gn build: Use "git rev-parse --git-dir" to discover the path to the .git directory.

[pcc]

Summary

This makes it compatible with worktrees.

[serge-sans-paille]

llvm/utils/gn/build/write_vcsrevision.py

52

For the record, on Python3, subprocess.check_output generates bytes and not str. It seems to be ok as an argument to os.path.isdir, but it requires an extra decode() after the strip()

[pcc]

llvm/utils/gn/build/write_vcsrevision.py

52

I tried the modified script with Python 3 and it appeared to work as is. However, I did notice a difference in behaviour between Python 2 and 3, which I've sent a fix for in D56459.

[thakis]

llvm/utils/gn/build/write_vcsrevision.py

35

should this use exists() too to be consistent with line 38?

[serge-sans-paille]

llvm/utils/gn/build/write_vcsrevision.py

52

great, LGTM then.

[pcc]

llvm/utils/gn/build/write_vcsrevision.py

35

The reason why I switched to exists for .git is that .git can either be a file or a directory (because of worktrees). As far as I know .svn will always be a directory so it seems slightly more correct to use isdir here.

llvm/utils/gn/build/write_vcsrevision.py

 #!/usr/bin/env python
 
 """Gets the current revision and writes it to VCSRevision.h."""
 
 from __future__ import print_function
 
 import argparse
 import os
 import subprocess
 import sys
 
 
 THIS_DIR = os.path.abspath(os.path.dirname(__file__))
 LLVM_DIR = os.path.dirname(os.path.dirname(os.path.dirname(THIS_DIR)))
-MONO_DIR = os.path.dirname(LLVM_DIR)
 
 
 def which(program):
     # distutils.spawn.which() doesn't find .bat files,
     # https://bugs.python.org/issue2200
     for path in os.environ["PATH"].split(os.pathsep):
         candidate = os.path.join(path, program)
         if os.path.isfile(candidate) and os.access(candidate, os.X_OK):
             return candidate
     return None
 
 
 def main():
     parser = argparse.ArgumentParser(description=__doc__)
     parser.add_argument('-d', '--depfile',
                         help='if set, writes a depfile that causes this script '
                              'to re-run each time the current revision changes')
     parser.add_argument('vcs_header', help='path to the output file to write')
     args = parser.parse_args()
 
     if os.path.isdir(os.path.join(LLVM_DIR, '.svn')):
         print('SVN support not implemented', file=sys.stderr)
         return 1
-    if os.path.isdir(os.path.join(LLVM_DIR, '.git')):
+    if os.path.exists(os.path.join(LLVM_DIR, '.git')):
         print('non-mono-repo git support not implemented', file=sys.stderr)
         return 1
 
-    git_dir = os.path.join(MONO_DIR, '.git')
-    if not os.path.isdir(git_dir):
-        print('.git dir not found at "%s"' % git_dir, file=sys.stderr)
-        return 1
-
     git, use_shell = which('git'), False
     if not git:
         git = which('git.exe')
     if not git:
         git = which('git.bat')
         use_shell = True
+
+    git_dir = subprocess.check_output([git, 'rev-parse', '--git-dir'],
+                                      cwd=LLVM_DIR, shell=use_shell).strip()
+    if not os.path.isdir(git_dir):
+        print('.git dir not found at "%s"' % git_dir, file=sys.stderr)
+        return 1
+
     rev = subprocess.check_output([git, 'rev-parse', '--short', 'HEAD'],
                                   cwd=git_dir, shell=use_shell)
     # FIXME: add pizzas such as the svn revision read off a git note?
     vcsrevision_contents = '#define LLVM_REVISION "git-%s"\n' % rev.strip()
 
     # If the output already exists and is identical to what we'd write,
     # return to not perturb the existing file's timestamp.
     if os.path.exists(args.vcs_header) and \