git-apply fails mysteriously, how do I troubleshoot/fix?

Question

I\'m currently trying to to code-style checking on the PRs of a (github) repository, and I want to deliver patches to the submitters with which they can easily fix the codes

Answer 1

Update:

You can use git apply -v to see more detailed info about what's going on, git apply --check to just verify the operation, or git apply --index to rebuild the local index file.

Based on your comment, it seems your local index was corrupted, and so index solved it.

I will leave my original answer and the comments mostly to give people context on what was going on, as I suspect other people would jump to the same initial conclusions I had based on the problem description.

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Most likely nothing's wrong with the diff. Instead look at the target git repository. While you are doing git reset --hard HEAD, nothing guarantees you that the HEAD on that other repository is the same as the HEAD on your.

Do git log on the target repo and look at the commit at the top. Is it the same as the one you produced the diff from? Most likely it is not. Look down the history and check if the commit you need is there. If it is, then the target repo is ahead of yours, and you have to go back, do git pull (or git rebase) and produce a new diff. If it isn't, then the target repo is behind yours, and you need to do git pull (or git rebase) on the target repo to bring it up to speed.

Keep in mind that if you have other people committing to your "master" repo (the one where bot yours and the target repositories are pulling from), you might have to git pull both repositories, to get them to a reasonably recent common commit.