Merge pull request #886 from Mange/negative-nth

Add support for an-b in nth selectors

lib/nokogiri/css/parser.y

@@ -130,7 +130,7 @@ rule
     | FUNCTION expr RPAREN {
         result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
       }
-    | FUNCTION an_plus_b RPAREN {
+    | FUNCTION nth RPAREN {
         result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
       }
     | NOT expr RPAREN {
@@ -150,10 +150,10 @@ rule
       {
         if val[0] == 'even'
           val = ["2","n","+","0"]
-          result = Node.new(:AN_PLUS_B, val)
+          result = Node.new(:NTH, val)
         elsif val[0] == 'odd'
           val = ["2","n","+","1"]
-          result = Node.new(:AN_PLUS_B, val)
+          result = Node.new(:NTH, val)
         else
           # This is not CSS standard.  It allows us to support this:
           # assert_xpath("//a[foo(., @href)]", @parser.parse('a:foo(@href)'))
@@ -163,33 +163,39 @@ rule
         end
       }
     ;
-  an_plus_b
+  nth
     : NUMBER IDENT PLUS NUMBER          # 5n+3 -5n+3
       {
         if val[1] == 'n'
-          result = Node.new(:AN_PLUS_B, val)
+          result = Node.new(:NTH, val)
         else
           raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
         end
       }
     | IDENT PLUS NUMBER {               # n+3, -n+3
         if val[0] == 'n'
           val.unshift("1")
-          result = Node.new(:AN_PLUS_B, val)
+          result = Node.new(:NTH, val)
         elsif val[0] == '-n'
           val[0] = 'n'
           val.unshift("-1")
-          result = Node.new(:AN_PLUS_B, val)
+          result = Node.new(:NTH, val)
         else
           raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
         end
       }
-    | NUMBER IDENT                      # 5n, -5n
-      {
-        if val[1] == 'n'
+    | NUMBER IDENT {                    # 5n, -5n, 10n-1
+        n = val[1]
+        if n[0, 2] == 'n-'
+          val[1] = 'n'
+          val << "-"
+          # b is contained in n as n is the string "n-b"
+          val << n[2, n.size]
+          result = Node.new(:NTH, val)
+        elsif n == 'n'
           val << "+"
           val << "0"
-          result = Node.new(:AN_PLUS_B, val)
+          result = Node.new(:NTH, val)
         else
           raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
         end

lib/nokogiri/css/xpath_visitor.rb

@@ -14,14 +14,14 @@ def visit_function node
         when /^eq\(/
           "position() = #{node.value[1]}"
         when /^(nth|nth-of-type|nth-child)\(/
-          if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :AN_PLUS_B
-            an_plus_b(node.value[1])
+          if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :NTH
+            nth(node.value[1])
           else
             "position() = #{node.value[1]}"
           end
         when /^(nth-last-child|nth-last-of-type)\(/
-          if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :AN_PLUS_B
-            an_plus_b(node.value[1], :last => true)
+          if node.value[1].is_a?(Nokogiri::CSS::Node) and node.value[1].type == :NTH
+            nth(node.value[1], :last => true)
           else
             index = node.value[1].to_i - 1
             index == 0 ? "position() = last()" : "position() = last() - #{index}"
@@ -151,11 +151,10 @@ def accept node
       end
 
     private
-      def an_plus_b node, options={}
+      def nth node, options={}
         raise ArgumentError, "expected an+b node to contain 4 tokens, but is #{node.value.inspect}" unless node.value.size == 4
 
-        a = node.value[0].to_i
-        b = node.value[3].to_i
+        a, b = read_a_and_positive_b node.value
         position = options[:last] ? "(last()-position()+1)" : "position()"
 
         if (b == 0)
@@ -166,6 +165,19 @@ def an_plus_b node, options={}
         end
       end
 
+      def read_a_and_positive_b values
+        op = values[2]
+        if op == "+"
+          a = values[0].to_i
+          b = values[3].to_i
+        elsif op == "-"
+          a = values[0].to_i
+          b = a - (values[3].to_i % a)
+        else
+          raise ArgumentError, "expected an+b node to have either + or - as the operator, but is #{op.inspect}"
+        end
+        [a, b]
+      end
     end
   end
 end

test/css/test_nthiness.rb

@@ -74,6 +74,10 @@ def test_mnp3
         assert_result_rows [1,2,3], @parser.search("table/tr:nth(-n+3)")
       end
 
+      def test_4nm1
+        assert_result_rows [3,7,11], @parser.search("table/tr:nth(4n-1)")
+      end
+
       def test_np3
         assert_result_rows [3,4,5,6,7,8,9,10,11,12,13,14], @parser.search("table/tr:nth(n+3)")
       end

test/css/test_tokenizer.rb

@@ -152,7 +152,7 @@ def test_scan_function_selector
         ], @scanner)
       end
 
-      def test_scan_an_plus_b
+      def test_scan_nth
         @scanner.scan('x:nth-child(5n+3)')
         assert_tokens([ [:IDENT, 'x'],
                         [':', ':'],