Repo: handle worktrees better

This makes Repo("foo") work when foo/.git is a file of the form created
by "git worktree add", i.e. it's a text file that says:

gitdir: /home/me/project/.git/worktrees/bar

and where /home/me/project/.git/ is the nominal gitdir, but
/home/me/project/.git/worktrees/bar has this worktree's HEAD etc and a
"gitdir" file that contains the path of foo/.git .

Signed-off-by: Peter Jones <pjones@redhat.com>

6 files changed, 105 insertions, 19 deletions

diff --git a/AUTHORS b/AUTHORS
index 781695ba..ad7c452c 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -18,5 +18,6 @@ Contributors are:
 -Bernard `Guyzmo` Pratz <guyzmo+gitpython+pub@m0g.net>
 -Timothy B. Hartman <tbhartman _at_ gmail.com>
 -Konstantin Popov <konstantin.popov.89 _at_ yandex.ru>
+-Peter Jones <pjones _at_ redhat.com>
 
 Portions derived from other open source works and are clearly marked.
diff --git a/git/refs/symbolic.py b/git/refs/symbolic.py
index 22b7c53e..90ecb62c 100644
--- a/git/refs/symbolic.py
+++ b/git/refs/symbolic.py
@@ -75,7 +75,12 @@ class SymbolicReference(object):
 
     @classmethod
     def _get_packed_refs_path(cls, repo):
-        return osp.join(repo.git_dir, 'packed-refs')
+        try:
+            commondir = open(osp.join(repo.git_dir, 'commondir'), 'rt').readlines()[0].strip()
+        except (OSError, IOError):
+            commondir = '.'
+        repodir = osp.join(repo.git_dir, commondir)
+        return osp.join(repodir, 'packed-refs')
 
     @classmethod
     def _iter_packed_refs(cls, repo):
@@ -122,13 +127,13 @@ class SymbolicReference(object):
         # END recursive dereferencing
 
     @classmethod
-    def _get_ref_info(cls, repo, ref_path):
+    def _get_ref_info_helper(cls, repo, repodir, ref_path):
         """Return: (str(sha), str(target_ref_path)) if available, the sha the file at
         rela_path points to, or None. target_ref_path is the reference we
         point to, or None"""
         tokens = None
         try:
-            with open(osp.join(repo.git_dir, ref_path), 'rt') as fp:
+            with open(osp.join(repodir, ref_path), 'rt') as fp:
                 value = fp.read().rstrip()
             # Don't only split on spaces, but on whitespace, which allows to parse lines like
             # 60b64ef992065e2600bfef6187a97f92398a9144                branch 'master' of git-server:/path/to/repo
@@ -159,6 +164,22 @@ class SymbolicReference(object):
 
         raise ValueError("Failed to parse reference information from %r" % ref_path)
 
+    @classmethod
+    def _get_ref_info(cls, repo, ref_path):
+        """Return: (str(sha), str(target_ref_path)) if available, the sha the file at
+        rela_path points to, or None. target_ref_path is the reference we
+        point to, or None"""
+        try:
+            return cls._get_ref_info_helper(repo, repo.git_dir, ref_path)
+        except ValueError:
+            try:
+                commondir = open(osp.join(repo.git_dir, 'commondir'), 'rt').readlines()[0].strip()
+            except (OSError, IOError):
+                commondir = '.'
+
+            repodir = osp.join(repo.git_dir, commondir)
+            return cls._get_ref_info_helper(repo, repodir, ref_path)
+
     def _get_object(self):
         """
         :return:
diff --git a/git/repo/base.py b/git/repo/base.py
index 2f67a341..28bb2a5d 100644
--- a/git/repo/base.py
+++ b/git/repo/base.py
@@ -32,7 +32,7 @@ from git.remote import Remote, add_progress, to_progress_instance
 from git.util import Actor, finalize_process, decygpath, hex_to_bin
 import os.path as osp
 
-from .fun import rev_parse, is_git_dir, find_submodule_git_dir, touch
+from .fun import rev_parse, is_git_dir, find_submodule_git_dir, touch, find_worktree_git_dir
 import gc
 import gitdb
 
@@ -138,10 +138,15 @@ class Repo(object):
                 self._working_tree_dir = os.getenv('GIT_WORK_TREE', os.path.dirname(self.git_dir))
                 break
 
-            sm_gitpath = find_submodule_git_dir(osp.join(curpath, '.git'))
+            dotgit = osp.join(curpath, '.git')
+            sm_gitpath = find_submodule_git_dir(dotgit)
             if sm_gitpath is not None:
                 self.git_dir = osp.normpath(sm_gitpath)
-            sm_gitpath = find_submodule_git_dir(osp.join(curpath, '.git'))
+
+            sm_gitpath = find_submodule_git_dir(dotgit)
+            if sm_gitpath is None:
+                sm_gitpath = find_worktree_git_dir(dotgit)
+
             if sm_gitpath is not None:
                 self.git_dir = _expand_path(sm_gitpath)
                 self._working_tree_dir = curpath
diff --git a/git/repo/fun.py b/git/repo/fun.py
index 39e55880..6aefd9d6 100644
--- a/git/repo/fun.py
+++ b/git/repo/fun.py
@@ -1,5 +1,6 @@
 """Package with general repository related functions"""
 import os
+import stat
 from string import digits
 
 from git.compat import xrange
@@ -17,7 +18,7 @@ from git.cmd import Git
 
 
 __all__ = ('rev_parse', 'is_git_dir', 'touch', 'find_submodule_git_dir', 'name_to_object', 'short_to_long', 'deref_tag',
-           'to_commit')
+           'to_commit', 'find_worktree_git_dir')
 
