Support variable substitution with service's environment

This commit introduces the ability to substitute environment variables
within the 'environment' section of the service definition.

This allows for more dynamic configuration of services.

Signed-off-by: Songmin Li <lisongmin@protonmail.com>

Author: lisongmin

newsfragments/substitution-with-service-environment.feature

@@ -0,0 +1 @@
+Add ability to substitute variables with the environment of the service.

podman_compose.py

@@ -264,6 +264,16 @@ def rec_subs(value, subs_dict):
     do bash-like substitution in value and if list of dictionary do that recursively
     """
     if is_dict(value):
+        if 'environment' in value and is_dict(value['environment']):
+            # Load service's environment variables
+            subs_dict = subs_dict.copy()
+            svc_envs = {k: v for k, v in value['environment'].items() if k not in subs_dict}
+            # we need to add `svc_envs` to the `subs_dict` so that it can evaluate the
+            # service environment that reference to another service environment.
+            subs_dict.update(svc_envs)
+            svc_envs = rec_subs(svc_envs, subs_dict)
+            subs_dict.update(svc_envs)
+
         value = {k: rec_subs(v, subs_dict) for k, v in value.items()}
     elif is_str(value):
 
@@ -1823,6 +1833,11 @@ def _parse_compose_file(self):
             "COMPOSE_FILE": pathsep.join(relative_files),
             "COMPOSE_PATH_SEPARATOR": pathsep,
         })
+
+        if args and 'env' in args and args.env:
+            env_vars = norm_as_dict(args.env)
+            self.environ.update(env_vars)
+
         compose = {}
         # Iterate over files primitively to allow appending to files in-loop
         files_iter = iter(files)

tests/integration/env-tests/container-compose.yml

@@ -1,9 +1,10 @@
-version: '3'
+version: "3"
 
 services:
   env-test:
     image: busybox
     command: sh -c "export | grep ZZ"
     environment:
-    - ZZVAR1=myval1
-
+      ZZVAR1: myval1
+      ZZVAR2: 2-$ZZVAR1
+      ZZVAR3: 3-$ZZVAR2