forbit empty punycoded hostnames

Author: antonok-edm

src/content_blocking.rs

@@ -1365,6 +1365,8 @@ mod filterset_tests {
             "||insaattrendy.com/Upload/bükerbanner*.jpg",
             // from domain
             "/siropu/am/core.min.js$script,important,from=~audi-sport.net|~hifiwigwam.com",
+            // leading zero-width space
+            r#"​##a[href^="https://www.g2fame.com/"] > img"#,
         ], Default::default());
 
         let (cb_rules, used_rules) = set.into_content_blocking()?;

src/filters/cosmetic.rs

@@ -192,8 +192,8 @@ impl CosmeticFilter {
             } else {
                 *mask |= CosmeticFilterMask::IS_UNICODE;
                 match idna::domain_to_ascii(location) {
-                    Ok(x) => hostname.push_str(&x),
-                    Err(_) => return Err(CosmeticFilterError::PunycodeError),
+                    Ok(x) if !x.is_empty() => hostname.push_str(&x),
+                    _ => return Err(CosmeticFilterError::PunycodeError),
                 }
             }
             let hash = crate::utils::fast_hash(&hostname);
@@ -1982,6 +1982,11 @@ mod matching_tests {
         assert!(parse_cf("example.com###adBanner:remove-class(src)").is_ok());
     }
 
+    #[test]
+    fn zero_width_space() {
+        assert!(parse_cf(r#"​##a[href^="https://www.g2fame.com/"] > img"#).is_err());
+    }
+
     #[test]
     #[cfg(feature = "css-validation")]
     fn abp_has_conversion() {