Hi,

I guess this will be hard to fix correctly, but please comment if I've
overlooked something:

1) update foo git repository with new commit ABCD, but forget to push it
2) bump SRCREV in foo.bb to ABCD
3) run bitbake foo, it will run do_fetch to catch new changes in remote
   repo, but ABCD is not there, so do_unpack will fail like this:

   NOTE: Running task 2289 of 4227 (ID: 1185, foo.bb, do_unpack)
   NOTE: recipe foo-1.0+gitr2+ABCD: task do_unpack: Started
   ERROR: Function failed: Fetcher failure: Fetch command failed with exit code 128, output:
   fatal: reference is not a tree: ABCD

4) realize missing "git push" in step 1) and push it now
5) run bitbake foo again, but do_unpack is still failing, because
   do_fetch checksums is the same (nothing changed in metadata) so stamp
   is still valid.

6) fix it with "bitbake -c fetch -f foo", but that could be complicated
   if bump SRCREV was pushed already and possibly many builders already
   executed do_fetch, so maybe push PR bump or something like that.

Only better solution than 6) I can think of, is to detect 
"fatal: reference is not a tree" in do_unpack and if it's git repository
then remove do_fetch stamp and hope it was fixed in remote git repo.

-- 
Martin 'JaMa' Jansa     jabber: Martin.Jansa@gmail.com