`git diff` after `git checkout from-branch -- files` reports nothing

[Noel Yap <noel.yap@gmail.com>]

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)

`git checkout -b to-branch; git checkout from-branch -- filenames; git
status; git diff`

What did you expect to happen? (Expected behavior)

`git status` expected to show updated files and `git diff` expected to
show file changes.

What happened instead? (Actual behavior)

`git status` showed updated files but `git diff` showed no file changes.

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

`git diff` was expected to show file changes but it showed nothing instead.

Anything else you want to add:

If I `git reset -q HEAD -- filenames`, `git diff` starts showing file changes.

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 2.34.1
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Linux 5.11.0-36-generic #40~20.04.1-Ubuntu SMP Sat Sep 18
02:14:19 UTC 2021 x86_64
compiler info: gnuc: 9.3
libc info: glibc: 2.31
$SHELL (typically, interactive shell): /bin/bash


[Enabled Hooks]
applypatch-msg
commit-msg
post-applypatch
post-checkout
post-commit
post-merge
post-receive
post-rewrite
post-update
pre-applypatch
pre-auto-gc
pre-commit
pre-merge-commit
pre-push
pre-rebase
pre-receive
prepare-commit-msg
push-to-checkout
sendemail-validate
update