git-p4: support git worktrees

git-p4 would attempt to find the git directory using
its own specific code, which did not know about git
worktrees.

Rework it to use "git rev-parse --git-dir" instead.

Add test cases for worktree usage and specifying
git directory via --git-dir and $GIT_DIR.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -85,6 +85,16 @@ def p4_build_cmd(cmd):
         real_cmd += cmd
     return real_cmd
 
+def git_dir(path):
+    """ Return TRUE if the given path is a git directory (/path/to/dir/.git).
+        This won't automatically add ".git" to a directory.
+    """
+    d = read_pipe(["git", "--git-dir", path, "rev-parse", "--git-dir"], True).strip()
+    if not d or len(d) == 0:
+        return None
+    else:
+        return d
+
 def chdir(path, is_client_path=False):
     """Do chdir to the given path, and set the PWD environment
        variable for use by P4.  It does not look at getcwd() output.
@@ -563,10 +573,7 @@ def currentGitBranch():
         return read_pipe(["git", "name-rev", "HEAD"]).split(" ")[1].strip()
 
 def isValidGitDir(path):
-    if (os.path.exists(path + "/HEAD")
-        and os.path.exists(path + "/refs") and os.path.exists(path + "/objects")):
-        return True;
-    return False
+    return git_dir(path) != None
 
 def parseRevision(ref):
     return read_pipe("git rev-parse %s" % ref).strip()
@@ -3682,6 +3689,7 @@ def main():
         if cmd.gitdir == None:
             cmd.gitdir = os.path.abspath(".git")
             if not isValidGitDir(cmd.gitdir):
+                # "rev-parse --git-dir" without arguments will try $PWD/.git
                 cmd.gitdir = read_pipe("git rev-parse --git-dir").strip()
                 if os.path.exists(cmd.gitdir):
                     cdup = read_pipe("git rev-parse --show-cdup").strip()
@@ -3694,6 +3702,7 @@ def main():
             else:
                 die("fatal: cannot locate git repository at %s" % cmd.gitdir)
 
+        # so git commands invoked from the P4 workspace will succeed
         os.environ["GIT_DIR"] = cmd.gitdir
 
     if not cmd.run(args):

t/t9800-git-p4-basic.sh

@@ -257,6 +257,26 @@ test_expect_success 'submit from detached head' '
 	)
 '
 
+test_expect_success 'submit from worktree' '
+	test_when_finished cleanup_git &&
+	git p4 clone --dest="$git" //depot &&
+	(
+		cd "$git" &&
+		git worktree add ../worktree-test
+	) &&
+	(
+		cd "$git/../worktree-test" &&
+		test_commit "worktree-commit" &&
+		git config git-p4.skipSubmitEdit true &&
+		git p4 submit
+	) &&
+	(
+		cd "$cli" &&
+		p4 sync &&
+		test_path_is_file worktree-commit.t
+	)
+'
+
 test_expect_success 'kill p4d' '
 	kill_p4d
 '

t/t9806-git-p4-options.sh

@@ -269,6 +269,38 @@ test_expect_success 'submit works with two branches' '
 	)
 '
 
+test_expect_success 'use --git-dir option and GIT_DIR' '
+	test_when_finished cleanup_git &&
+	git p4 clone //depot --destination="$git" &&
+	(
+		cd "$git" &&
+		git config git-p4.skipSubmitEdit true &&
+		test_commit first-change &&
+		git p4 submit --git-dir "$git"
+	) &&
+	(
+		cd "$cli" &&
+		p4 sync &&
+		test_path_is_file first-change.t &&
+		echo "cli_file" >cli_file.t &&
+		p4 add cli_file.t &&
+		p4 submit -d "cli change"
+	) &&
+	(git --git-dir "$git" p4 sync) &&
+	(cd "$git" && git checkout -q p4/master) &&
+	test_path_is_file "$git"/cli_file.t &&
+	(
+		cd "$cli" &&
+		echo "cli_file2" >cli_file2.t &&
+		p4 add cli_file2.t  &&
+		p4 submit -d "cli change2"
+	) &&
+	(GIT_DIR="$git" git p4 sync) &&
+	(cd "$git" && git checkout -q p4/master) &&
+	test_path_is_file "$git"/cli_file2.t
+'
+
+
 test_expect_success 'kill p4d' '
 	kill_p4d
 '