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.

3 files changed, 51 insertions, 42 deletions

diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index 3595f60bf8..c2403c57a7 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -293,25 +293,25 @@ module Rails
       end
 
       private
-        def credentials_available_for_current_env?
-          File.exist?("#{root}/config/credentials/#{Rails.env}.yml.enc")
-        end
-
         def default_credentials_content_path
           if credentials_available_for_current_env?
-            File.join(root, "config", "credentials", "#{Rails.env}.yml.enc")
+            root.join("config", "credentials", "#{Rails.env}.yml.enc")
           else
-            File.join(root, "config", "credentials.yml.enc")
+            root.join("config", "credentials.yml.enc")
           end
         end
 
         def default_credentials_key_path
           if credentials_available_for_current_env?
-            File.join(root, "config", "credentials", "#{Rails.env}.key")
+            root.join("config", "credentials", "#{Rails.env}.key")
           else
-            File.join(root, "config", "master.key")
+            root.join("config", "master.key")
           end
         end
+
+        def credentials_available_for_current_env?
+          File.exist?(root.join("config", "credentials", "#{Rails.env}.yml.enc"))
+        end
     end
   end
 end
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`.
diff --git a/railties/lib/rails/commands/credentials/credentials_command.rb b/railties/lib/rails/commands/credentials/credentials_command.rb
index 4b30d208e0..852cd401d7 100644
--- a/railties/lib/rails/commands/credentials/credentials_command.rb
+++ b/railties/lib/rails/commands/credentials/credentials_command.rb
@@ -24,13 +24,11 @@ module Rails
 
         ensure_editor_available(command: "bin/rails credentials:edit") || (return)
 
-        encrypted = Rails.application.encrypted(content_path, key_path: key_path)
-
-        ensure_encryption_key_has_been_added(key_path) if encrypted.key.nil?
-        ensure_encrypted_file_has_been_added(content_path, key_path)
+        ensure_encryption_key_has_been_added if credentials.key.nil?
+        ensure_credentials_have_been_added
 
         catch_editing_exceptions do
-          change_encrypted_file_in_system_editor(content_path, key_path)
+          change_credentials_in_system_editor
         end
 
         say "File encrypted and saved."
@@ -41,36 +39,46 @@ module Rails
       def show
         require_application_and_environment!
 
-        encrypted = Rails.application.encrypted(content_path, key_path: key_path)
-
-        say encrypted.read.presence || missing_encrypted_message(key: encrypted.key, key_path: key_path, file_path: content_path)
+        say credentials.read.presence || missing_credentials_message
       end
 
       private
-        def content_path
-          options[:environment] ? "config/credentials/#{options[:environment]}.yml.enc" : "config/credentials.yml.enc"
-        end
-
-        def key_path
-          options[:environment] ? "config/credentials/#{options[:environment]}.key" : "config/master.key"
+        def credentials
+          Rails.application.encrypted(content_path, key_path: key_path)
         end
 
-
-        def ensure_encryption_key_has_been_added(key_path)
+        def ensure_encryption_key_has_been_added
           encryption_key_file_generator.add_key_file(key_path)
           encryption_key_file_generator.ignore_key_file(key_path)
         end
 
-        def ensure_encrypted_file_has_been_added(file_path, key_path)
-          encrypted_file_generator.add_encrypted_file_silently(file_path, key_path)
+        def ensure_credentials_have_been_added
+          encrypted_file_generator.add_encrypted_file_silently(content_path, key_path)
         end
 
-        def change_encrypted_file_in_system_editor(file_path, key_path)
-          Rails.application.encrypted(file_path, key_path: key_path).change do |tmp_path|
+        def change_credentials_in_system_editor
+          credentials.change do |tmp_path|
             system("#{ENV["EDITOR"]} #{tmp_path}")
           end
         end
 
+        def missing_credentials_message
+          if credentials.key.nil?
+            "Missing '#{key_path}' to decrypt credentials. See `rails credentials:help`"
+          else
+            "File '#{content_path}' does not exist. Use `rails credentials:edit` to change that."
+          end
+        end
+
+
+        def content_path
+          options[:environment] ? "config/credentials/#{options[:environment]}.yml.enc" : "config/credentials.yml.enc"
+        end
+
+        def key_path
+          options[:environment] ? "config/credentials/#{options[:environment]}.key" : "config/master.key"
+        end
+
 
         def encryption_key_file_generator
           require "rails/generators"
@@ -85,14 +93,6 @@ module Rails
 
           Rails::Generators::EncryptedFileGenerator.new
         end
-
-        def missing_encrypted_message(key:, key_path:, file_path:)
-          if key.nil?
-            "Missing '#{key_path}' to decrypt credentials. See `rails credentials:help`"
-          else
-            "File '#{file_path}' does not exist. Use `rails credentials:edit` to change that."
-          end
-        end
     end
   end
 end