systemctl: warn if trying to disable a unit with no install info

Trying to disable a unit with no install info is mostly useless, so
adding a warning like we do for enable (with the new dbus method
'DisableUnitFilesWithFlagsAndInstallInfo()'). Note that it would
still find and remove symlinks to the unit in /etc, regardless of
whether it has install info or not, just like before. And if there are
actually files to remove, we suppress the warning.

Fixes #17689

1 files changed, 17 insertions, 4 deletions

diff --git a/src/shared/install.c b/src/shared/install.c
index 51aa60bb52..c38ba1bd7a 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -2790,25 +2790,38 @@ static int do_unit_file_disable(
 
         _cleanup_(install_context_done) InstallContext ctx = { .scope = scope };
         _cleanup_set_free_free_ Set *remove_symlinks_to = NULL;
+        InstallInfo *info;
+        bool has_install_info = false;
         int r;
 
         STRV_FOREACH(name, names) {
                 if (!unit_name_is_valid(*name, UNIT_NAME_ANY))
                         return install_changes_add(changes, n_changes, -EUCLEAN, *name, NULL);
 
-                r = install_info_add(&ctx, *name, NULL, lp->root_dir, /* auxiliary= */ false, NULL);
+                r = install_info_add(&ctx, *name, NULL, lp->root_dir, /* auxiliary= */ false, &info);
+                if (r >= 0)
+                        r = install_info_traverse(&ctx, lp, info, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS, NULL);
+
                 if (r < 0)
-                        return r;
+                        return install_changes_add(changes, n_changes, r, *name, NULL);
+
+                /* If we enable multiple units, some with install info and others without,
+                 * the "empty [Install] section" warning is not shown. Let's make the behavior
+                 * of disable align with that. */
+                has_install_info = has_install_info || install_info_has_rules(info) || install_info_has_also(info);
         }
 
         r = install_context_mark_for_removal(&ctx, lp, &remove_symlinks_to, config_path, changes, n_changes);
+        if (r >= 0)
+                r = remove_marked_symlinks(remove_symlinks_to, config_path, lp, flags & UNIT_FILE_DRY_RUN, changes, n_changes);
+
         if (r < 0)
                 return r;
 
-        return remove_marked_symlinks(remove_symlinks_to, config_path, lp, flags & UNIT_FILE_DRY_RUN, changes, n_changes);
+        /* The warning is shown only if it's a no-op */
+        return install_changes_have_modification(*changes, *n_changes) || has_install_info;
 }
 
-
 int unit_file_disable(
                 LookupScope scope,
                 UnitFileFlags flags,