Add Spring.spawn_on_env

Currently, it isn't possible for Spring to create multiple applications
for a given environment variable value. For example, you might want to
run an application with and without certain features enabled in the same
rails env.

Configuration must be set in config/spring_client.rb

lib/spring/application.rb

@@ -28,6 +28,10 @@ def state!(val)
       @interrupt.last.write "."
     end
 
+    def spawn_env
+      JSON.load(ENV["SPRING_SPAWN_ENV"].dup).map { |key, value| "#{key}=#{value}"  }.join(", ")
+    end
+
     def app_env
       ENV['RAILS_ENV']
     end

lib/spring/application/boot.rb

@@ -11,9 +11,15 @@
 
 Signal.trap("TERM") { app.terminate }
 
-Spring::ProcessTitleUpdater.run { |distance|
-  "spring app    | #{app.app_name} | started #{distance} ago | #{app.app_env} mode"
-}
+Spring::ProcessTitleUpdater.run do |distance|
+  attributes = [
+    app.app_name,
+    "started #{distance} ago",
+    "#{app.app_env} mode",
+    app.spawn_env,
+  ]
+  "spring app    | #{attributes.join(" | ")}"
+end
 
 app.eager_preload if ENV.delete("SPRING_PRELOAD") == "1"
 app.run

lib/spring/application_manager.rb

@@ -1,9 +1,10 @@
 module Spring
   class ApplicationManager
-    attr_reader :pid, :child, :app_env, :spring_env, :status
+    attr_reader :pid, :child, :app_env, :spawn_env, :spring_env, :status
 
-    def initialize(app_env, spring_env)
+    def initialize(app_env, spawn_env, spring_env)
       @app_env    = app_env
+      @spawn_env  = spawn_env
       @spring_env = spring_env
       @mutex      = Mutex.new
       @state      = :running
@@ -100,7 +101,9 @@ def start_child(preload = false)
             "RAILS_ENV"           => app_env,
             "RACK_ENV"            => app_env,
             "SPRING_ORIGINAL_ENV" => JSON.dump(Spring::ORIGINAL_ENV),
-            "SPRING_PRELOAD"      => preload ? "1" : "0"
+            "SPRING_PRELOAD"      => preload ? "1" : "0",
+            "SPRING_SPAWN_ENV"    => JSON.dump(spawn_env),
+            **spawn_env,
           },
           "ruby",
           *(bundler_dir != RbConfig::CONFIG["rubylibdir"] ? ["-I", bundler_dir] : []),

lib/spring/client/run.rb

@@ -132,7 +132,7 @@ def verify_server_version
 
       def connect_to_application(client)
         server.send_io client
-        send_json server, "args" => args, "default_rails_env" => default_rails_env
+        send_json server, "args" => args, "default_rails_env" => default_rails_env, "spawn_env" => spawn_env
 
         if IO.select([server], [], [], CONNECT_TIMEOUT)
           server.gets or raise CommandNotFound
@@ -232,6 +232,10 @@ def send_json(socket, data)
       def default_rails_env
         ENV['RAILS_ENV'] || ENV['RACK_ENV'] || 'development'
       end
+
+      def spawn_env
+        ENV.slice(*Spring.spawn_on_env)
+      end
     end
   end
 end

lib/spring/configuration.rb

@@ -32,6 +32,10 @@ def after_fork(&block)
       after_fork_callbacks << block
     end
 
+    def spawn_on_env
+      @spawn_on_env ||= []
+    end
+
     def verify_environment
       application_root_path
     end

lib/spring/server.rb

@@ -19,7 +19,9 @@ def self.boot(options = {})
     def initialize(options = {})
       @foreground   = options.fetch(:foreground, false)
       @env          = options[:env] || default_env
-      @applications = Hash.new { |h, k| h[k] = ApplicationManager.new(k, env) }
+      @applications = Hash.new do |hash, key|
+        hash[key] = ApplicationManager.new(*key, env)
+      end
       @pidfile      = env.pidfile_path.open('a')
       @mutex        = Mutex.new
     end
@@ -57,12 +59,12 @@ def serve(client)
       app_client = client.recv_io
       command    = JSON.load(client.read(client.gets.to_i))
 
-      args, default_rails_env = command.values_at('args', 'default_rails_env')
+      args, default_rails_env, spawn_env = command.values_at('args', 'default_rails_env', 'spawn_env')
 
       if Spring.command?(args.first)
         log "running command #{args.first}"
         client.puts
-        client.puts @applications[rails_env_for(args, default_rails_env)].run(app_client)
+        client.puts @applications[rails_env_for(args, default_rails_env, spawn_env)].run(app_client)
       else
         log "command not found #{args.first}"
         client.close
@@ -73,8 +75,8 @@ def serve(client)
       redirect_output
     end
 
-    def rails_env_for(args, default_rails_env)
-      Spring.command(args.first).env(args.drop(1)) || default_rails_env
+    def rails_env_for(args, default_rails_env, spawn_env)
+      [Spring.command(args.first).env(args.drop(1)) || default_rails_env, spawn_env]
     end
 
     # Boot the server into the process group of the current session.