lex: fix single 0 recognition

src/lex/mod.rs

@@ -277,8 +277,13 @@ impl Lexer {
             Some('x') => self.read_int_literal(16),
             Some('o') => self.read_int_literal(8),
             Some('b') => self.read_int_literal(2),
-            Some(c) => self.syntax_error(format!("Unexpected character '{}'", c)),
-            None => self.syntax_error(String::from("Unexpected end-of-file")),
+            Some(c @ '0'..='9') => self.syntax_error(String::from("Decimal literals must not start with a 0")),
+            Some(c) if c.is_ident_part() => self.syntax_error(format!("Unexpected character '{}'", c)),
+            _ => {
+                // it wasn't a prefixed int literal at all, just a single 0
+                self.cursor.prev();
+                self.token_ok(token::Kind::IntLiteral)
+            },
         }
     }