Add ability to log from the Ruby Buildpack

.gitignore

@@ -6,3 +6,4 @@ vendor/bundle/*
 .ruby-version
 buildpacks/*
 .anvil/
+tmp/*.log

.travis.yml

@@ -1,6 +1,6 @@
 language: ruby
 rvm:
-- 2.4.1
+- 2.4.3
 before_script: bundle exec rake hatchet:setup_travis
 script: bundle exec parallel_rspec -n 11 spec/
 env:

Rakefile

@@ -2,6 +2,8 @@ require "fileutils"
 require "tmpdir"
 require 'hatchet/tasks'
 
+ENV["BUILDPACK_LOG_FILE"] ||= "tmp/buildpack.log"
+
 S3_BUCKET_NAME  = "heroku-buildpack-ruby"
 VENDOR_URL      = "https://s3.amazonaws.com/#{S3_BUCKET_NAME}"
 

lib/language_pack/base.rb

@@ -93,6 +93,7 @@ def compile
         puts @deprecations.join("\n")
       end
     end
+    mcount "success.ruby"
   end
 
   def write_release_yaml

lib/language_pack/shell_helpers.rb

@@ -14,6 +14,18 @@ module LanguagePack
   module ShellHelpers
     @@user_env_hash = {}
 
+    def mcount(key, value = 1)
+      private_log("count", key => value)
+    end
+
+    def mmeasure(key, value)
+      private_log("measure", key => value)
+    end
+
+    def munique(key, value)
+      private_log("unique", key => value)
+    end
+
     def self.user_env_hash
       @@user_env_hash
     end
@@ -149,5 +161,14 @@ def deprecate(message)
     def noshellescape(string)
       NoShellEscape.new(string)
     end
+
+    private
+      def private_log(name, key_value_hash)
+        File.open(ENV["BUILDPACK_LOG_FILE"], "a+") do |f|
+          key_value_hash.each do |key, value|
+            f.puts "#{name}##{ENV["BPLOG_PREFIX"]}#{key}=#{value}"
+          end
+        end
+      end
   end
 end

spec/helpers/shell_spec.rb

@@ -14,6 +14,21 @@ class FakeShell
     include LanguagePack::ShellHelpers
   end
 
+  describe "mcount" do
+    it "logs to a file" do
+      begin
+        original = ENV["BUILDPACK_LOG_FILE"]
+        Tempfile.open("logfile.log") do |f|
+          ENV["BUILDPACK_LOG_FILE"] = f.path
+          FakeShell.new.mcount "foo"
+          expect(File.read(f.path)).to match("count#foo=1")
+        end
+      ensure
+        ENV["BUILDPACK_LOG_FILE"] = original
+      end
+    end
+  end
+
   describe "#command_options_to_string" do
     it "formats ugly keys correctly" do
       env      = {%Q{ un"matched } => "bad key"}