Handle an invalid plural index in msgstr[...] instead of raising ValueError

read_po parsed the plural index of a `msgstr[N]` line with `int(idxarg[:-1])`,
which leaked a bare `ValueError: invalid literal for int()` to the caller when N
was not an integer (e.g. `msgstr[\x0c]`).

Route a non-integer index through the parser's existing `_invalid_pofile`
handling, so it raises a `PoFileError` when `abort_invalid=True` and otherwise
warns and skips the line, consistent with other malformed input.

Fixes #1209

Author: vineethsaivs

babel/messages/pofile.py

@@ -276,7 +276,11 @@ def _process_keyword_line(self, lineno, line, obsolete=False) -> None:
             self.in_msgid = False
             self.in_msgstr = True
             kwarg, has_bracket, idxarg = keyword.partition('[')
-            idx = int(idxarg[:-1]) if has_bracket else 0
+            try:
+                idx = int(idxarg[:-1]) if has_bracket else 0
+            except ValueError:
+                self._invalid_pofile(line, lineno, f"Invalid plural index in keyword {keyword!r}")
+                return
             s = _NormalizedString(arg) if arg != '""' else _NormalizedString()
             self.translations.append([idx, s])
             return

tests/messages/test_pofile.py

@@ -160,3 +160,17 @@ def test_issue_1134(case: str, abort_invalid: bool):
         output = pofile.read_po(buf)
         assert len(output) == 1
         assert output["foo"].string in ((''), ('', ''))
+
+
+@pytest.mark.parametrize("abort_invalid", [False, True])
+def test_invalid_msgstr_index_issue_1209(abort_invalid: bool):
+    # Regression test for #1209: a non-integer plural index in msgstr[...] must be reported
+    # through the normal invalid-pofile handling, not leak a bare ValueError from int().
+    buf = StringIO('msgstr[\x0c]')
+
+    if abort_invalid:
+        with pytest.raises(pofile.PoFileError):
+            pofile.read_po(buf, abort_invalid=True)
+    else:
+        # No crash: an invalid entry is skipped with a warning.
+        pofile.read_po(buf)