docker compose gives "exited with code 0" while docker run works - docker

Question

Let's say, I have this easy docker-compose.yml:
services:
foo:
container_name: bar
build: .
for the sake of completeness, I also want to share that simple Dockerfile:
FROM ubuntu:20.04
My folder structure is
temp
|- docker-compose.yml
|- Dockerfile
When I build the container with docker compose build, it gives no errors:
[+] Building 0.1s (5/5) FINISHED
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 31B 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/ubuntu:20.04 0.0s
=> CACHED [1/1] FROM docker.io/library/ubuntu:20.04 0.0s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:87da********************************************************bb35 0.0s
=> => naming to docker.io/library/temp-foo 0.0s
Use 'docker scan' to run Snyk tests against images to find vulnerabilities and learn how to fix them
The outpot of that is identical to docker build . -t foo. When I run it with docker run -dt --name bar foo.
When I now issue docker compose up, I get bar exited with code 0:
[+] Running 2/2
- Network temp_default Created 0.0s
- Container bar Created 1.9s
Attaching to bar
bar exited with code 0
How is this possible or even make sense. Shouldn't both fail or work?
I can share the Dockerfile if needed, it's close to that one.