Use origin/ref for all refs other than the system branch ref itself

The rationale here is that inside a checkout of a system branch, the
user should only be committing to the refs for that system branch,
because those are the only ones that 'morph merge' will look at.

This removes a problem where we could be confused by a ref with a
name that would be sorted before 'master' in the result of 'git
show-ref'.

2 files changed, 19 insertions, 6 deletions

diff --git a/morphlib/git.py b/morphlib/git.py
index 27f22351..b3dd2c45 100644
--- a/morphlib/git.py
+++ b/morphlib/git.py
@@ -221,13 +221,12 @@ def clone_into(runcmd, srcpath, targetpath, ref=None):
     else:
         runcmd(['git', 'clone', '-b', ref, srcpath, targetpath])
 
-def find_first_ref(runcmd, gitdir, ref):
-    '''Find the *first* ref match and returns its sha1.'''
-    return runcmd(['git', 'show-ref', ref],
-                  cwd=gitdir).split("\n")[0].split(" ")[0]
-
 def is_valid_sha1(ref):
     '''Checks whether a string is a valid SHA1.'''
 
     valid_chars = 'abcdefABCDEF0123456789'
     return len(ref) == 40 and all([x in valid_chars for x in ref])
+
+def rev_parse(runcmd, gitdir, ref):
+    '''Find the sha1 for the given ref'''
+    return runcmd(['git', 'rev-parse', ref], cwd=gitdir)[0:40]
diff --git a/morphlib/plugins/branch_and_merge_plugin.py b/morphlib/plugins/branch_and_merge_plugin.py
index 279a9948..6f2e38fc 100644
--- a/morphlib/plugins/branch_and_merge_plugin.py
+++ b/morphlib/plugins/branch_and_merge_plugin.py
@@ -221,12 +221,26 @@ class BranchAndMergePlugin(cliapp.Plugin):
         self.app.runcmd(['git', 'remote', 'update'], cwd=dirname)
 
     def load_morphology(self, repo_dir, name, ref=None):
+        '''Returns a morphology, optionally retrieved from a specific ref
+
+        The repositories that make up a system branch checkout should only
+        have modifications to the ref matching that system branch. Unless 'ref'
+        is a sha1, origin/ref will be used instead to ensure that no local
+        modifications are considered and no local tracking branch needs to be
+        created. Where the ref is that of the system branch, 'None' should be
+        passed because we should load directly from the working tree in this
+        case, honouring any uncommitted changes.
+
+        '''
+
         if ref is None:
             filename = os.path.join(repo_dir, '%s.morph' % name)
             with open(filename) as f:
                 text = f.read()
         else:
-            ref = morphlib.git.find_first_ref(self.app.runcmd, repo_dir, ref)
+            if not morphlib.git.is_valid_sha1(ref):
+                ref = morphlib.git.rev_parse(self.app.runcmd, repo_dir,
+                                             'origin/' + ref)
             try:
                 text = self.app.runcmd(['git', 'cat-file', 'blob',
                                        '%s:%s.morph' % (ref, name)],