sync: Recover from errors during read-tree

When repo is initializing a git repository, it calls `git read-tree`.
During such operation, git is restoring workspace based on the current
index. However, some things can go wrong: a user can run out of disk
space, or, in case of partial clone, user may no longer reach the remote
host. That will leave affected repository in a bad state with partially
checked out workspace. The follow up repo sync won't try to fix such
state.

This change removes .git symlink, which will force the next `repo sync`
to redo Git repository setup.

Bug: b/363171216
Bug: b/390161127
Change-Id: I57db4b6cae0ef21826dc7cede4d3bf02cfc3d955
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/447801
Reviewed-by: Scott Lee <[email protected]>
Tested-by: Josip Sokcevic <[email protected]>
Commit-Queue: Josip Sokcevic <[email protected]>

Author: sokcevicG

project.py

@@ -3443,11 +3443,18 @@ def _InitWorkTree(self, force_sync=False, submodules=False):
 
                 # Finish checking out the worktree.
                 cmd = ["read-tree", "--reset", "-u", "-v", HEAD]
-                if GitCommand(self, cmd).Wait() != 0:
-                    raise GitError(
-                        "Cannot initialize work tree for " + self.name,
-                        project=self.name,
-                    )
+                try:
+                    if GitCommand(self, cmd).Wait() != 0:
+                        raise GitError(
+                            "Cannot initialize work tree for " + self.name,
+                            project=self.name,
+                        )
+                except Exception as e:
+                    # Something went wrong with read-tree (perhaps fetching
+                    # missing blobs), so remove .git to avoid half initialized
+                    # workspace from which repo can't recover on its own.
+                    platform_utils.remove(dotgit)
+                    raise e
 
                 if submodules:
                     self._SyncSubmodules(quiet=True)