Don't attempt to load symlinks as morphologies

This was noticed because our definitions.git had a dangling symlink,
so it failed to construct the temporary build branch.

We shouldn't process symlinks as morphologies either, since either we
make symlinked morphologies a first-class behaviour, and validate that
the link points inside the repository, which is a lot of work for
something we don't and probably won't need; or we can just assume that
we deal with the morphology this is linked to correctly anyway.

1 files changed, 10 insertions, 0 deletions

diff --git a/morphlib/gitdir.py b/morphlib/gitdir.py
index 8f6d69d7..5b0693cb 100644
--- a/morphlib/gitdir.py
+++ b/morphlib/gitdir.py
@@ -515,6 +515,16 @@ class GitDirectory(object):
         tree = self.resolve_ref_to_tree(ref)
         return self.get_file_from_ref(tree, filename)
 
+    def is_symlink(self, filename, ref=None):
+        if ref is None and self.is_bare():
+            raise NoWorkingTreeError(self)
+        if ref is None:
+            filepath = os.path.join(self.dirname, filename.lstrip('/'))
+            return os.path.islink(filepath)
+        tree_entry = self._runcmd(['git', 'ls-tree', ref, filename])
+        file_mode = tree_entry.split(' ', 1)[0]
+        return file_mode == '120000'
+
     @property
     def HEAD(self):
         output = self._runcmd(['git', 'rev-parse', '--abbrev-ref', 'HEAD'])