docs: document config/ and some directories in app/.

* Add README files to several directories in app/ giving a brief
  overview of some parts of Danbooru's architecture.
* Add documentation for files in config/.

config/README.md

@@ -0,0 +1,14 @@
+# Config
+
+This directory contains configuration files for Danbooru.
+
+To configure your Danbooru instance, copy [danbooru_default_config.rb](./danbooru_default_config.rb)
+to [danbooru_local_config.rb](./danbooru_local_config.rb) and edit it. See
+[danbooru_default_config.rb](./danbooru_default_config.rb) for details.
+
+The only file here that end users need to be concerned about is [danbooru_default_config.rb](./danbooru_default_config.rb).
+The rest of the files here are internal Rails-related configuration files that end users shouldn't need to edit.
+
+# External links
+
+* https://guides.rubyonrails.org/configuring.html

config/application.rb

@@ -1,4 +1,10 @@
+# This file runs after config/boot.rb and before config/environment.rb. It loads Rails, loads the gems, loads the
+# Danbooru configuration, and does some basic Rails configuration.
+#
+# @see https://guides.rubyonrails.org/initialization.html
+
 require_relative 'boot'
+
 require "rails"
 require "active_record/railtie"
 # require "active_storage/engine"
@@ -12,8 +18,11 @@ require "active_job/railtie"
 require "rails/test_unit/railtie"
 # require "sprockets/railtie"
 
+# Load the gems for the current Rails environment from the Gemfile.
 Bundler.require(*Rails.groups)
 
+# Load the default Danbooru configuration from config/danbooru_default_config.rb and the custom config from
+# config/danbooru_local_config.rb.
 begin
   require_relative "danbooru_default_config"
   require_relative ENV.fetch("DANBOORU_CONFIG_FILE", "danbooru_local_config")

config/boot.rb

@@ -1,4 +1,14 @@
+# This is the first file that runs during Rails boot. The next files to run are
+# config/application.rb, then config/environment.rb.
+#
+# @see https://guides.rubyonrails.org/initialization.html
+# @see https://github.com/Shopify/bootsnap
+
 ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../Gemfile', __dir__)
 
-require "bundler/setup" # Set up gems listed in the Gemfile.
-require "bootsnap/setup" # Speed up boot time by caching expensive operations.
+# Set up the load path for gems listed in the Gemfile. Does not actually load the gems; that happens in
+# config/application.rb.
+require "bundler/setup"
+
+# Speed up boot time by caching expensive operations.
+require "bootsnap/setup"

config/danbooru_default_config.rb

@@ -1,3 +1,26 @@
+# This file contains all the configuration settings for Danbooru.
+#
+# Don't edit this file. Instead, to configure your Danbooru instance, copy this
+# file to config/danbooru_local_config.rb and edit that. Remove all settings you
+# don't need to change, and edit only the settings you do need to change.
+#
+# You can also use environment variables to change settings on the command line.
+# For example, to change the site name, you could do:
+#
+#     DANBOORU_APP_NAME=MyBooru bin/rails server
+#
+# This works with nearly any setting. Just take the setting name, uppercase it,
+# and add DANBOORU_ to the front. More examples:
+#
+#     DANBOORU_CANONICAL_URL=https://booru.example.com
+#     DANBOORU_CONTACT_EMAIL=admin@borou.example.com
+#     DANBOORU_DISCORD_SERVER_URL=https://discord.gg/yourbooru
+#
+# Settings from environment variables will override those from the config file.
+#
+# You can also set these environment variables in an envfile instead of the
+# command line. See the .env file in the root project directory for details.
+#
 module Danbooru
   class Configuration
     # A secret key used to encrypt session cookies, among other things.

