Fix plist_sort() by swapping the nodes in the tree instead of their data

The problem was that we swapped potential child node data between nodes,
but their parents would not be updated that way, leading to double frees
or segmentation faults when freeing a plist. This commit instead fixes this
by swapping the actual nodes in the tree.

src/plist.c

@@ -43,6 +43,7 @@
 #endif
 
 #include <node.h>
+#include <node_list.h>
 #include <hashtable.h>
 #include <ptrarray.h>
 
@@ -1515,44 +1516,47 @@ PLIST_API void plist_sort(plist_t plist)
             plist_sort((plist_t)ch);
         }
         #define KEY_DATA(x) (x->data)
-        #define VAL_DATA(x) (x->next->data)
-        #define VAL_COUNT(x) (x->next->count)
-        #define VAL_CHDN(x) (x->next->children)
         #define NEXT_KEY(x) (x->next->next)
-        #define NEXT_VAL(x) (NEXT_KEY(x)->next)
-        #define NEXT_KEY_DATA(x) (NEXT_KEY(x)->data)
-        #define NEXT_VAL_DATA(x) (NEXT_VAL(x)->data)
-        #define NEXT_VAL_CHDN(x) (NEXT_VAL(x)->children)
-        #define NEXT_VAL_COUNT(x) (NEXT_VAL(x)->count)
         #define KEY_STRVAL(x) ((plist_data_t)(KEY_DATA(x)))->strval
-        #define NEXT_KEY_STRVAL(x) ((plist_data_t)(NEXT_KEY_DATA(x)))->strval
         int swapped = 0;
         do {
             swapped = 0;
             node_t *lptr = NULL;
-            node_t *ptr_key = node_first_child((node_t*)plist);
-            while (NEXT_KEY(ptr_key) != lptr) {
-                if (strcmp(KEY_STRVAL(ptr_key), NEXT_KEY_STRVAL(ptr_key)) > 0) {
-                    // backup old values
-                    void* key_data_tmp = KEY_DATA(ptr_key);
-                    void* val_data_tmp = VAL_DATA(ptr_key);
-                    struct node_list_t *val_chdn_tmp = VAL_CHDN(ptr_key);
-                    unsigned int val_count_tmp = VAL_COUNT(ptr_key);
-                    // replace current with next
-                    KEY_DATA(ptr_key) = NEXT_KEY_DATA(ptr_key);
-                    VAL_DATA(ptr_key) = NEXT_VAL_DATA(ptr_key);
-                    VAL_CHDN(ptr_key) = NEXT_VAL_CHDN(ptr_key);
-                    VAL_COUNT(ptr_key) = NEXT_VAL_COUNT(ptr_key);
-                    // replace next with old
-                    NEXT_KEY_DATA(ptr_key) = key_data_tmp;
-                    NEXT_VAL_DATA(ptr_key) = val_data_tmp;
-                    NEXT_VAL_CHDN(ptr_key) = val_chdn_tmp;
-                    NEXT_VAL_COUNT(ptr_key) = val_count_tmp;
+            node_t *cur_key = node_first_child((node_t*)plist);
+
+            while (NEXT_KEY(cur_key) != lptr) {
+                node_t *next_key = NEXT_KEY(cur_key);
+                if (strcmp(KEY_STRVAL(cur_key), KEY_STRVAL(next_key)) > 0) {
+                    node_t *cur_val = cur_key->next;
+                    node_t *next_val = next_key->next;
+                    // we need to swap 2 consecutive nodes with the 2 after them
+                    // a -> b -> [c] -> [d] -> [e] -> [f] -> g -> h
+                    //              cur           next
+                    // swapped:
+                    // a -> b -> [e] -> [f] -> [c] -> [d] -> g -> h
+                    //              next           cur
+                    node_t *tmp_prev = cur_key->prev;
+                    node_t *tmp_next = next_val->next;
+                    cur_key->prev = next_val;
+                    cur_val->next = tmp_next;
+                    next_val->next = cur_key;
+                    next_key->prev = tmp_prev;
+                    if (tmp_prev) {
+                        tmp_prev->next = next_key;
+                    } else {
+                        ((node_t*)plist)->children->begin = next_key;
+                    }
+                    if (tmp_next) {
+                        tmp_next->prev = cur_val;
+                    } else {
+                        ((node_t*)plist)->children->end = cur_val;
+                    }
+                    cur_key = next_key;
                     swapped = 1;
                 }
-                ptr_key = NEXT_KEY(ptr_key);
+                cur_key = NEXT_KEY(cur_key);
             }
-            lptr = ptr_key;
+            lptr = cur_key;
         } while (swapped);
     }
 }