Always use `git rev-parse --verify` to resolve refs

Previously some code used `git show-ref`, which is wrong -- given two
refs named 'alpha/master' and 'master', `git show-ref master` will
return both, sorted alphabetically. This can lead to build failures,
etc. due to refs resolving to the wrong SHAs.

We should also use `git rev-parse --verify` to verify SHA1s, which
we previously did with `git rev-list`.

Finally, `git rev-parse --verify` is more than twice as fast as
`git show-ref`.

1 files changed, 9 insertions, 20 deletions

diff --git a/morphlib/cachedrepo.py b/morphlib/cachedrepo.py
index 0b5ce60f..312f580f 100644
--- a/morphlib/cachedrepo.py
+++ b/morphlib/cachedrepo.py
@@ -112,18 +112,10 @@ class CachedRepo(object):
 
         '''
 
-        if not morphlib.git.is_valid_sha1(ref):
-            try:
-                refs = self._show_ref(ref).split('\n')
-                refs = [x.split() for x in refs]
-                absref = refs[0][0]
-            except cliapp.AppException:
-                raise InvalidReferenceError(self, ref)
-        else:
-            try:
-                absref = self._rev_list(ref).strip()
-            except cliapp.AppException:
-                raise InvalidReferenceError(self, ref)
+        try:
+            absref = self._rev_parse(ref)
+        except cliapp.AppException:
+            raise InvalidReferenceError(self, ref)
 
         tree = self._show_tree_hash(absref)
         return absref, tree
@@ -141,7 +133,7 @@ class CachedRepo(object):
         if not morphlib.git.is_valid_sha1(ref):
             raise UnresolvedNamedReferenceError(self, ref)
         try:
-            sha1 = self._rev_list(ref).strip()
+            sha1 = self._rev_parse(ref)
         except cliapp.AppException:
             raise InvalidReferenceError(self, ref)
 
@@ -193,7 +185,7 @@ class CachedRepo(object):
         '''Loads a morphology from a given ref'''
 
         if not morphlib.git.is_valid_sha1(ref):
-            ref = self._rev_list(ref).strip()
+            ref = self._rev_parse(ref)
         text = self.cat(ref, '%s.morph' % name)
         morphology = morphlib.morph2.Morphology(text)
         return morphology
@@ -210,7 +202,7 @@ class CachedRepo(object):
         if not morphlib.git.is_valid_sha1(ref):
             raise UnresolvedNamedReferenceError(self, ref)
         try:
-            sha1 = self._rev_list(ref).strip()
+            sha1 = self._rev_parse(ref)
         except cliapp.AppException:
             raise InvalidReferenceError(self, ref)
 
@@ -237,16 +229,13 @@ class CachedRepo(object):
             kwargs['cwd'] = self.path
         return self.app.runcmd(*args, **kwargs)
 
-    def _show_ref(self, ref):  # pragma: no cover
-        return self._runcmd(['git', 'show-ref', ref])
+    def _rev_parse(self, ref):  # pragma: no cover
+        return self._runcmd(['git', 'rev-parse', '--verify', ref])[0:40]
 
     def _show_tree_hash(self, absref):  # pragma: no cover
         return self._runcmd(
                 ['git', 'log', '-1', '--format=format:%T', absref]).strip()
 
-    def _rev_list(self, ref):  # pragma: no cover
-        return self._runcmd(['git', 'rev-list', '--no-walk', ref])
-
     def _ls_tree(self, ref):  # pragma: no cover
         result = self._runcmd(['git', 'ls-tree', '--name-only', ref])
         return result.split('\n')