config/database.yml

@@ -1,9 +1,28 @@
-# Don't edit this file. To override this file, set `DATABASE_URL` in .env.local
-# instead. Example:
+# This file contains database configuration. Don't edit this file. To override
+# this file, set `DATABASE_URL` in .env.local instead.
 #
-#   DATABASE_URL=postgresql://danbooru:password@localhost/danbooru2
+# By default, with no configuration, we try to connect to the Postgres server
+# running on localhost with username `danbooru` and database name `danbooru2`.
 #
-# https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# Example:
+#
+#   # Connect to the database named `danbooru2` via localhost on port 5432
+#   DATABASE_URL=postgresql://localhost/danbooru2
+#
+#   # Connect via Unix domain socket in /var/run/postgresql
+#   # https://zaiste.net/posts/postgresql-unix-socket-tcpip-loopback/
+#   DATABASE_URL=postgresql://%2Fvar%2Frun%2Fpostgresql/danbooru2
+#
+# The general form for a database URL is:
+#
+#   postgresql://[user[:password]@][host][:port][/dbname][?param1=value1&...]`
+#
+# The default is:
+#
+#   postgresql://danbooru@localhost/danbooru2
+#
+# @see https://guides.rubyonrails.org/configuring.html#configuring-a-database
+# @see https://www.postgresql.org/docs/current/libpq-connect.html#id-1.7.3.8.3.6
 
 default: &default
   adapter: postgresql

config/deploy.rb

@@ -1,3 +1,12 @@
+# This file contains configuration settings for deploying Danbooru to the
+# production servers using Capistrano. This is only used by production and
+# shouldn't be edited by end users.
+#
+# @see Capfile
+# @see config/deploy
+# @see lib/capistrano/tasks
+# @see https://capistranorb.com
+
 set :stages, %w(production development staging)
 set :default_stage, "staging"
 set :application, "danbooru"

config/deploy/README.md

@@ -0,0 +1,14 @@
+# Deploy
+
+This directory contains configuration settings for deploying Danbooru to the production servers
+using Capistrano. This is only used by production and shouldn't be edited by end users.
+
+# See also
+
+* [Capfile](../../Capfile)
+* [config/deploy.rb](../deploy.rb)
+* [lib/capistrano/tasks](../../lib/capistrano/tasks)
+
+# External links
+
+* https://capistranorb.com

config/docker/README.md

@@ -0,0 +1,10 @@
+# Docker
+
+This directory contains files for building Docker images for Danbooru.
+
+# External links
+
+* https://docs.docker.com/get-started/
+* https://docs.docker.com/engine/reference/commandline/cli/
+* https://docs.docker.com/engine/reference/builder/
+* https://hub.docker.com/r/evazion/danbooru

config/environments/README.md

@@ -0,0 +1,15 @@
+# Environments
+
+This directory contains environment-specific Rails configuration. This lets us have different
+configuration settings in development, test, and production modes.
+
+Universal Rails configuration goes in [config/application.rb](../application.rb) or in
+[config/initializers](../initializers).
+
+# See also
+
+* [config/application.rb](../application.rb)
+
+# External links
+
+* https://guides.rubyonrails.org/configuring.html#creating-rails-environments

config/initializers/README.md

@@ -0,0 +1,15 @@
+# Initializers
+
+This directory contains initializers run by Rails during bootup. Initializers are generally used to
+configure libraries or other global settings during application boot.
+
+# See also
+
+* [config/boot.rb](../boot.rb)
+* [config/application.rb](../application.rb)
+* [config/environment.rb](../environment.rb)
+
+# External links
+
+* https://guides.rubyonrails.org/configuring.html#using-initializer-files
+* https://guides.rubyonrails.org/initialization.html

config/puma.rb

@@ -1,3 +1,10 @@
+# This file contains configuration settings for the Puma web server. These
+# settings apply when running Danbooru with `bin/rails server`. In production,
+# Danbooru currently uses Unicorn instead of Puma.
+#
+# @see https://puma.io
+# @see https://github.com/puma/puma
+
 # Puma can serve each request in a thread from an internal thread pool.
 # The `threads` method setting takes two numbers: a minimum and maximum.
 # Any libraries that use thread pools should be configured to match