 
 def touch(filename):
@@ -47,6 +48,25 @@ def is_git_dir(d):
     return False
 
 
+def find_worktree_git_dir(dotgit):
+    """Search for a gitdir for this worktree."""
+    try:
+        statbuf = os.stat(dotgit)
+    except OSError:
+        return None
+    if not stat.S_ISREG(statbuf.st_mode):
+        return None
+
+    try:
+        lines = open(dotgit, 'r').readlines()
+        for key, value in [line.strip().split(': ') for line in lines]:
+            if key == 'gitdir':
+                return value
+    except ValueError:
+        pass
+    return None
+
+
 def find_submodule_git_dir(d):
     """Search for a submodule repo."""
     if is_git_dir(d):
diff --git a/git/test/test_fun.py b/git/test/test_fun.py
index b472fe19..5e32a1f9 100644
--- a/git/test/test_fun.py
+++ b/git/test/test_fun.py
@@ -1,10 +1,14 @@
 from io import BytesIO
 from stat import S_IFDIR, S_IFREG, S_IFLNK
+from os import stat
+import os.path as osp
+
 try:
-    from unittest import skipIf
+    from unittest import skipIf, SkipTest
 except ImportError:
-    from unittest2 import skipIf
+    from unittest2 import skipIf, SkipTest
 
+from git import Git
 from git.compat import PY3
 from git.index import IndexFile
 from git.index.fun import (
@@ -14,13 +18,18 @@ from git.objects.fun import (
     traverse_tree_recursive,
     traverse_trees_recursive,
     tree_to_stream,
-    tree_entries_from_data
+    tree_entries_from_data,
+)
+from git.repo.fun import (
+    find_worktree_git_dir
 )
 from git.test.lib import (
+    assert_true,
     TestBase,
-    with_rw_repo
+    with_rw_repo,
+    with_rw_directory
 )
-from git.util import bin_to_hex
+from git.util import bin_to_hex, cygpath, join_path_native
 from gitdb.base import IStream
 from gitdb.typ import str_tree_type
 
@@ -254,6 +263,29 @@ class TestFun(TestBase):
             assert entries
         # END for each commit
 
+    @with_rw_directory
+    def test_linked_worktree_traversal(self, rw_dir):
+        """Check that we can identify a linked worktree based on a .git file"""
+        git = Git(rw_dir)
+        if git.version_info[:3] < (2, 5, 1):
+            raise SkipTest("worktree feature unsupported")
+
+        rw_master = self.rorepo.clone(join_path_native(rw_dir, 'master_repo'))
+        branch = rw_master.create_head('aaaaaaaa')
+        worktree_path = join_path_native(rw_dir, 'worktree_repo')
+        if Git.is_cygwin():
+            worktree_path = cygpath(worktree_path)
+        rw_master.git.worktree('add', worktree_path, branch.name)
+
+        dotgit = osp.join(worktree_path, ".git")
+        statbuf = stat(dotgit)
+        assert_true(statbuf.st_mode & S_IFREG)
+
+        gitdir = find_worktree_git_dir(dotgit)
+        self.assertIsNotNone(gitdir)
+        statbuf = stat(gitdir)
+        assert_true(statbuf.st_mode & S_IFDIR)
+
     @skipIf(PY3, 'odd types returned ... maybe figure it out one day')
     def test_tree_entries_from_data_with_failing_name_decode_py2(self):
         r = tree_entries_from_data(b'100644 \x9f\0aaa')
diff --git a/git/test/test_repo.py b/git/test/test_repo.py
index 86019b73..a6be4e66 100644
--- a/git/test/test_repo.py
+++ b/git/test/test_repo.py
@@ -22,6 +22,7 @@ from git import (
     NoSuchPathError,
     Head,
     Commit,
+    Object,
     Tree,
     IndexFile,
     Git,
@@ -911,22 +912,28 @@ class TestRepo(TestBase):
             self.assertRaises(GitCommandError, repo.is_ancestor, i, j)
 
     @with_rw_directory
-    def test_work_tree_unsupported(self, rw_dir):
+    def test_git_work_tree_dotgit(self, rw_dir):
+        """Check that we find .git as a worktree file and find the worktree
+        based on it."""
         git = Git(rw_dir)
         if git.version_info[:3] < (2, 5, 1):
             raise SkipTest("worktree feature unsupported")
 
         rw_master = self.rorepo.clone(join_path_native(rw_dir, 'master_repo'))
-        rw_master.git.checkout('HEAD~10')
+        branch = rw_master.create_head('aaaaaaaa')
         worktree_path = join_path_native(rw_dir, 'worktree_repo')
         if Git.is_cygwin():
             worktree_path = cygpath(worktree_path)
-        try:
-            rw_master.git.worktree('add', worktree_path, 'master')
-        except Exception as ex:
-            raise AssertionError(ex, "It's ok if TC not running from `master`.")
+        rw_master.git.worktree('add', worktree_path, branch.name)
+
+        # this ensures that we can read the repo's gitdir correctly
+        repo = Repo(worktree_path)
+        self.assertIsInstance(repo, Repo)
 
-        self.failUnlessRaises(InvalidGitRepositoryError, Repo, worktree_path)
+        # this ensures we're able to actually read the refs in the tree, which
+        # means we can read commondir correctly.
+        commit = repo.head.commit
+        self.assertIsInstance(commit, Object)
 
     @with_rw_directory
     def test_git_work_tree_env(self, rw_dir):