Check that app preload was successful before sending a command.

lib/spring/application.rb

@@ -152,7 +152,18 @@ def serve(client)
       _stdout, stderr, _stdin = streams = 3.times.map { client.recv_io }
       [STDOUT, STDERR, STDIN].zip(streams).each { |a, b| a.reopen(b) }
 
-      preload unless preloaded?
+      if preloaded?
+        client.puts(0) # preload success
+      else
+        begin
+          preload
+          client.puts(0) # preload success
+        rescue Exception
+          log "preload failed"
+          client.puts(1) # preload failure
+          raise
+        end
+      end
 
       args, env = JSON.load(client.read(client.gets.to_i)).values_at("args", "env")
       command   = Spring.command(args.shift)

lib/spring/client/run.rb

@@ -142,12 +142,17 @@ def connect_to_application(client)
       end
 
       def run_command(client, application)
-        log "sending command"
-
         application.send_io STDOUT
         application.send_io STDERR
         application.send_io STDIN
 
+        log "waiting for the application to be preloaded"
+        preload_status = application.gets
+        preload_status = preload_status.chomp if preload_status
+        log "app preload status: #{preload_status}"
+        exit 1 if preload_status == "1"
+
+        log "sending command"
         send_json application, "args" => args, "env" => ENV.to_hash
 
         pid = server.gets

test/support/acceptance_test.rb

@@ -98,6 +98,15 @@ def without_gem(name)
         end
       end
 
+      test "crash on boot" do
+        app.run app.spring_test_command, env: {
+          "CRASH_ON_BOOT" => "1",
+          # If the command is small enough, it might fit in the socket buffer and writing the command won't block.
+          # So we send a big environment variable to better reproduce the problem.
+          "FOO" => "bar" * 4_000,
+      }
+      end
+
       test "help message when called without arguments" do
         assert_success "bin/spring", stdout: 'Usage: spring COMMAND [ARGS]'
         assert spring_env.server_running?

test/support/application.rb

@@ -113,7 +113,7 @@ def run(command, opts = {})
 
         Bundler.with_clean_env do
           Process.spawn(
-            env,
+            env.merge(opts[:env] || {}),
             command.to_s,
             out:   stdout.last,
             err:   stderr.last,

test/support/application_generator.rb

@@ -54,6 +54,8 @@ def generate_files
 
         append_to_file(application.gemfile, "gem 'spring', '#{Spring::VERSION}'")
 
+        append_to_file(application.path("config/boot.rb"), "raise 'BOOM' if ENV['CRASH_ON_BOOT']")
+
         rewrite_file(application.gemfile) do |c|
           c.sub!("https://rubygems.org", "http://rubygems.org")
           c.gsub!(/(gem '(byebug|web-console|sdoc|jbuilder)')/, "# \\1")