lex: fix yet another token position bug

When skipping whitespace, the token position must
be updated accordingly.  Additionally, the token
position is now updated when creating a new one.
It still doesn't work because something with the
cursor is broken.

src/lex/mod.rs

@@ -52,6 +52,8 @@ impl Iterator for Lexer {
             c if c.is_ascii_whitespace() => {
                 self.cursor.skip_whitespace();
                 self.cursor.chop();
+                self.token_line = self.cursor.line();
+                self.token_col = self.cursor.col();
                 self.next()?
             }
             ',' => self.token_ok(token::Kind::Comma),
@@ -114,9 +116,6 @@ impl Iterator for Lexer {
             c => self.syntax_error(format!("Unexpected character '{}'", c)),
         };
 
-        if let Ok(token) = &result {
-            self.history.push(token.clone());
-        }
         Some(result)
     }
 }
@@ -148,9 +147,13 @@ impl Lexer {
     }
 
     pub fn prev(&mut self) -> Option<&Token> {
-        self.offset += 1;
-        let prev = &self.history[self.history.len() - self.offset];
-        Some(prev)
+        if self.offset < self.history.len() - 1 {
+            self.offset += 1;
+            let prev = &self.history[self.history.len() - self.offset];
+            Some(prev)
+        } else {
+            None
+        }
     }
 
     pub fn expect_kind(&mut self, kind: token::Kind) -> Result<Token, Error> {
@@ -261,6 +264,7 @@ impl Lexer {
         };
         self.token_line = self.cursor.line();
         self.token_col = self.cursor.col();
+        self.history.push(t.clone());
         t
     }