Add support for git-worktree

Main reason we didn't previously support work trees was because we had
assumed that the `.git` directory was always located in the repository
root. With separate work trees, this is not necessarily the case.

Add support by using Git commands to fetch the location of the GIT_DIR
instead of trying to determine it ourself.

README.md

@@ -57,13 +57,6 @@ This project aims to support the following Ruby runtimes on both \*nix and Windo
 
 * MRI 2.x
 
-## Limitations
-
-Overcommit does not currently support
-[`git-worktree`](https://git-scm.com/docs/git-worktree) (introduced in Git 2.5),
-but there is an [open issue](https://github.com/brigade/overcommit/issues/336)
-tracking progress on adding support.
-
 ### Dependencies
 
 Some of the hooks have third-party dependencies. For example, to lint your

lib/overcommit/git_config.rb

@@ -14,7 +14,7 @@ def comment_character
     def hooks_path
       path = `git config --get core.hooksPath`.chomp
       return File.join(Overcommit::Utils.git_dir, 'hooks') if path.empty?
-      File.absolute_path(path)
+      File.absolute_path(path, Dir.pwd)
     end
   end
 end

lib/overcommit/utils.rb

@@ -43,38 +43,29 @@ def script_path(script)
       def repo_root
         @repo_root ||=
           begin
-            git_dir = Pathname.new(File.expand_path('.')).enum_for(:ascend).find do |path|
-              File.exist?(File.join(path, '.git'))
+            result = execute(%w[git rev-parse --show-toplevel])
+            unless result.success?
+              raise Overcommit::Exceptions::InvalidGitRepo,
+                    'Unable to determine location of GIT_DIR. ' \
+                    'Not a recognizable Git repository!'
             end
-
-            unless git_dir
-              raise Overcommit::Exceptions::InvalidGitRepo, 'no .git directory found'
-            end
-
-            git_dir.to_s
+            result.stdout.chomp("\n")
           end
       end
 
       # Returns an absolute path to the .git directory for a repo.
       #
-      # @param repo_dir [String] root directory of git repo
       # @return [String]
-      def git_dir(repo_dir = repo_root)
+      def git_dir
         @git_dir ||=
           begin
-            git_dir = File.expand_path('.git', repo_dir)
-
-            # .git could also be a file that contains the location of the git directory
-            unless File.directory?(git_dir)
-              git_dir = File.read(git_dir)[/^gitdir: (.*)$/, 1]
-
-              # Resolve relative paths
-              unless git_dir.start_with?('/')
-                git_dir = File.expand_path(git_dir, repo_dir)
-              end
+            result = execute(%w[git rev-parse --git-common-dir])
+            unless result.success?
+              raise Overcommit::Exceptions::InvalidGitRepo,
+                    'Unable to determine location of GIT_DIR. ' \
+                    'Not a recognizable Git repository!'
             end
-
-            git_dir
+            File.expand_path(result.stdout.chomp("\n"), Dir.pwd)
           end
       end
 

spec/overcommit/utils_spec.rb

@@ -52,27 +52,13 @@
       end
     end
 
-    context 'when .git is a file' do
-      before do
-        FileUtils.rm_rf('.git', secure: true)
-        echo("gitdir: #{git_dir_path}", '.git')
-      end
+    context 'when .git directory is not located in the repository' do
+      let(:git_dir) { Dir.mktmpdir }
+      let(:repo_dir) { repo(git_dir: git_dir) }
 
-      context 'and is a relative path' do
-        let(:git_dir_path) { '../.git' }
-
-        it 'returns the path contained in the file' do
-          # realpath is so spec passes on Mac OS X
-          subject.should == File.join(File.realpath(File.dirname(repo_dir)), '.git')
-        end
-      end
-
-      context 'and is an absolute path' do
-        let(:git_dir_path) { '/some/arbitrary/path/.git' }
-
-        it 'returns the path contained in the file' do
-          subject.should == git_dir_path
-        end
+      it 'returns the path of the external Git directory' do
+        # realpath is so spec passes on Mac OS X
+        subject.should == File.realpath(git_dir)
       end
     end
   end

spec/support/git_spec_helpers.rb

@@ -11,7 +11,12 @@ module GitSpecHelpers
   # @return [String] path of the repository
   def repo(options = {})
     directory('some-repo') do
-      `git init --template="#{options[:template_dir]}"`
+      create_cmd = %w[git init]
+      create_cmd += ['--template', options[:template_dir]] if options[:template_dir]
+      create_cmd += ['--separate-git-dir', options[:git_dir]] if options[:git_dir]
+
+      result = Overcommit::Utils.execute(create_cmd)
+      raise "Unable to create repo: #{result.stderr}" unless result.success?
 
       # Need to define user info since some CI contexts don't have defaults set
       `git config --local user.name "Overcommit Tester"`