sass/util.rb

@@ -253,6 +253,23 @@ def check_range(name, range, value, unit='')
         "#{name} #{str} must be between #{range.first}#{unit} and #{range.last}#{unit}")
     end
 
+    # Returns whether or not `seq1` is a subsequence of `seq2`. That is, whether
+    # or not `seq2` contains every element in `seq1` in the same order (and
+    # possibly more elements besides).
+    #
+    # @param seq1 [Array]
+    # @param seq2 [Array]
+    # @return [Boolean]
+    def subsequence?(seq1, seq2)
+      i = j = 0
+      loop do
+        return true if i == seq1.size
+        return false if j == seq2.size
+        i += 1 if seq1[i] == seq2[j]
+        j += 1
+      end
+    end
+
     # Returns information about the caller of the previous method.
     #
     # @param entry [String] An entry in the `#caller` list, or a similarly formatted string

test/sass/util_test.rb

@@ -120,6 +120,16 @@ def test_lcs_with_block
       lcs([-5, 3, 2, 8], [-4, 1, 8]) {|a, b| (a - b).abs <= 1 && [a, b].max})
   end
 
+  def test_subsequence
+    assert(subsequence?([1, 2, 3], [1, 2, 3]))
+    assert(subsequence?([1, 2, 3], [1, :a, 2, :b, 3]))
+    assert(subsequence?([1, 2, 3], [:a, 1, :b, :c, 2, :d, 3, :e, :f]))
+
+    assert(!subsequence?([1, 2, 3], [1, 2]))
+    assert(!subsequence?([1, 2, 3], [1, 3, 2]))
+    assert(!subsequence?([1, 2, 3], [3, 2, 1]))
+  end
+
   def test_silence_warnings
     old_stderr, $stderr = $stderr, StringIO.new
     warn "Out"