Restructure credentials after environment overrides.

Follow up to: e0d3313

- Revert renames from `encrypted` and `encrypted_file` back to `credentials`.
  They might be using our Encrypted* generators but from that level of abstraction
  they're still about credentials.

- Same vein: extract a `credentials` method for the `encrypted` local variable. But
  don't call it `encrypted` just because it uses that under the hood. It's about
  capturing the credentials. It's also useful in `change_credentials_in_system_editor`.

- Remove lots of needless argument passing. We've abstracted content_path and key_path
  into methods for a reason, so they should be used. Also spares a conspicuous rename
  of content_path into file_path in other methods.

- Reorders private methods so they're grouped into: command building blocks, option
  parsers, and the generators.

- Extracts commonality in the credentials application tests. A tad unsure about this.
  But I do like that we go with key, content thus matching the command and remove the
  yield which isn't really needed.

- Moves test/credentials_test.rb to beneath the test/application directory. It's a
  Rails application test, so it should be in there.

- Uses `root.join` — a neat trick gleaned from the tests! — and composes the configuration
  private methods such that the building block is below the callers.

1 files changed, 15 insertions, 6 deletions

diff --git a/railties/lib/rails/commands/credentials/USAGE b/railties/lib/rails/commands/credentials/USAGE
index 6b33d1ab74..d235592f46 100644
--- a/railties/lib/rails/commands/credentials/USAGE
+++ b/railties/lib/rails/commands/credentials/USAGE
@@ -41,9 +41,18 @@ from leaking.
 
 === Environment Specific Credentials
 
-It is possible to have credentials for each environment. If the file for current environment exists it will take
-precedence over `config/credentials.yml.enc`, thus for `production` environment first look for
-`config/credentials/production.yml.enc` that can be decrypted using master key taken from `ENV["RAILS_MASTER_KEY"]`
-or stored in `config/credentials/production.key`.
-To edit given file use command `rails credentials:edit --environment production`
-Default paths can be overwritten by setting `config.credentials.content_path` and `config.credentials.key_path`.
+The `credentials` command supports passing an `--environment` option to create an
+environment specific override. That override will takes precedence over the
+global `config/credentials.yml.enc` file when running in that environment. So:
+
+   rails credentials:edit --environment development
+
+will create `config/credentials/development.yml.enc` with the corresponding
+encryption key in `config/credentials/development.key` if the credentials file
+doesn't exist.
+
+The encryption key can also be put in `ENV["RAILS_MASTER_KEY"]`, which takes
+precedence over the file encryption key.
+
+In addition to that, the default credentials lookup paths can be overriden through
+`config.credentials.content_path` and `config.credentials.key_path`.