project: Fix GetHead to handle detached HEADs

The switch to git rev-parse caused GetHead() to return the literal
string 'HEAD' when in a detached state. This broke repo prune, which
expects a commit SHA.

Bug: 434077990
Change-Id: I80b7d5965749096b59e854f61e913aa74c857b99
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/494401
Reviewed-by: Scott Lee <ddoman@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/project.py b/project.py
index 84a5cdf6..4c699d4b 100644
--- a/project.py
+++ b/project.py
@@ -3835,7 +3835,11 @@ class Project:
         def GetHead(self):
             """Return the ref that HEAD points to."""
             try:
-                return self.rev_parse("--symbolic-full-name", HEAD)
+                symbolic_head = self.rev_parse("--symbolic-full-name", HEAD)
+                if symbolic_head == HEAD:
+                    # Detached HEAD. Return the commit SHA instead.
+                    return self.rev_parse(HEAD)
+                return symbolic_head
             except GitError as e:
                 path = self.GetDotgitPath(subpath=HEAD)
                 raise NoManifestException(path, str(e))