The Travis CI config runs the command:

git diff --name-only 49f6449ef4b81537c19b82329caaf60596c516c2...d0c822cded495409b68432fa10f9573417ca1fb7

Git fails with "fatal: Invalid symmetric difference expression (...)" if it doesn't know one or both sha1.

The first problem is that 49f6449ef4b81537c19b82329caaf60596c516c2 is "old" (Date: Sun Jul 16 07:29:16 2017), whereas Travis CI only gets the 50 latest commits:

git clone --depth=50 https://github.com/python/cpython.git python/cpython

I tested: 50 is not enough to get this commit.

haypo@selma$ git clone --depth=50 https://github.com/python/cpython.git python/cpython haypo@selma$ cd python/cpython/ haypo@selma$ git show 49f6449ef4b81537c19b82329caaf60596c516c2 fatal: bad object 49f6449ef4b81537c19b82329caaf60596c516c2

If "git diff" fails, we should simply run all tests.

Victor