Implement 'image' volume type for services

newsfragments/mount-image-as-volume.feature

@@ -0,0 +1 @@
+Support volume.type=image in services, for mounting files from container images.

podman_compose.py

@@ -480,13 +480,20 @@ def mount_desc_to_mount_args(mount_desc: dict[str, Any]) -> str:
         selinux = bind_opts.get("selinux")
         if selinux is not None:
             opts.append(selinux)
+    if mount_type == "image":
+        image_opts = mount_desc.get("image", {})
+        subpath = image_opts.get("subpath")
+        if subpath is not None:
+            opts.append(f"subpath={subpath}")
     opts_str = ",".join(opts)
     if mount_type == "bind":
         return f"type=bind,source={source},destination={target},{opts_str}".rstrip(",")
     if mount_type == "volume":
         return f"type=volume,source={source},destination={target},{opts_str}".rstrip(",")
     if mount_type == "tmpfs":
         return f"type=tmpfs,destination={target},{opts_str}".rstrip(",")
+    if mount_type == "image":
+        return f"type=image,source={source},destination={target},{opts_str}".rstrip(",")
     raise ValueError("unknown mount type:" + mount_type)
 
 
@@ -574,7 +581,7 @@ async def get_mount_args(
     srv_name = cnt["_service"]
     mount_type = volume["type"]
     await assert_volume(compose, volume)
-    if compose.prefer_volume_over_mount:
+    if compose.prefer_volume_over_mount and mount_type != "image":
         if mount_type == "tmpfs":
             # TODO: --tmpfs /tmp:rw,size=787448k,mode=1777
             args = volume["target"]

tests/unit/test_container_to_args.py

@@ -680,6 +680,47 @@ async def test_volumes_bind_mount_source(
             ],
         )
 
+    @parameterized.expand([
+        (
+            "without_subpath",
+            {},
+            "type=image,source=example:latest,destination=/mnt/example",
+        ),
+        (
+            "with_subpath",
+            {"image": {"subpath": "path/to/image/folder"}},
+            "type=image,source=example:latest,destination=/mnt/example,subpath=path/to/image/folder",
+        ),
+    ])
+    async def test_volumes_image_mount(
+        self, test_name: str, image_opts: dict, expected_mount_arg: str
+    ) -> None:
+        c = create_compose_mock()
+        cnt = get_minimal_container()
+        cnt["_service"] = cnt["service_name"]
+
+        cnt["volumes"] = [
+            {
+                "type": "image",
+                "source": "example:latest",
+                "target": "/mnt/example",
+                **image_opts,
+            },
+        ]
+
+        args = await container_to_args(c, cnt)
+        self.assertEqual(
+            args,
+            [
+                "--name=project_name_service_name1",
+                "-d",
+                "--mount",
+                expected_mount_arg,
+                "--network=bridge:alias=service_name",
+                "busybox",
+            ],
+        )
+
     @parameterized.expand([
         (
             "create_host_path_set_to_true",