pytorch

f36345eb - improve error message on incorrect inputs into gather for (#27439)

improve error message on incorrect inputs into gather for (#27439) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/27439 When users call dist.gather, they have to pass in a `gather_list` to the function on the destination worker, and this list needs to have the same size as the number of processes in the group. When the user initializes this list incorrectly, the current error message is not very helpful: This changes the error message so that the incorrect gather_list size is pointed out and the correct one is given. ghstack-source-id: 91413442 Test Plan: Added a unit test and tested with an incorrect gather_list size. Differential Revision: D17781370 fbshipit-source-id: b49aad1b1197daf77daa10911296664e6340e2fa