Parse nth-child(-/*comment*/n+b) (fixes servo#153)

Author: Manishearth

src/css-parsing-tests/An+B.json

@@ -80,6 +80,8 @@
 " -n +1", [-1, 1],
 "+ n +1", null,
 "- N +1", null,
+"+/**/n +1", [1, 1],
+"-/**/N +1", [-1, 1],
 
 "3N -1", [3, -1],
 "+2n -1 ", [2, -1],

src/nth.rs

@@ -12,7 +12,8 @@ use super::{Token, Parser};
 /// in which case the caller needs to check if the arguments’ parser is exhausted.
 /// Return `Ok((A, B))`, or `Err(())` for a syntax error.
 pub fn parse_nth(input: &mut Parser) -> Result<(i32, i32), ()> {
-    match try!(input.next()) {
+    let tok = try!(input.next());
+    match tok {
         Token::Number(value) => Ok((0, try!(value.int_value.ok_or(())) as i32)),
         Token::Dimension(value, unit) => {
             let a = try!(value.int_value.ok_or(())) as i32;
@@ -37,12 +38,17 @@ pub fn parse_nth(input: &mut Parser) -> Result<(i32, i32), ()> {
                 }
             }
         }
-        Token::Delim('+') => match try!(input.next_including_whitespace()) {
-            Token::Ident(value) => {
-                match_ignore_ascii_case! { &value,
-                    "n" => parse_b(input, 1),
-                    "n-" => parse_signless_b(input, 1, -1),
-                    _ => Ok((1, try!(parse_n_dash_digits(&*value))))
+        Token::Delim('+')| Token::Delim('-') => match try!(input.next_including_whitespace()) {
+            Token::Ident(n) => {
+                let val = if Token::Delim('+') == tok {
+                    1
+                } else {
+                    -1
+                };
+                match_ignore_ascii_case! { &n,
+                    "n" => parse_b(input, val),
+                    "n-" => parse_signless_b(input, val, -1),
+                    _ => Ok((1, try!(parse_n_dash_digits(&*n))))
                 }
             }
             _ => Err(())