config/routes.rb

@@ -1,3 +1,12 @@
+# This file contains configuration for Danbooru's URL routes. It defines all the
+# URL endpoints and HTTP redirects used by Danbooru.
+#
+# A list of routes can be found at http://localhost:3000/rails/info/routes when
+# running the server in development mode. You can also run `bin/rails routes` to
+# produce a list of routes.
+#
+# @see https://guides.rubyonrails.org/routing.html
+# @see http://localhost:3000/rails/info/routes
 Rails.application.routes.draw do
   resources :posts, only: [:index, :show, :update, :destroy] do
     get :random, on: :collection

config/schedule.rb

@@ -1,3 +1,9 @@
+# This file is used by the `whenver` gem to generate a crontab that runs
+# Danbooru's maintenance tasks.
+#
+# @see app/logical/danbooru_maintenance.rb
+# @see https://github.com/javan/whenever
+
 # this is used in config/environments/production.rb.
 env "RAILS_LOG_TO_STDOUT", "true"
 

config/solargraph.rb

@@ -1,5 +1,9 @@
-# https://solargraph.org/guides/rails
-# https://gist.github.com/castwide/28b349566a223dfb439a337aea29713e
+# This file is used by the Solargraph language server to add better knowledge of
+# Rails for intellisense purposes for editors like VS Code or Vim that have Ruby
+# language server support configured.
+#
+# @see https://solargraph.org/guides/rails
+# @see https://gist.github.com/castwide/28b349566a223dfb439a337aea29713e
 #
 # The following comments fill some of the gaps in Solargraph's understanding of
 # Rails apps. Since they're all in YARD, they get mapped in Solargraph but

config/spring.rb

@@ -1,3 +1,7 @@
+# This file configures Spring, the Rails application preloader.
+#
+# @see https://github.com/rails/spring
+
 %w[
   .ruby-version
   .rbenv-vars

config/unicorn/README.md

@@ -0,0 +1,12 @@
+# Unicorn
+
+This directory contains configuration files for Unicorn, the web server that Danbooru uses in production.
+
+# See also
+
+* [config/puma.rb](../puma.rb)
+
+# External links
+
+* https://yhbt.net/unicorn/README.html
+* https://github.com/defunkt/unicorn

config/webpack/README.md

@@ -0,0 +1,16 @@
+# Webpack
+
+This directory contains configuration for Webpack. Webpack is used to bundle Javascript and CSS
+assets in production. In Rails, Webpack is wrapped by Webpacker, a layer that tries to provide
+sensible defaults for Webpack.
+
+# See also
+
+* [app/javascript](../../app/javascript)
+* [config/webpacker.yml](../webpacker.yml)
+
+# External links
+
+* https://guides.rubyonrails.org/webpacker.html
+* https://github.com/rails/webpacker#webpack-configuration
+* https://webpack.js.org/configuration/

config/webpack/base.js

@@ -13,6 +13,7 @@ module.exports = merge(webpackConfig, {
   },
   module: {
     rules: [{
+      // https://github.com/usabilityhub/rails-erb-loader
       test: /.erb$/,
       enforce: "pre",
       exclude: /node_modules/,

config/webpack/development.js

@@ -1,3 +1,5 @@
+// @see https://github.com/webpack-contrib/eslint-webpack-plugin
+
 process.env.NODE_ENV = process.env.NODE_ENV || 'development'
 
 const { merge } = require('@rails/webpacker')

config/webpacker.yml

@@ -1,4 +1,10 @@
+# This file configures Webpacker, the Rails wrapper around Webpack. Webpack is
+# used to bundle Javascript and CSS assets.
+#
 # Note: You must restart bin/webpack-dev-server for changes to take effect
+#
+# @see https://github.com/rails/webpacker
+# @see https://edgeguides.rubyonrails.org/webpacker.html
 
 default: &default
   source_path: app/javascript