Fix debug out put for in_directory_fork (#146)

When an error is raised inside of `in_directory_fork` it writes over the existing contents so if there's any debug output that was added it gets written over.

This fixes that behavior by making stdout and stderr append to the log file instead of

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## HEAD
 
+- Fix App#in_directory_fork not receiving debugging output when an error is raised (https://github.com/heroku/hatchet/pull/146)
 - Do not create CI tarball inside cwd to prevent tar "file changed as we read it" warnings.
 
 ## 7.3.1

lib/hatchet/app.rb

@@ -387,8 +387,8 @@ def in_directory
     def in_directory_fork(&block)
       Tempfile.create("stdout") do |tmp_file|
         pid = fork do
-          $stdout.reopen(tmp_file, "w")
-          $stderr.reopen(tmp_file, "w")
+          $stdout.reopen(tmp_file, "a")
+          $stderr.reopen(tmp_file, "a")
           $stdout.sync = true
           $stderr.sync = true
           in_directory do |dir|

spec/hatchet/local_repo_spec.rb

@@ -11,6 +11,15 @@
     expect(ENV[env_name]).to eq(env_name)
   end
 
+  it "in directory fork captures stdout even when there is an error" do
+    expect {
+      Hatchet::App.new("default_ruby").in_directory_fork do
+        puts "hello_there"
+        raise "error"
+      end
+    }.to raise_error(/hello_there/)
+  end
+
   it "repos checked into git" do
     begin
       fixture_dir = "repo_fixtures/different-folder-for-checked-in-repos/default_ruby"