Fix str.zfill() width calculation for non-ASCII strings (#7534)

crates/vm/src/anystr.rs

@@ -396,6 +396,10 @@ pub trait AnyStr {
 
     fn py_zfill(&self, width: isize) -> Vec<u8> {
         let width = width.to_usize().unwrap_or(0);
+        let char_len = self.elements().count();
+        let width = self
+            .bytes_len()
+            .saturating_add(width.saturating_sub(char_len));
         rustpython_common::str::zfill(self.as_bytes(), width)
     }
 

extra_tests/snippets/builtin_str.py

@@ -61,6 +61,9 @@ assert a.endswith(("A", "lo"))
 assert not a.endswith("on")
 assert not a.endswith(("A", "ll"))
 assert a.zfill(8) == "000Hallo"
+assert "á".zfill(4) == "000á"
+assert "🙂".zfill(5) == "0000🙂"
+assert "+あ".zfill(5) == "+000あ"
 assert a.isalnum()
 assert not a.isdigit()
 assert not a.isdecimal()