sysext: use [] in json mode when giving the extension status

The json mode was returning the string `none` when unmerged and
an array for merged extensions. Return an empty array instead.

Instead of branching on the output format, always add an empty strv
for an unmerged hierarchy: the table code renders an empty strv as
the ersatz string ("-") in text mode and as an empty array in json
mode. This also changes the human-readable output from "none" to "-".

It also updated the TEST-50-DISSECT.sysext.sh test. Technically
this is a compatbility break but its also arguably a bugfix.

NEWS

@@ -1,5 +1,15 @@
 systemd System and Service Manager
 
+CHANGES WITH 263:
+
+        Feature Removals and Incompatible Changes:
+
+        * The "extensions" field of "systemd-sysext status --json=" and
+          "systemd-confext status --json=" is now always an array. A hierarchy
+          that is not merged reports an empty array, instead of the string
+          "none" returned previously. In the human-readable table output a
+          hierarchy that is not merged is now shown as "-" instead of "none".
+
 CHANGES WITH 262 in spe:
 
         Announcements of Future Feature Removals and Incompatible Changes:

src/sysext/sysext.c

@@ -10,7 +10,6 @@
 #include "sd-json.h"
 #include "sd-varlink.h"
 
-#include "ansi-color.h"
 #include "argv-util.h"
 #include "blkid-util.h"
 #include "blockdev-util.h"
@@ -2592,8 +2591,7 @@ static int verb_status(int argc, char *argv[], uintptr_t _data, void *userdata)
                         r = table_add_many(
                                         t,
                                         TABLE_PATH, *p,
-                                        TABLE_STRING, "none",
-                                        TABLE_SET_COLOR, ansi_grey(),
+                                        TABLE_STRV, STRV_EMPTY,
                                         TABLE_EMPTY);
                         if (r < 0)
                                 return table_log_add_error(r);

test/units/TEST-50-DISSECT.dissect.sh

@@ -1080,7 +1080,9 @@ systemd-confext merge
 grep -q -F "MARKER_CONFEXT_123" /etc/testfile
 (! /etc/testscript)
 systemd-confext status
+systemd-confext status --json=pretty | jq -e 'any(.[]; .hierarchy == "/etc" and .extensions == ["test"] and .since != null)' >/dev/null
 systemd-confext unmerge
+systemd-confext status --json=pretty | jq -e 'any(.[]; .hierarchy == "/etc" and .extensions == [] and .since == null)' >/dev/null
 rm -rf /run/confexts/
 
 cleanup_sysupdate_notify_confext_mutable() {

test/units/TEST-50-DISSECT.sysext.sh

@@ -363,6 +363,25 @@ extension_verify_mount_option() (
     done
 )
 
+extension_verify_status_json() (
+    local root=${1:-}
+    local hierarchy=${2:?}
+    local expected_extensions=${3:?}
+    local status_json since_filter
+
+    # Whether a hierarchy is merged is told by "since", not by "extensions": an empty array is also
+    # reported for a hierarchy merged in mutable mode without any extensions.
+    if [[ "$expected_extensions" == "[]" ]]; then
+        since_filter='.since == null'
+    else
+        since_filter='.since != null'
+    fi
+
+    status_json=$(run_systemd_sysext "$root" status --json=pretty)
+    jq -e --arg h "$hierarchy" --argjson e "$expected_extensions" \
+       "any(.[]; .hierarchy == \$h and .extensions == \$e and $since_filter)" >/dev/null <<<"$status_json"
+)
+
 run_systemd_sysext() {
     local root=${1:-}
     shift
@@ -400,9 +419,11 @@ prepare_read_only_hierarchy "$fake_root" "$hierarchy"
 run_systemd_sysext "$fake_root" merge
 (! touch "$fake_root$hierarchy/should-still-fail-on-read-only-fs")
 extension_verify_after_merge "$fake_root" "$hierarchy" -e -h
+extension_verify_status_json "$fake_root" "$hierarchy" '["test-extension"]'
 
 run_systemd_sysext "$fake_root" unmerge
 extension_verify_after_unmerge "$fake_root" "$hierarchy" -h
+extension_verify_status_json "$fake_root" "$hierarchy" '[]'
 (! touch "$fake_root$hierarchy/should-still-fail-on-read-only-fs")
 )
 
@@ -1270,7 +1291,7 @@ prepare_read_only_hierarchy "$fake_root" "$hierarchy"
 
 # Should be a no-op, thus we also don't run unmerge afterwards (otherwise the test is broken)
 run_systemd_sysext "$fake_root" merge
-if run_systemd_sysext "$fake_root" status --json=pretty |  jq -r '.[].extensions' | grep -v '^none$' ; then
+if ! extension_verify_status_json "$fake_root" "$hierarchy" '[]'; then
     echo >&2 "Extension got loaded for an initrd structure passed as --root= while the extension does not declare itself compatible with the initrd scope"
     exit 1
 fi