[Defect] process-compose project update can't update when processes is empty list

[misuzu]

Defect

Make sure that these boxes are checked before submitting your issue -- thank you!

• Included the relevant configuration snippet
• Included the relevant process-compose log (log location: process-compose info)
• Included a [Minimal, Complete, and Verifiable example] (https://stackoverflow.com/help/mcve)

Version of process-compose: v1.40.1

OS environment: NixOS unstable

Steps or code to reproduce the issue:

1. create two configs:

cat <<'EOF' > /tmp/test-config-0.yaml
version: "0.5"

processes:
EOF
cat <<'EOF' > /tmp/test-config-1.yaml
version: "0.5"

processes:
  hello:
    command: echo 'Hello World'
  pc:
    command: echo 'From Process Compose'
    depends_on:
      hello:
        condition: process_completed
EOF

2. run process-compose with the first config

process-compose up --keep-project -f /tmp/test-config-0.yaml

3. update running process-compose instance using the second config

process-compose project update -f /tmp/test-config-1.yaml

Expected result:

The hello and pc appear in the TUI, the project update exits without errors.

Actual result:

The TUI shows panics for a short time and the project update command exits with an error:

% process-compose project update -f /tmp/test-config-1.yaml
24-12-10 20:55:00.271 FTL Failed to update project error=EOF
% cat /tmp/process-compose-misuzu.log
24-12-10 20:54:55.068 INF Process Compose v1.40.1
24-12-10 20:54:55.068 INF Loaded project from /tmp/test-config-0.yaml
24-12-10 20:54:55.068 INF Global shell command: bash -c
24-12-10 20:54:55.069 INF start http server listening :8080
24-12-10 20:54:55.069 DBG Spinning up 0 processes. Order: []
24-12-10 20:54:55.069 INF Project completed
24-12-10 20:55:00.270 DBG Process hello is new
24-12-10 20:55:00.270 DBG Process pc is new

When starting with /tmp/test-config-1.yaml and updating to /tmp/test-config-0.yaml everything seems to be fine.

[F1bonacc1]

Hey @misuzu,

Thanks for letting me know about this edge case.
I have a fix, but I am not sure it's what you expect.
Let me explain the issue: When the project is loaded with no processes, the processes value is Nil.
When adding new processes to a Nil value, PC fails.
There are 2 possible fixes:

1. Initialize the value to be an empty map of processes.
2. Fail the start of process compose - 0 processes is probably not what the user intended to start and should be warned.

Currently, I am leaning toward option 2 and would've liked to hear your opinion before delivering a fix that might not match your use case.

[misuzu]

I see, this is actually another yaml gotcha. The processes: means {"processes": null}. For some reason I've expected it to be {"processes": {}}.
With this config everything seems to work as expected:

version: "0.5"

processes: {}

The plan was to start an empty process-compose instance in a systemd unit and then use project update to deploy stuff to it.
I think the first fix would be better and less confusing than how it works now.
With the second one I'd need to add some "default" process just to satisfy the 0 process check, which would be weird...

[F1bonacc1]

If your use case is to support an empty process list, I can fail in case of:

version: "0.5"
processes:

And let it run in case of:

version: "0.5"
processes: {}

WDYT?

[misuzu]

WDYT?

From the user's point of view, both configurations have empty processes. I would follow the principle of least surprise and make both configurations equivalent

[F1bonacc1]

Fixed in v1.46.0