Fix a Python bug: when package is empty, DescriptorDatabase FindFileC…

…ontainingSymbol method will able to find symbol names not start with '.'

The old behavior requires a prefix of '.' for empty packages like '.Foo'. To not break old behaviors, both 'Foo' and '.Foo' will be supported. The support for leading '.' will be removed around 2026 Jan.

For example:
db.FindFileContainingSymbol('Foo')
db.FindFileContainingSymbol('.Foo') # with a warning
will have same result

PiperOrigin-RevId: 695493356

python/google/protobuf/descriptor_database.py

@@ -52,14 +52,24 @@ def Add(self, file_desc_proto):
       for name in _ExtractSymbols(message, package):
         self._AddSymbol(name, file_desc_proto)
     for enum in file_desc_proto.enum_type:
-      self._AddSymbol(('.'.join((package, enum.name))), file_desc_proto)
+      self._AddSymbol(
+          ('.'.join((package, enum.name)) if package else enum.name),
+          file_desc_proto,
+      )
       for enum_value in enum.value:
         self._file_desc_protos_by_symbol[
-            '.'.join((package, enum_value.name))] = file_desc_proto
+            '.'.join((package, enum_value.name)) if package else enum_value.name
+        ] = file_desc_proto
     for extension in file_desc_proto.extension:
-      self._AddSymbol(('.'.join((package, extension.name))), file_desc_proto)
+      self._AddSymbol(
+          ('.'.join((package, extension.name)) if package else extension.name),
+          file_desc_proto,
+      )
     for service in file_desc_proto.service:
-      self._AddSymbol(('.'.join((package, service.name))), file_desc_proto)
+      self._AddSymbol(
+          ('.'.join((package, service.name)) if package else service.name),
+          file_desc_proto,
+      )
 
   def FindFileByName(self, name):
     """Finds the file descriptor proto by file name.
@@ -102,6 +112,14 @@ def FindFileContainingSymbol(self, symbol):
     Raises:
       KeyError if no file contains the specified symbol.
     """
+    if symbol.count('.') == 1 and symbol[0] == '.':
+      symbol = symbol.lstrip('.')
+      warnings.warn(
+          'Please remove the leading "." when '
+          'FindFileContainingSymbol, this will turn to error '
+          'in 2026 Jan.',
+          RuntimeWarning,
+      )
     try:
       return self._file_desc_protos_by_symbol[symbol]
     except KeyError:

python/google/protobuf/internal/descriptor_database_test.py

@@ -56,8 +56,26 @@ def testAdd(self):
         'google.protobuf.python.internal.Factory2Enum.FACTORY_2_VALUE_0'))
     self.assertEqual(file_desc_proto, db.FindFileContainingSymbol(
         'google.protobuf.python.internal.FACTORY_2_VALUE_0'))
-    self.assertEqual(file_desc_proto2, db.FindFileContainingSymbol(
-        '.NO_PACKAGE_VALUE_0'))
+    self.assertEqual(
+        file_desc_proto2, db.FindFileContainingSymbol('NO_PACKAGE_VALUE_0')
+    )
+    self.assertEqual(
+        file_desc_proto2, db.FindFileContainingSymbol('.NO_PACKAGE_VALUE_0')
+    )
+    self.assertEqual(
+        file_desc_proto2, db.FindFileContainingSymbol('NoPackageMessage')
+    )
+    self.assertEqual(
+        file_desc_proto2, db.FindFileContainingSymbol('.NoPackageMessage')
+    )
+    self.assertEqual(
+        file_desc_proto2,
+        db.FindFileContainingSymbol('NoPackageEnum'),
+    )
+    self.assertEqual(
+        file_desc_proto2,
+        db.FindFileContainingSymbol('.NoPackageEnum'),
+    )
     # Can find top level extension.
     self.assertEqual(file_desc_proto, db.FindFileContainingSymbol(
         'google.protobuf.python.internal.another_field'))
@@ -80,6 +98,11 @@ def testAdd(self):
     with self.assertRaisesRegex(KeyError, r'\'protobuf_unittest\.NoneMessage\''):
       db.FindFileContainingSymbol('protobuf_unittest.NoneMessage')
 
+    with self.assertRaises(KeyError):
+      db.FindFileContainingSymbol(
+          '.google.protobuf.python.internal.FACTORY_2_VALUE_0'
+      )
+
   def testConflictRegister(self):
     db = descriptor_database.DescriptorDatabase()
     unittest_fd = descriptor_pb2.FileDescriptorProto.FromString(