Track dependency conditions when parsing cnditional depends_on

This commit changes the way that depends_on blocks are parsed and
tracked during the `podman-compose up` process.

Each service's dependencies will be tracked as a dict in which keys are
services being depended on and values are the condition to be met by
said services before the current service can start.

This lays the groundwork for supporting long-syntax / conditional
depends_on blocks, but should not change any behavior so far.

Signed-off-by: Adrian Torres <atorresj@redhat.com>

Author: Elkasitu

podman_compose.py

@@ -102,6 +102,27 @@ def strverscmp_lt(a, b):
     return a_ls < b_ls
 
 
+class DependsCondition:  # pylint: disable=too-few-public-methods
+    # enum for possible types of depends_on conditions
+    # see https://github.com/compose-spec/compose-spec/blob/master/spec.md#long-syntax-1
+    STARTED = 0
+    HEALTHY = 1
+    COMPLETED = 2
+
+    @classmethod
+    def to_enum(cls, condition):
+        """
+        Converts and returns a condition value into a valid enum value.
+        """
+        if condition == "service_healthy":
+            return cls.HEALTHY
+        if condition == "service_completed_successfully":
+            return cls.COMPLETED
+        # use cls.STARTED as a catch-all value even
+        # if the condition value is not within spec
+        return cls.STARTED
+
+
 def parse_short_mount(mount_str, basedir):
     mount_a = mount_str.split(":")
     mount_opt_dict = {}
@@ -987,25 +1008,46 @@ def flat_deps(services, with_extends=False):
     create dependencies "_deps" or update it recursively for all services
     """
     for name, srv in services.items():
-        deps = set()
-        srv["_deps"] = deps
+        deps = {}
         if with_extends:
             ext = srv.get("extends", {}).get("service", None)
             if ext:
                 if ext != name:
-                    deps.add(ext)
+                    deps[ext] = DependsCondition.STARTED
                 continue
+        # NOTE: important that the get call is kept as-is, since depends_on
+        # can be an empty string and in that case we want to have an empty list
         deps_ls = srv.get("depends_on", None) or []
         if is_str(deps_ls):
-            deps_ls = [deps_ls]
+            # depends_on: "foo"
+            # treat as condition: service_started
+            deps_ls = {deps_ls: DependsCondition.STARTED}
         elif is_dict(deps_ls):
-            deps_ls = list(deps_ls.keys())
-        deps.update(deps_ls)
+            # depends_on:
+            #   foo:
+            #       condition: service_xxx
+            tmp = {}
+            for service, condition in deps_ls.items():
+                condition = DependsCondition.to_enum(condition.get("condition"))
+                tmp[service] = condition
+            deps_ls = tmp
+        else:
+            # depends_on:
+            # - foo
+            # treat as condition: service_started
+            deps_ls = {dep: DependsCondition.STARTED for dep in deps_ls}
+        deps = {**deps, **deps_ls}
         # parse link to get service name and remove alias
+        # NOTE: important that the get call is kept as-is, since links can
+        # be an empty string and in that case we want to have an empty list
         links_ls = srv.get("links", None) or []
         if not is_list(links_ls):
             links_ls = [links_ls]
-        deps.update([(c.split(":")[0] if ":" in c else c) for c in links_ls])
+        deps = {
+            **deps,
+            **{c.split(":")[0]: DependsCondition.STARTED for c in links_ls},
+        }
+        srv["_deps"] = deps
     for name, srv in services.items():
         rec_deps(services, name)
 
@@ -1922,7 +1964,7 @@ def get_excluded(compose, args):
     if args.services:
         excluded = set(compose.services)
         for service in args.services:
-            excluded -= compose.services[service]["_deps"]
+            excluded -= set(compose.services[service]["_deps"].keys())
             excluded.discard(service)
     log("** excluding: ", excluded)
     return excluded

pytests/test_dependencies.py

@@ -0,0 +1,37 @@
+import pytest
+
+from podman_compose import flat_deps, DependsCondition
+
+
+@pytest.fixture
+def basic_services():
+    return {
+        "foo": {},
+        "bar": {
+            # string dependency
+            "depends_on": "foo",
+        },
+        "baz": {
+            # list dependency
+            "depends_on": ["bar"],
+        },
+        "ham": {
+            # dict / conditional dependency
+            "depends_on": {
+                "foo": {
+                    "condition": "service_healthy",
+                },
+            },
+        },
+    }
+
+
+def test_flat_deps(basic_services):
+    flat_deps(basic_services)
+    assert basic_services["foo"]["_deps"] == {}
+    assert basic_services["bar"]["_deps"] == {"foo": DependsCondition.STARTED}
+    assert basic_services["baz"]["_deps"] == {
+        "bar": DependsCondition.STARTED,
+        "foo": DependsCondition.STARTED,
+    }
+    assert basic_services["ham"]["_deps"] == {"foo": DependsCondition.HEALTHY}

tests/deps/docker-compose.yaml

@@ -21,4 +21,26 @@ services:
       tmpfs:
         - /run
         - /tmp
-
+    hello_world:
+      image: busybox
+      command: ["/bin/busybox", "sh", "-c", "echo 'hello world'"]
+      depends_on:
+        sleep:
+          condition: service_started
+      tmpfs:
+        - /run
+        - /tmp
+      healthcheck:
+        test: echo "hello world"
+        interval: 10s
+        timeout: 5s
+        retries: 5
+    hello_world_2:
+      image: busybox
+      command: ["/bin/busybox", "sh", "-c", "echo 'hello world'"]
+      depends_on:
+        sleep:
+          condition: service_healthy
+      tmpfs:
+        - /run
+        - /tmp