kargs: interactive changes through editor always result in 'No changes'

[lucab]

Host system details

$ sudo rpm-ostree status
State: idle
AutomaticUpdatesDriver: Zincati
  DriverState: active; periodically polling for updates (last checked Tue 2021-10-19 09:20:33 UTC)
Deployments:
* fedora:fedora/x86_64/coreos/stable
                   Version: 34.20210919.3.0 (2021-10-04T17:11:11Z)
                    Commit: 6334e11901fba7403600522286d817b520eeb15b66b341b392e0c08ed2576b74
              GPGSignature: Valid signature by 8C5BA6990BDB26E19F2A1A801161AE6945719A39

  fedora:fedora/x86_64/coreos/stable
                   Version: 34.20210904.3.0 (2021-09-20T15:25:53Z)
                    Commit: 45e0f7e030762d03f5fb4584463cc0b81a320e641ef5e8403a9651231d2a555b
              GPGSignature: Valid signature by 8C5BA6990BDB26E19F2A1A801161AE6945719A39

$ sudo rpm-ostree --version
rpm-ostree:
 Version: '2021.10'
 Git: 8554a70583a38db5e270978ee153a5ab5a5a4f94
 Features:
  - compose
  - rust
  - fedora-integration

Expected vs actual behavior

Changing kargs through the rpm-ostree spawned editor does not apply the changes.
After tweaking the arguments interactively, it does not detect any change and instead says:

$ sudo rpm-ostree kargs --editor
No changes.

[lucab]

Going a bit back in time, the last version where this seems to work is 2021.4 (on FCOS 34.20210518.3.0), while 2021.5 (on FCOS 34.20210529.3.0) always returns No changes.
So a regression likely got introduced in one of the changes in https://github.com/coreos/rpm-ostree/releases/tag/v2021.5.

[miabbott]

These three PRs stick out from the release notes:

#2713
#2776
#2820

[lucab]

It looks like we do lack e2e tests on this. A quick reproducer that I used to check this is

EDITOR="sed -i 's/$/ foo=bar/'" rpm-ostree kargs --editor