quadlet: expand %N specifier in the Pod key

docs/source/markdown/podman-container.unit.5.md.in

@@ -273,6 +273,11 @@ setting up a container healthcheck, see the `HealthCmd` option for more.
 Specify a Quadlet `.pod` unit to link the container to.
 The value must take the form of `<name>.pod` and the `.pod` unit must exist.
 
+In this value, Quadlet expands the `%N` specifier to the container's service name (the
+`ServiceName=` value if set, otherwise the name derived from the unit file), for example
+`Pod=%N.pod`. The expansion happens while the unit is generated, and `%N` is the only
+specifier resolved in this key.
+
 Quadlet will add all the necessary parameters to link between the container and the pod and between their corresponding services.
 
 
@@ -443,6 +448,7 @@ DefaultDependencies=false
 By default, the container is named `systemd-<unitname>`. Use `ContainerName=` to override.
 
 Avoid using systemd specifiers like `%N` in resource names—they break inter-resource linking.
+The exception is `%N` in `Pod=`, which Quadlet expands while generating the unit.
 
 # TEMPLATE UNITS
 

pkg/systemd/quadlet/quadlet.go

@@ -2214,6 +2214,10 @@ func createBasePodmanCommand(unitFile *parser.UnitFile, groupName string) *Podma
 func handlePod(quadletUnitFile, serviceUnitFile *parser.UnitFile, groupName string, unitsInfoMap map[string]*UnitInfo, podman *PodmanCmdline) error {
 	pod, ok := quadletUnitFile.Lookup(groupName, KeyPod)
 	if ok && len(pod) > 0 {
+		// XXX: only %N is handled.
+		// it is difficult to properly implement specifiers handling without consulting systemd.
+		pod = strings.ReplaceAll(pod, "%N", GetContainerServiceName(quadletUnitFile))
+
 		if !strings.HasSuffix(pod, ".pod") {
 			return fmt.Errorf("pod %s is not Quadlet based", pod)
 		}

test/e2e/quadlet/pod-specifier-svc.pod

@@ -0,0 +1 @@
+[Pod]

test/e2e/quadlet/podspecifier.container

@@ -0,0 +1,7 @@
+## assert-podman-args "--pod" "systemd-podspecifier"
+## assert-last-key-contains "Unit" "BindsTo" "podspecifier-pod.service"
+## assert-last-key-contains "Unit" "After" "podspecifier-pod.service"
+
+[Container]
+Image=localhost/imagename
+Pod=%N.pod

test/e2e/quadlet/podspecifier.pod

@@ -0,0 +1 @@
+[Pod]

test/e2e/quadlet/podspecifier.servicename.container

@@ -0,0 +1,8 @@
+## assert-podman-args "--pod" "systemd-pod-specifier-svc"
+## assert-last-key-contains "Unit" "BindsTo" "pod-specifier-svc-pod.service"
+## assert-last-key-contains "Unit" "After" "pod-specifier-svc-pod.service"
+
+[Container]
+Image=localhost/imagename
+ServiceName=pod-specifier-svc
+Pod=%N.pod

test/e2e/quadlet_test.go

@@ -1238,6 +1238,8 @@ BOGUS=foo
 		Entry("Container - Mount overriding service name", "mount.servicename.container", []string{"service-name.volume"}),
 		Entry("Container - Quadlet Network overriding service name", "network.quadlet.servicename.container", []string{"service-name.network"}),
 		Entry("Container - Quadlet Volume overriding service name", "volume.servicename.container", []string{"service-name.volume"}),
+		Entry("Container - Pod with %N specifier", "podspecifier.container", []string{"podspecifier.pod"}),
+		Entry("Container - Pod with %N specifier and ServiceName", "podspecifier.servicename.container", []string{"pod-specifier-svc.pod"}),
 		Entry("Container - Quadlet build with multiple tags", "build.multiple-tags.container", []string{"multiple-tags.build"}),
 		Entry("Container - Artifact Mount", "artifact-mount.container", []string{"basic.artifact"}),
 		Entry("Container - Reuse another container's network", "network.reuse.container", []string{"basic.container"}),