Environment variables from env_file containing a "#" are truncated in V2

[ceelian]

Description

Environment variables which contain "#" in the value are truncated starting from the "#" when using the env_file.
For example the line TEST_VAR=abc#def in an env_file will lead to TEST_VAR=abc in the container instead of TEST_VAR=abc#def

Regarding the official docs

Lines beginning with # are treated as comments and are ignored.

only lines beginning with an "#" should be ignored, so the given example should work.

Steps to reproduce the issue:

1. create a env file with a line TEST_VAR=abc#def
2. create a docker compose service which uses the env file
3. connect to a shell inside the container and execute printenv | grep TEST_VAR

Describe the results you received:
TEST_VAR=abc

Describe the results you expected:
TEST_VAR=abc#def

Additional information you deem important (e.g. issue happens only occasionally):
It works on compose 1.29.2 it is not working on 2.3.3

Output of docker compose version:

$ docker compose version  
Docker Compose version v2.3.3

Output of docker info:

docker info           
Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc., v0.8.1)
  compose: Docker Compose (Docker Inc., v2.3.3)
  scan: Docker Scan (Docker Inc., v0.17.0)

Server:
 Containers: 46
  Running: 34
  Paused: 0
  Stopped: 12
 Images: 30
 Server Version: 20.10.13
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 2a1d4dbdb2a1030dc5b01e96fb110a9d9f150ecc
 runc version: v1.0.3-0-gf46b6ba
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
  cgroupns
 Kernel Version: 5.10.104-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: aarch64
 CPUs: 5
 Total Memory: 31.31GiB
 Name: docker-desktop
 ID: EPXM:RZ2P:Q5WT:LTKD:H47P:HYP3:Y762:HODR:NHFO:EJJE:DHMF:ZIJV
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5000
  127.0.0.0/8
 Live Restore Enabled: false

[ulyssessouza]

Actually what's happening is that it's just interpreting it as an inline comment.
To avoid that you can use double quotes to indicate that the "#" makes part of the value and not an inline comment.
That would be like:

TEST_VAR="abc#def"

[ceelian]

@ulyssessouza Agree, but that's not documented. Anyway it is a breaking change from V1 to V2. Do you know if this breaking change is mentioned somewhere?

[ceelian]

IMO this is still an open issue because if this is intended behaviour than the documentation is wrong as mentioned/linked in my first post.

Personally I find that the V1 behaviour which is officially documented and only accepts comments if the first character in a line is "#" makes more sense and is less error prone.

[ulyssessouza]

@ceelian I agree. But at the same time I see that as a nice feature. So I'm proposing a change to the documentation to reflect the new behaviour

docker/docs#14507

[ceelian]

@ulyssessouza Thank you for the quick PR and merge. Don't get me wrong but could you explain why you think the breaking change is a "nice feature"? I mainly see the disadvantage of a breaking change which will cause more work for the DevOps when they want/need to migrate to V2. But maybe I overlook some demanded advantages of the change.

I am just curious I know you already decided and merged the PR.