Fix shared config feature in 3-tier config

[eileencodes]

Rails allows you to use a shared entry in the database yaml which gets
merged into other entries. This was broken when using a 3-tier config.

The change here ensures we're looping through all the configs. We know
we have a 3-tier config if the config is a hash and all the values
inside that config are a hash. If so we need to keep looping, otherwise
we have a standard 2-tier config.

Fixes #45299

[jasonkarns]

Is there an expectation that the shared entry would be able to support per-database options?

The original issue #45299 had a sample config where shared had distinct options for each database:

shared:
   foo:
     migrations_paths:
       - "db/foo"

   bar:
     migrations_paths:
       - "db/bar"

I'm running Rails 7.0.4 (which seems to have this patch included), and the current behavior merges shared into each database, rather than merged with each environment.

ie:

shared:
  pool: 15 # all dbs get same pool option

I'm not sure which one is preferred; there are pros and cons to each. The current implementation makes it easy to set defaults that would apply to all databases across all environments. However, it's not possible to set defaults unique per database across all environments.

[eileencodes]

and the current behavior merges shared into each database, rather than merged with each environment.

I'm not following the expected vs actual behavior you're asking about. If you think there is a bug please open a new issue with a reproduction.

However, I think the current implementation is correct. Since Rails creates database configuration objects from the info in the database.yml, there's no environment to access once they are created. We don't have a concept of a higher level of shared information that doesn't get merged directly into the database config object.

[jasonkarns]

Opened #47367 as related. Thanks!