basic/list: drop LIST_IS_EMPTY

This was a trivial wrapper that didn't provide any added value. With more
complicated structures like strvs, hashmaps, sets, and arrays, it is possible
to have an empty container. But in case of a list, the list is empty only when
the head is missing.

Also, we generally want the positive condition, so we replace many
if (!LIST_IS_EMPTY(x)) with just if (x).

src/core/cgroup.c

@@ -1689,7 +1689,7 @@ static bool unit_get_needs_bpf_foreign_program(Unit *u) {
         if (!c)
                 return false;
 
-        return !LIST_IS_EMPTY(c->bpf_foreign_programs);
+        return !!c->bpf_foreign_programs;
 }
 
 static bool unit_get_needs_socket_bind(Unit *u) {

src/core/dbus-cgroup.c

@@ -737,7 +737,7 @@ static int bus_cgroup_set_transient_property(
 
                         unit_write_setting(u, flags, name, buf);
 
-                        if (!LIST_IS_EMPTY(c->bpf_foreign_programs)) {
+                        if (c->bpf_foreign_programs) {
                                 r = bpf_foreign_supported();
                                 if (r < 0)
                                         return r;

src/core/dbus-execute.c

@@ -1698,16 +1698,16 @@ int bus_exec_context_set_transient_property(
                         return r;
 
                 if (!UNIT_WRITE_FLAGS_NOOP(flags)) {
-                        if (LIST_IS_EMPTY(options)) {
-                                c->root_image_options = mount_options_free_all(c->root_image_options);
-                                unit_write_settingf(u, flags, name, "%s=", name);
-                        } else {
+                        if (options) {
                                 LIST_JOIN(mount_options, c->root_image_options, options);
                                 unit_write_settingf(
                                                 u, flags|UNIT_ESCAPE_SPECIFIERS, name,
                                                 "%s=%s",
                                                 name,
                                                 format_str);
+                        } else {
+                                c->root_image_options = mount_options_free_all(c->root_image_options);
+                                unit_write_settingf(u, flags, name, "%s=", name);
                         }
                 }
 

src/core/dbus-util.c

@@ -216,7 +216,7 @@ int bus_read_mount_options(
         if (r < 0)
                 return r;
 
-        if (!LIST_IS_EMPTY(options)) {
+        if (options) {
                 if (ret_format_str) {
                         char *final = strjoin(*ret_format_str, !isempty(*ret_format_str) ? separator : "", format_str);
                         if (!final)

src/core/load-fragment.c

@@ -1691,11 +1691,11 @@ int config_parse_root_image_options(
                 LIST_APPEND(mount_options, options, TAKE_PTR(o));
         }
 
-        /* empty spaces/separators only */
-        if (LIST_IS_EMPTY(options))
-                c->root_image_options = mount_options_free_all(c->root_image_options);
-        else
+        if (options)
                 LIST_JOIN(mount_options, c->root_image_options, options);
+        else
+                /* empty spaces/separators only */
+                c->root_image_options = mount_options_free_all(c->root_image_options);
 
         return 0;
 }

src/core/unit.c

@@ -4138,7 +4138,7 @@ int unit_patch_contexts(Unit *u) {
                     cc->device_policy == CGROUP_DEVICE_POLICY_AUTO)
                         cc->device_policy = CGROUP_DEVICE_POLICY_CLOSED;
 
-                if ((ec->root_image || !LIST_IS_EMPTY(ec->mount_images)) &&
+                if ((ec->root_image || ec->mount_images) &&
                     (cc->device_policy != CGROUP_DEVICE_POLICY_AUTO || cc->device_allow)) {
 
                         /* When RootImage= or MountImages= is specified, the following devices are touched. */