fix: podman-compose down should not stop the upstream dependencies.

Say there is an app service depends on a db service,
when we run `podman-compose down app`, the db service should not be stopped.

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

newsfragments/fix-stop-wrong-dependents-on-compose-down.bugfix

@@ -0,0 +1 @@
+Fix `podman-compose down service` stops wrong dependents

podman_compose.py

@@ -1433,6 +1433,16 @@ def rec_deps(
     return deps
 
 
+def calc_dependents(services: dict[str, Any]) -> None:
+    for name, srv in services.items():
+        deps: set[ServiceDependency] = srv.get("_deps", set())
+        for dep in deps:
+            if dep.name in services:
+                services[dep.name].setdefault("_dependents", set()).add(
+                    ServiceDependency(name, dep.condition.value)
+                )
+
+
 def flat_deps(services: dict[str, Any], with_extends: bool = False) -> None:
     """
     create dependencies "_deps" or update it recursively for all services
@@ -1470,6 +1480,8 @@ def flat_deps(services: dict[str, Any], with_extends: bool = False) -> None:
     for name, srv in services.items():
         rec_deps(services, name)
 
+    calc_dependents(services)
+
 
 ###################
 # Override and reset tags
@@ -3028,10 +3040,11 @@ def get_excluded(compose: PodmanCompose, args: argparse.Namespace) -> set[str]:
     excluded = set()
     if args.services:
         excluded = set(compose.services)
+        dep_field = "_dependents" if args.command in ["down"] else "_deps"
         for service in args.services:
             # we need 'getattr' as compose_down_parse dose not configure 'no_deps'
             if service in compose.services and not getattr(args, "no_deps", False):
-                excluded -= set(x.name for x in compose.services[service]["_deps"])
+                excluded -= set(x.name for x in compose.services[service].get(dep_field, set()))
             excluded.discard(service)
     log.debug("** excluding: %s", excluded)
     return excluded

tests/unit/test_depends_on.py

@@ -0,0 +1,53 @@
+import unittest
+from typing import Any
+
+from parameterized import parameterized
+
+from podman_compose import flat_deps
+
+
+class TestDependsOn(unittest.TestCase):
+    @parameterized.expand([
+        (
+            {
+                "service_a": {},
+                "service_b": {"depends_on": {"service_a": {"condition": "healthy"}}},
+                "service_c": {"depends_on": {"service_b": {"condition": "healthy"}}},
+            },
+            # dependencies
+            {
+                "service_a": set(),
+                "service_b": set(["service_a"]),
+                "service_c": set(["service_a", "service_b"]),
+            },
+            # dependents
+            {
+                "service_a": set(["service_b", "service_c"]),
+                "service_b": set(["service_c"]),
+                "service_c": set(),
+            },
+        ),
+    ])
+    def test_flat_deps(
+        self,
+        services: dict[str, Any],
+        deps: dict[str, set[str]],
+        dependents: dict[str, set[str]],
+    ) -> None:
+        flat_deps(services)
+        self.assertEqual(
+            {
+                name: set([x.name for x in value.get("_deps", set())])
+                for name, value in services.items()
+            },
+            deps,
+            msg="Dependencies do not match",
+        )
+        self.assertEqual(
+            {
+                name: set([x.name for x in value.get("_dependents", set())])
+                for name, value in services.items()
+            },
+            dependents,
+            msg="Dependents do not match",
+        )