What to do if git-am fails with “does not exist in index”?

The patch was not created against the correct source tree.

One way this could happen:

Assume your original branch (the one you want to apply the patch to) has commits:

1. 1a -> 1b -> 1c -> 1d

This branch is then cloned, and new commits are made:

2. 1a -> 1b -> 1c -> 1d -> 1e

Commit 1e included old/filename

Now you do the work in the patch, based on the second branch, not the original one:

3. 1a -> 1b -> 1c -> 1d -> 1e -> 1f

Commit 1f included the rename old/filename -> new/filename

Now, if you create a patch for commit 1f, you won't be able to apply it on top of commit 1d, because commit 1e is missing where old/filename was added to the index/repository.

You can use --reject to get it to do its best and output the rest in .rej files. Then you can fix it up manually and commit.

Tip extracted from: Raymes Khoury.

'git am" does not give very clear location of failure. I did the following:Use "patch -p n patch_file" to try. This unix "patch" command shows clearly where the rejection happens. If patch command works, then the patch file is fine.

I saw "patch -p n" command worked, but "git am -p n" stilled failed with vague and confusing error message "does not exist in index". I suspected it just could not find the right file. So I tweaked n to n-1. Then it worked.

So, the actual cause is that -p arg should be fed with n-1, where n is the right one for the "patch" command.

In short, the working command is "git am -p n-1 patch_file".