sysupdate: Add ListFeatures() and ListTargets() varlink methods (#42900)

Following on from adding the basic varlink scaffolding to sysupdate,
let’s varlinkify a couple of the D-Bus methods. Because varlink doesn’t
have a concept of object paths, the D-Bus path structure which allows a
target to be selected has been squashed down to a target argument for
each relevant method.

Varlinkify the way to list targets, and also the way to list features
because that was simple to do at the same time.

More methods need varlinkifying in the future, but let’s do it in small
and manageable chunks.

test/units/TEST-72-SYSUPDATE.sh

@@ -249,7 +249,7 @@ verify_version_current() {
 verify_object_fields() {
     local updatectl_output="${1:?}"
 
-    [[ "${updatectl_output}" != *"Unrecognized object field"* ]] || exit 1
+    [[ "${updatectl_output}" != *"Unrecognized object field"* ]]
 }
 
 for sector_size in "${SECTOR_SIZES[@]}"; do
@@ -461,8 +461,16 @@ EOF
     verify_version_current "$blockdev" "$sector_size" v5 2
 
     # Now let's try enabling an optional feature
-    "$SYSUPDATE" features | grep "optional"
-    "$SYSUPDATE" features optional | grep "99-optional"
+    if [[ "$client" == "sysupdate-cli" ]]; then
+        "$SYSUPDATE" features | grep "optional"
+        "$SYSUPDATE" features optional | grep "99-optional"
+    elif [[ "$client" == "varlink" ]]; then
+        [[ $(varlinkctl call "$VARLINK_SOCKET" io.systemd.SysUpdate.ListFeatures '{"target":{"class":"host"}}' | jq -r '.features[] | select(.id=="optional") | .description') == "Optional Feature" ]]
+        varlinkctl call "$VARLINK_SOCKET" io.systemd.SysUpdate.ListFeatures '{"target":{"class":"host"}}' | jq -r '.features[] | select(.id=="optional") | .transfers' | grep "99-optional"
+    else
+        exit 1
+    fi
+
     test ! -f "$WORKDIR/xbootldr/EFI/Linux/uki_v5.efi.extra.d/optional.efi"
     mkdir "$CONFIGDIR/optional.feature.d"
     echo -e "[Feature]\nEnabled=true" > "$CONFIGDIR/optional.feature.d/enable.conf"
@@ -639,8 +647,11 @@ MatchPattern=some-component_@v
 CurrentSymlink=some-component
 EOF
 "$SYSUPDATE" --json=short components | grep -F '{"default":false,"components":["some-component"]}' >/dev/null
+varlinkctl call "$VARLINK_SOCKET" io.systemd.SysUpdate.ListTargets | jq -e '.targets | all(.id.class != "host")' >/dev/null
 mkdir /run/sysupdate.d
 "$SYSUPDATE" --json=short components | grep -F '{"default":false,"components":["some-component"]}' >/dev/null
+varlinkctl call "$VARLINK_SOCKET" io.systemd.SysUpdate.ListTargets | jq -e '.targets | all(.id.class != "host")' >/dev/null
+[[ $(varlinkctl call "$VARLINK_SOCKET" io.systemd.SysUpdate.ListTargets | jq -r '.targets[0].id.name') == "some-component" ]]
 
 # Regression test for https://github.com/systemd/systemd/issues/42330 — the
 # 'pending'/'reboot' verbs and the '--reboot' switch compare the newest installed
@@ -674,8 +685,15 @@ Path=$WORKDIR/blobs
 MatchPattern=tiny-@v.bin
 InstancesMax=1
 EOF
+
 "$SYSUPDATE" --verify=no update
 cmp "$WORKDIR/source/tiny-v1.bin" "$WORKDIR/blobs/tiny-v1.bin"
+
+# Test that listing features when none are configured gives an empty list.
+"$SYSUPDATE" features |& grep "No features." >/dev/null
+[[ $(varlinkctl call "$VARLINK_SOCKET" io.systemd.SysUpdate.ListFeatures '{"target":{"class":"host"}}' | jq -r '.features') == "[]" ]]
+
+# Cleanup
 rm "$CONFIGDIR/01-tiny-url.transfer"
 rm "$WORKDIR/source/tiny-v1.bin"
 rm "$WORKDIR/source/SHA256SUMS"
@@ -1426,4 +1444,8 @@ cmp "$WORKDIR/source/pack-v2" "$WORKDIR/blobs/pack-v2"
 rm -rf "$CONFIGDIR/01-manifest-yes-and-retry.transfer" \
        "$WORKDIR/source/pack-v1" "$WORKDIR/source/pack-v2"
 
+# Test that listing components/targets when none are configured gives an empty list.
+"$SYSUPDATE" components |& grep "No components defined." >/dev/null
+[[ $(varlinkctl call "$VARLINK_SOCKET" io.systemd.SysUpdate.ListTargets | jq -r '.targets') == "[]" ]]
+
 touch /testok