Add option to correct gitdir when syncing

In some cases, a user may wish to continue with a sync even though
it would require overwriting an existing git directory. This behavior
is not safe as a default because it could result in the loss of some
user data, but as an optional flag it allows the user more flexibility.

To support this, add a --force-sync flag to the sync command that will
attempt to overwrite the existing git dir if it is specified and the
existing git dir points to the wrong obj dir.

Change-Id: Ieddda8ad54e264a1eb4a9d54881dd6ebc8a03833

2 files changed, 46 insertions, 11 deletions

diff --git a/project.py b/project.py
index 9e8ee86..868425c 100644
--- a/project.py
+++ b/project.py
@@ -32,7 +32,7 @@ import traceback
 from color import Coloring
 from git_command import GitCommand, git_require
 from git_config import GitConfig, IsId, GetSchemeFromUrl, ID_RE
-from error import GitError, HookError, UploadError
+from error import GitError, HookError, UploadError, DownloadError
 from error import ManifestInvalidRevisionError
 from error import NoManifestException
 from trace import IsTrace, Trace
@@ -1101,6 +1101,7 @@ class Project(object):
       quiet=False,
       is_new=None,
       current_branch_only=False,
+      force_sync=False,
       clone_bundle=True,
       no_tags=False,
       archive=False,
@@ -1140,7 +1141,7 @@ class Project(object):
     if is_new is None:
       is_new = not self.Exists
     if is_new:
-      self._InitGitDir()
+      self._InitGitDir(force_sync=force_sync)
     else:
       self._UpdateHooks()
     self._InitRemote()
@@ -1233,11 +1234,11 @@ class Project(object):
         'revision %s in %s not found' % (self.revisionExpr,
                                          self.name))
 
-  def Sync_LocalHalf(self, syncbuf):
+  def Sync_LocalHalf(self, syncbuf, force_sync=False):
     """Perform only the local IO portion of the sync process.
        Network access is not required.
     """
-    self._InitWorkTree()
+    self._InitWorkTree(force_sync=force_sync)
     all_refs = self.bare_ref.all
     self.CleanPublishedCache(all_refs)
     revid = self.GetRevisionId(all_refs)
@@ -2164,7 +2165,7 @@ class Project(object):
     if GitCommand(self, cmd).Wait() != 0:
       raise GitError('%s merge %s ' % (self.name, head))
 
-  def _InitGitDir(self, mirror_git=None):
+  def _InitGitDir(self, mirror_git=None, force_sync=False):
     init_git_dir = not os.path.exists(self.gitdir)
     init_obj_dir = not os.path.exists(self.objdir)
     try:
@@ -2181,7 +2182,20 @@ class Project(object):
         if init_obj_dir or init_git_dir:
           self._ReferenceGitDir(self.objdir, self.gitdir, share_refs=False,
                                 copy_all=True)
-        self._CheckDirReference(self.objdir, self.gitdir, share_refs=False)
+        try:
+          self._CheckDirReference(self.objdir, self.gitdir, share_refs=False)
+        except GitError as e:
+          print("Retrying clone after deleting %s" % force_sync, file=sys.stderr)
+          if force_sync:
+            try:
+              shutil.rmtree(os.path.realpath(self.gitdir))
+              if self.worktree and os.path.exists(
+                  os.path.realpath(self.worktree)):
+                shutil.rmtree(os.path.realpath(self.worktree))
+              return self._InitGitDir(mirror_git=mirror_git, force_sync=False)
+            except:
+              raise e
+          raise e
 
       if init_git_dir:
         mp = self.manifest.manifestProject
@@ -2308,7 +2322,8 @@ class Project(object):
         src = os.path.realpath(os.path.join(srcdir, name))
         # Fail if the links are pointing to the wrong place
         if src != dst:
-          raise GitError('cannot overwrite a local work tree')
+          raise GitError('--force-sync not enabled; cannot overwrite a local '
+                         'work tree')
 
   def _ReferenceGitDir(self, gitdir, dotgit, share_refs, copy_all):
     """Update |dotgit| to reference |gitdir|, using symlinks where possible.
@@ -2361,11 +2376,11 @@ class Project(object):
             shutil.copy(src, dst)
       except OSError as e:
         if e.errno == errno.EPERM:
-          raise GitError('filesystem must support symlinks')
+          raise DownloadError('filesystem must support symlinks')
         else:
           raise
 
-  def _InitWorkTree(self):
+  def _InitWorkTree(self, force_sync=False):
     dotgit = os.path.join(self.worktree, '.git')
     init_dotgit = not os.path.exists(dotgit)
     try:
@@ -2374,7 +2389,16 @@ class Project(object):
         self._ReferenceGitDir(self.gitdir, dotgit, share_refs=True,
                               copy_all=False)
 
-      self._CheckDirReference(self.gitdir, dotgit, share_refs=True)
+      try:
+        self._CheckDirReference(self.gitdir, dotgit, share_refs=True)
+      except GitError as e:
+        if force_sync:
+          try:
+            shutil.rmtree(dotgit)
+            return self._InitWorkTree(force_sync=False)
+          except:
+            raise e
+        raise e
 
       if init_dotgit:
         _lwrite(os.path.join(dotgit, HEAD), '%s\n' % self.GetRevisionId())
diff --git a/subcmds/sync.py b/subcmds/sync.py
index ec333ae..a8074a4 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -119,6 +119,11 @@ credentials.
 The -f/--force-broken option can be used to proceed with syncing
 other projects if a project sync fails.
 
+The --force-sync option can be used to overwrite existing git
+directories if they have previously been linked to a different
+object direcotry. WARNING: This may cause data to be lost since
+refs may be removed when overwriting.
+
 The --no-clone-bundle option disables any attempt to use
 $URL/clone.bundle to bootstrap a new Git repository from a
 resumeable bundle file on a content delivery network. This
@@ -174,6 +179,11 @@ later is required to fix a server side protocol bug.
     p.add_option('-f', '--force-broken',
                  dest='force_broken', action='store_true',
                  help="continue sync even if a project fails to sync")
+    p.add_option('--force-sync',
+                 dest='force_sync', action='store_true',
+                 help="overwrite an existing git directory if it needs to "
+                      "point to a different object directory. WARNING: this "
+                      "may cause loss of data")
     p.add_option('-l', '--local-only',
                  dest='local_only', action='store_true',
                  help="only update working tree, don't fetch")
@@ -281,6 +291,7 @@ later is required to fix a server side protocol bug.
         success = project.Sync_NetworkHalf(
           quiet=opt.quiet,
           current_branch_only=opt.current_branch_only,
+          force_sync=opt.force_sync,
           clone_bundle=not opt.no_clone_bundle,
           no_tags=opt.no_tags, archive=self.manifest.IsArchive,
           optimized_fetch=opt.optimized_fetch)
@@ -696,7 +707,7 @@ later is required to fix a server side protocol bug.
     for project in all_projects:
       pm.update()
       if project.worktree:
-        project.Sync_LocalHalf(syncbuf)
+        project.Sync_LocalHalf(syncbuf, force_sync=opt.force_sync)
     pm.end()
     print(file=sys.stderr)
     if not syncbuf.Finish():