Add comment skipping to lexer

* Comment and whitespace skipping is now handed by a regex
* Remove skip_whitespace and adv_char since they aren't used anymore
* Fix pos_text() to return a reference with the correct lifetime
* Add comment skipping tests

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/lexer.rs

@@ -37,7 +37,7 @@ impl<'t> Lexer<'t> {
         self.pos_text().chars()
     }
 
-    fn pos_text(&self) -> &str {
+    fn pos_text(&self) -> &'t str {
         &self.text[self.pos.byte..]
     }
 
@@ -45,22 +45,6 @@ impl<'t> Lexer<'t> {
         self.chars().next()
     }
 
-    fn skip_whitespace(&mut self) {
-        while let Some(c) = self.curr_char() {
-            if !c.is_whitespace() || c == '\n' {
-                break;
-            } else {
-                self.adv_char();
-            }
-        }
-    }
-
-    fn adv_char(&mut self) -> Option<char> {
-        let c = self.curr_char()?;
-        self.pos = self.pos.next_char(c);
-        Some(c)
-    }
-
     ////////////////////////////////////////////////////////////////////////////////
     // Tokens
     ////////////////////////////////////////////////////////////////////////////////
@@ -107,6 +91,10 @@ impl<'t> Lexer<'t> {
             .ignore_whitespace(true)
             .build()
             .unwrap();
+
+            static ref SKIP_REGEX: Regex = Regex::new(
+                r"^((#[^\n]*)\n?|[ \t\r]+)+"
+            ).unwrap();
         }
 
         const CAPTURES: &[(&str, TokenKind)] = &[
@@ -143,7 +131,9 @@ impl<'t> Lexer<'t> {
             ("newline", TokenKind::Newline),
         ];
 
-        self.skip_whitespace();
+        if let Some(skip) = SKIP_REGEX.find(self.pos_text()) {
+            self.pos.adv_str(skip.as_str());
+        }
 
         if self.curr_char().is_none() {
             return Ok(None);
@@ -151,7 +141,7 @@ impl<'t> Lexer<'t> {
 
         let caps =
             REGEX
-                .captures(&self.text[self.pos.byte..])
+                .captures(self.pos_text())
                 .ok_or_else(|| Error::Unexpected {
                     what: "EOF".to_string(),
                     pos: self.pos,
@@ -219,6 +209,11 @@ mod test {
         let mut lexer = Lexer::new("   \t \r \r\r\t\t    ");
         assert!(matches!(lexer.next_token(), Ok(None)));
         assert!(lexer.is_eof());
+
+        let mut lexer = Lexer::new(r"#comment
+            #another comment");
+        assert!(matches!(lexer.next_token(), Ok(None)));
+        assert!(lexer.is_eof());
     }
 
     #[test]