[Feature Request] support use case of composing the same config node in multiple places in the config tree

🚀 Feature Request

Be able to copy all the elements of one config in an other.

Motivation

In my code I have 2 modules which are trained, meaning that I have 2 optimizers. I would like to modify the parameters of one optimizer, but don’t want to copy have all default optimizer values written twice. I.e would like to do that python main.py module1.optimizer=adam module1.optimizer.lr=0.01 module2.optimizer.lr=0.01 but not have to define a optimize twice. Something like that:

module1:
  ...
  optimizer: ${optimizer.adam}

module2:
  ...
  optimizer: ${optimizer.adam}

which would use the adam optimizer as default for module 1 and 2 without having to dupicate it.

[omry]

Another idea to play with:

group@path=name

or in defaults:

defaults:
  - db@src_db: mysql
  - db@dst_db: mysql

I kind of like this one.

[omry]

until this is implemented, a workaround can be implemented as a symlink at the file system level: optimizer1/{adam,nexterov,sgd>.yaml optimizer2 -> optimizer1