std-aux: add c_list_is_empty_or_single() helper

Having a list with only one element is often interesting to know. For
example, if you are about to unlink an element, you may want to check
whether afterwards the list is empty.

Add c_list_is_empty_or_single() for that. It is probably more efficient than
plain c_list_length_is(list, 1) and also a better name.

2 files changed, 14 insertions, 0 deletions

diff --git a/src/libnm-core-impl/tests/test-general.c b/src/libnm-core-impl/tests/test-general.c
index 8a98265abb..84d9caaeae 100644
--- a/src/libnm-core-impl/tests/test-general.c
+++ b/src/libnm-core-impl/tests/test-general.c
@@ -1417,6 +1417,7 @@ _do_test_c_list_sort(CListSort *elements, guint n_list, gboolean headless)
 
     g_assert(!c_list_is_empty(&head));
     g_assert(c_list_length(&head) == n_list);
+    g_assert(c_list_is_empty_or_single(&head) == (n_list <= 1));
 
     el_prev = NULL;
     c_list_for_each (iter, &head) {
@@ -1443,6 +1444,10 @@ test_c_list_sort(void)
     guint              n_list;
     guint              repeat;
 
+    g_assert(!c_list_is_linked(NULL));
+    g_assert(c_list_is_empty(NULL));
+    g_assert(c_list_is_empty_or_single(NULL));
+
     {
         CList head;
 
@@ -1450,6 +1455,7 @@ test_c_list_sort(void)
         c_list_sort(&head, _c_list_sort_cmp, NULL);
         g_assert(c_list_length(&head) == 0);
         g_assert(c_list_is_empty(&head));
+        g_assert(c_list_is_empty_or_single(&head));
     }
 
     elements = g_new0(CListSort, N_ELEMENTS);
@@ -1517,6 +1523,8 @@ _do_test_c_list_insert_sorted(CListSort *elements, guint n_list, bool append_equ
     g_assert(c_list_length_is(&head, n_list));
     g_assert(!c_list_length_is(&head, n_list + 1));
 
+    g_assert(c_list_is_empty_or_single(&head) == (n_list <= 1));
+
     el_prev = NULL;
     c_list_for_each_entry (el, &head, lst) {
         if (el_prev) {
diff --git a/src/libnm-std-aux/c-list-util.h b/src/libnm-std-aux/c-list-util.h
index 4800a3cc11..ae2f07ec8c 100644
--- a/src/libnm-std-aux/c-list-util.h
+++ b/src/libnm-std-aux/c-list-util.h
@@ -42,6 +42,12 @@ c_list_length_is(const CList *list, unsigned long check_len)
     return n == check_len;
 }
 
+static inline int
+c_list_is_empty_or_single(const CList *list)
+{
+    return !list || (list->next->next == list);
+}
+
 #define c_list_for_each_prev(_iter, _list) \
     for (_iter = (_list)->prev; (_iter) != (_list); _iter = (_iter)->prev)