For the read-from-stdin feature in pylint an AST is constructed using

AstroidBuilder(MANAGER).string_build(data, modname, filepath)

whereas for regular modules it is constructed using

MANAGER.ast_from_file(filepath, modname, source=True)

See the get_ast method in https://github.com/PyCQA/pylint/pull/3257/files/5b24700e7bf84d1f2ae6fcd468acf5a9f6f1c458

The module docstring of astroid.manager suggests that the Manager should be used for both cases in pylint.

Therefore, AstroidManager should provide a way to create an AST from a string.