Config.import_config

You're seeing just the macro import_config, go back to Config module for more information.
Link to this macro

import_config(file)

View Source (macro) (since 1.9.0)

Imports configuration from the given file.

In case the file doesn't exist, an error is raised.

If file is a relative, it will be expanded relatively to the directory the current configuration file is in.

Examples

This is often used to emulate configuration across environments:

import_config "#{config_env()}.exs"

Note, however, some configuration files, such as config/runtime.exs does not support imports, as they are meant to be copied across systems.