Re: [PATCHv3] 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 <redacted>
---
 git-p4.py                 | 17 +++++++++++++----
 t/t9800-git-p4-basic.sh   | 20 ++++++++++++++++++++
 t/t9806-git-p4-options.sh | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/git-p4.py b/git-p4.py
index fd5ca52..6a1f65f 100755
--- a/git-p4.py
+++ b/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