git am error: “patch does not apply”

Question

I am trying to move several commits from one project to the second, similar one, using git.

So I created a patch, containing 5 commits:

git format-patc         


        

Answer 1

What is a patch?

A patch is little more (see below) than a series of instructions: "add this here", "remove that there", "change this third thing to a fourth". That's why git tells you:

The copy of the patch that failed is found in:
c:/.../project2/.git/rebase-apply/patch

You can open that patch in your favorite viewer or editor, open the files-to-be-changed in your favorite editor, and "hand apply" the patch, using what you know (and git does not) to figure out how "add this here" is to be done when the files-to-be-changed now look little or nothing like what they did when they were changed earlier, with those changes delivered to you as a patch.

A little more

A three-way merge introduces that "little more" information than the plain "series of instructions": it tells you what the original version of the file was as well. If your repository has the original version, your git can compare what you did to a file, to what the patch says to do to the file.

As you saw above, if you request the three-way merge, git can't find the "original version" in the other repository, so it can't even attempt the three-way merge. As a result you get no conflict markers, and you must do the patch-application by hand.

Using --reject

When you have to apply the patch by hand, it's still possible that git can apply most of the patch for you automatically and leave only a few pieces to the entity with the ability to reason about the code (or whatever it is that needs patching). Adding --reject tells git to do that, and leave the "inapplicable" parts of the patch in rejection files. If you use this option, you must still hand-apply each failing patch, and figure out what to do with the rejected portions.

Once you have made the required changes, you can git add the modified files and use git am --continue to tell git to commit the changes and move on to the next patch.

What if there's nothing to do?

Since we don't have your code, I can't tell if this is the case, but sometimes, you wind up with one of the patches saying things that amount to, e.g., "fix the spelling of a word on line 42" when the spelling there was already fixed.

In this particular case, you, having looked at the patch and the current code, should say to yourself: "aha, this patch should just be skipped entirely!" That's when you use the other advice git already printed:

If you prefer to skip this patch, run "git am --skip" instead.

If you run git am --skip, git will skip over that patch, so that if there were five patches in the mailbox, it will end up adding just four commits, instead of five (or three instead of five if you skip twice, and so on).