fix(issue #1219): Exception raised if the revision date is blank

.gitignore

@@ -23,3 +23,6 @@ tests/messages/data/project/i18n/en_US
 tests/messages/data/project/i18n/fi_BUGGY/LC_MESSAGES/*.mo
 tests/messages/data/project/i18n/long_messages.pot
 tests/messages/data/project/i18n/temp*
+.cie/
+.venv/
+.forge/

babel/messages/catalog.py

@@ -103,8 +103,12 @@ def _has_python_brace_format(string: str) -> bool:
     return field_name_seen
 
 
-def _parse_datetime_header(value: str) -> datetime.datetime:
+def _parse_datetime_header(value: str) -> datetime.datetime | None:
     match = re.match(r'^(?P<datetime>.*?)(?P<tzoffset>[+-]\d{4})?$', value)
+    if not match.group('datetime'):
+        # Some tools (e.g. Poedit) emit a blank date header instead of
+        # eliding it altogether; leave the date unset in that case.
+        return None
 
     dt = datetime.datetime.strptime(match.group('datetime'), '%Y-%m-%d %H:%M')
 

tests/test_forge_1219.py

@@ -0,0 +1,34 @@
+"""Regression test for blank PO-Revision-Date header.
+
+When a .po file has a blank PO-Revision-Date field (as produced by some
+tools like Poedit), pybabel raises a ValueError from
+``_parse_datetime_header`` because it tries to parse an empty string.
+The revision date should simply be left unset in that case.
+"""
+
+import pytest
+
+from babel.messages.catalog import Catalog
+
+
+def test_blank_po_revision_date_does_not_raise():
+    """A blank PO-Revision-Date should not raise an exception."""
+    catalog = Catalog()
+    # Simulate the headers that a .po file with a blank PO-Revision-Date
+    # would contain.
+    headers = [
+        ("PO-Revision-Date", ""),
+    ]
+    # This should not raise; revision_date should remain None.
+    catalog._set_mime_headers(headers)
+    assert catalog.revision_date is None
+
+
+def test_blank_pot_creation_date_does_not_raise():
+    """A blank POT-Creation-Date should not raise an exception either."""
+    catalog = Catalog()
+    headers = [
+        ("POT-Creation-Date", ""),
+    ]
+    catalog._set_mime_headers(headers)
+    assert catalog.creation_date is None