Spread operator in const collection literals

The feature spec describes being able to write code like

const list = [2, 3];
const another = [1, ...list, 4]; // [1, 2, 3, 4].
main() => print(another);

However this fails to compile with the error:

$dart example/dart.dart
example/example.dart:4:21: Error: '...' is not supported in constant expressions.
const another = [1, ...list, 4]; // [1, 2, 3, 4].
                    ^^^

Version information:

• Dart VM version: 2.4.0 (Wed Jun 19 11:53:45 2019 +0200) on "windows_x64"
• IntelliJ IDEA 2019.2 (Ultimate Edition) Build #IU-192.5728.98

This annotation processor is my use case. I’d like to split the queries parameter into maps defined in different files. For example:

// In queries/todos.dart
const todoQueries = {
  'getTodos': 'SELECT * FROM todo'
};

// In database.dart
@UseMoor(
  queries: {
    'getUsers': 'SELECT * FROM user',
    ...todoQueries,
  },
)
class TodoDb extends _$TodoDb {

Interestingly, pub run build_runner build runs without issue and the annotation processor spreads the todoQueries as expected, even though the analyzer has underlined it: