Is organizing config files within a config group in a directory structure a supported feature in hydra?

Question

Let's assume a config group foo and config files organized in the following directory structure:

conf
├── foo
│   ├── bar
│   │   ├── a.yaml
│   │   ├── b.yaml
│   │   ├── c.yaml
│   └── baz
│       ├── d.yaml
│       ├── e.yaml
│       └── f.yaml

Each of the yaml files sets the package to foo using # @package foo. When running the corresponding application, I can simply override foo by specifying something like foo=bar/a or foo=baz/f. Thereby, the sub-directories bar and baz indicate a certain category withing a larger set of possible configurations.

While this works fine for standard use in hydra, some more advanced features of hydra appear to be not compatible with this structure. For instance, I would like to use glob in conjunction with the directory structure like this foo=glob(bar/*) to sweep over all configs of a certain category. However, this does not appear to work as glob does not find any configs in this example. Also if I assign an invalid config to foo and hydra lists the available options, the list is empty.

This makes me wonder if structuring within a config group is a generally supported feature in hydra, and just some corner cases are not covered yet, or if I am using hydra wrong and directories should not be used for organizing configs in a group?

Answer 1

This is not recommended, but not explicitly prohibited. There are scenarios where this can help, but as you have discovered it does not play well with some other features. A config group contains other config groups/configs.

Hydra 1.1 is adding support for recursive default lists which will make this kind of scenario more common. See The Defaults List documentation page:

├── server
│   ├── db
│   │   ├── mysql.yaml
│   │   └── sqlite.yaml
│   └── apache.yaml
└── config.yaml

In the scenario from the example there, the entities under server/db are different than the entities under server, so such globing would not make sense.