Bug report: git apply --cached --reject

Hi,

Below the fold is a `git bugreport`-generated report of a bug with `git apply --cached --reject`, which I have reproduced in three different environments. Summary: we do not correctly stage the removal of a file if there is also an unrelated change that cannot be applied.

I don't think this behaviour is intended; in the report I give a couple of variations which correctly do what I expected, and this one breaks the semantics I expect, given the behaviour of those variations. I have not tried to find the source of the bug.

Thanks, Patrick Stevens

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Thank you for filling out a Git bug report! Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)

Complete reproduction instructions:

``` mkdir badrepo && cd badrepo && git init echo "start" >> file.txt && git add file.txt && git commit -m "Initial commit" git tag initialcommit echo "another" >> another.txt && git add another.txt && git commit -m "Something else" git tag commit2 git rm another.txt && git rm file.txt && git commit -m "Remove both" git tag commit3 git checkout initialcommit git diff commit2 commit3 | git apply --reject --cached ```

What did you expect to happen? (Expected behavior)

We should be left detached at tag `initialcommit`, with the working copy clean (i.e. containing only `file.txt`), and with the deletion of `file.txt` staged.

What happened instead? (Actual behavior)

The final `git apply` correctly leaves us detached at tag `initialcommit`, with a clean working copy, but incorrectly the deletion of `file.txt` is not staged: the index is also clean.

What's different between what you expected and what actually happened?

The file `file.txt` should have had its deletion staged, because this is part of the diff which could apply cleanly.

Anything else you want to add:

If I delete the `--cached` from the last line, the right thing happens: the working copy has `file.txt` deleted in the working copy but the deletion is not staged. If instead I remove the `git rm another.txt`, then similarly the right thing happens: now we end up with the deletion of `file.txt` staged (but the working copy is correctly unchanged).

I have reproduced this using git version 2.24.1.windows.2, as well as 2.29.2 built on Windows using the WSL and invoked through WSL, as well as from the Mac HomeBrew install where I produced this bug report.

Please review the rest of the bug report below. You can delete any lines you don't wish to share.

[System Info] git version: git version 2.29.2 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Darwin 18.7.0 Darwin Kernel Version 18.7.0: Mon Aug 31 20:53:32 PDT 2020; root:xnu-4903.278.44~1/RELEASE_X86_64 x86_64 compiler info: clang: 11.0.0 (clang-1100.0.33.17) libc info: no libc information available $SHELL (typically, interactive shell): /bin/zsh

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