Simplify checkup for already existing revision

slapos/recipe/gitclone.py

@@ -282,12 +282,19 @@ class Recipe(object):
       # first cleanup pyc files
       self.deletePycFiles(self.location)
 
+      # Check if the revision exists in the already fetched repository
+      revision_exists = False
+      if self.revision:
+        try:
+          revision_exists = (check_output([self.git_command, 'cat-file', '-t',
+                      self.revision]).strip() == 'commit')
+        except CalledProcessError:
+          print('Revision %s does not exits in the repository' % self.revision)
+          pass
+
       # then update,
       # but, to save time, only if we don't have the revision already
-      revision_already_fetched = \
-            self.revision and   \
-            check_output([self.git_command, 'rev-parse', 'HEAD'],
-                          cwd=self.location).strip() == self.revision
+      revision_already_fetched = self.revision and revision_exists
 
       if not revision_already_fetched:
         check_call([self.git_command, 'fetch', '--all'], cwd=self.location)
@@ -300,9 +307,9 @@ class Recipe(object):
         else:
           self.gitReset('@{upstream}')
 
-      if not revision_already_fetched and not self.ignore_cloning_submodules:
-        # Also update the submodule directory to the commit which parent
-        # repository is pointing to.
+      if not self.ignore_cloning_submodules and self.revision:
+        # Update the submodule to the commit which parent repo points to if
+        # there has been revision is present for the parent repo.
         # According to man-page of submodule, update also clones missing
         # submodules and updating the working tree of the submodules. This is
         # why we do update here only after we are ok with revision of parent