Move location of buildpacks cache directory

- This won't affect anything, but protects against buildpacks that blow
away the entire cache directory rather than just things they created

Related: heroku/heroku-buildpack-go#187

lib/slugbuilder/builder.rb

@@ -7,17 +7,17 @@ module Slugbuilder
   class Builder
     def initialize(repo:, git_ref:, stdout: $stdout)
       @stdout = stdout
-      @base_dir = Slugbuilder.config.base_dir
+      @base_dir = Shellwords.escape(Slugbuilder.config.base_dir)
       @cache_dir = Shellwords.escape(Slugbuilder.config.cache_dir)
-      @output_dir = Slugbuilder.config.output_dir
-      @buildpacks_dir = File.join(@cache_dir, 'buildpacks')
+      @output_dir = Shellwords.escape(Slugbuilder.config.output_dir)
+      @buildpacks_dir = File.join(@base_dir, 'buildpacks')
       @env_dir = File.join(@base_dir, 'environment')
       repo_matches = parse_git_url(repo)
       @repo = "#{repo_matches[:org]}/#{repo_matches[:name]}"
       @git_url = normalize_git_url(repo)
       @git_ref = git_ref
-      @git_dir = Shellwords.escape(File.join(@base_dir, 'git', @repo))
-      @build_dir = Shellwords.escape(File.join(@base_dir, @repo, git_ref))
+      @git_dir = File.join(@base_dir, 'git', @repo)
+      @build_dir = File.join(@base_dir, @repo, git_ref)
 
       setup
 
@@ -83,6 +83,8 @@ def with_clean_env
 
     def wipe_cache
       FileUtils.rm_rf(@cache_dir)
+      FileUtils.rm_rf(@buildpacks_dir)
+      FileUtils.mkdir_p(@cache_dir)
       FileUtils.mkdir_p(@buildpacks_dir)
     end
 
@@ -136,6 +138,7 @@ def set_environment
     end
 
     def create_dirs
+      FileUtils.mkdir_p(@cache_dir)
       FileUtils.mkdir_p(@base_dir)
       FileUtils.mkdir_p(@buildpacks_dir)
       FileUtils.mkdir_p(@output_dir)

spec/slugbuilder/builder_spec.rb

@@ -28,6 +28,7 @@
 
     it 'creates directories' do
       expect(Dir['/tmp/*']).to include('/tmp/slugbuilder', '/tmp/slugbuilder-cache', '/tmp/slugs')
+      expect(Dir['/tmp/slugbuilder/*']).to include('/tmp/slugbuilder/buildpacks')
     end
 
     it 'pulls down git repo and copies to build directory' do
@@ -100,20 +101,20 @@
       Slugbuilder.config.buildpacks = ['https://github.com/heroku/heroku-buildpack-nodejs.git']
       builder.build(clear_cache: true)
       # make sure that ruby buildpack is no longer cached
-      expect(Dir['/tmp/slugbuilder-cache/buildpacks/*']).to eq(['/tmp/slugbuilder-cache/buildpacks/heroku__heroku-buildpack-nodejs'])
+      expect(Dir['/tmp/slugbuilder/buildpacks/*']).to eq(['/tmp/slugbuilder/buildpacks/heroku__heroku-buildpack-nodejs'])
     end
 
     it 'allows specifying the buildpacks for a build' do
       builder.build
-      expect(Dir['/tmp/slugbuilder-cache/buildpacks/*']).to eq(['/tmp/slugbuilder-cache/buildpacks/heroku__heroku-buildpack-nodejs'])
+      expect(Dir['/tmp/slugbuilder/buildpacks/*']).to eq(['/tmp/slugbuilder/buildpacks/heroku__heroku-buildpack-nodejs'])
       buildpacks = [
         'https://github.com/heroku/heroku-buildpack-nodejs.git',
         'https://github.com/heroku/heroku-buildpack-ruby.git'
       ]
       builder.build(buildpacks: buildpacks)
-      expect(Dir['/tmp/slugbuilder-cache/buildpacks/*']).to eq([
-        '/tmp/slugbuilder-cache/buildpacks/heroku__heroku-buildpack-nodejs',
-        '/tmp/slugbuilder-cache/buildpacks/heroku__heroku-buildpack-ruby'
+      expect(Dir['/tmp/slugbuilder/buildpacks/*']).to eq([
+        '/tmp/slugbuilder/buildpacks/heroku__heroku-buildpack-nodejs',
+        '/tmp/slugbuilder/buildpacks/heroku__heroku-buildpack-ruby'
       ])
     end
 
@@ -123,10 +124,10 @@
         'git@github.com:heroku/heroku-buildpack-ruby.git#5a1ca011c568321077101028a11d24e6e09f1c36'
       ]
       builder.build(buildpacks: buildpacks)
-      expect(Dir['/tmp/slugbuilder-cache/buildpacks/*']).to eq([
-        '/tmp/slugbuilder-cache/buildpacks/heroku__heroku-buildpack-nodejs',
-        '/tmp/slugbuilder-cache/buildpacks/heroku__heroku-buildpack-ruby',
-        '/tmp/slugbuilder-cache/buildpacks/heroku__heroku-buildpack-ruby5a1ca011c568321077101028a11d24e6e09f1c36'
+      expect(Dir['/tmp/slugbuilder/buildpacks/*']).to eq([
+        '/tmp/slugbuilder/buildpacks/heroku__heroku-buildpack-nodejs',
+        '/tmp/slugbuilder/buildpacks/heroku__heroku-buildpack-ruby',
+        '/tmp/slugbuilder/buildpacks/heroku__heroku-buildpack-ruby5a1ca011c568321077101028a11d24e6e09f1c36'
       ])
     end