eina: add eina_list_data_idx().

Summary:
Now the developer has to iterate the whole list to find the
index of the first occurence of the data.
I see that it is possible to get the index of the item for
the genlist widget, but for the eina_list not.

With these APIs it will be easier to implement *index_get
functions for the rest of widgets which contain items (Elm_List,
Elm_Ctxpopup etc.).

These functions returns the index of the given data or node in the eina_list.

Reviewers: Hermet, cedric

Subscribers: raster, cedric

Differential Revision: https://phab.enlightenment.org/D2189

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>

src/lib/eina/eina_list.c

@@ -1569,3 +1569,23 @@ eina_list_accessor_new(const Eina_List *list)
 
    return &ac->accessor;
 }
+
+EAPI int
+eina_list_data_idx(const Eina_List *list, void *data)
+{
+   const Eina_List *l;
+   void *list_data;
+   int ret = 0;
+
+   if (!list) return -1;
+   EINA_MAGIC_CHECK_LIST(list, -1);
+
+   EINA_LIST_FOREACH(list, l, list_data)
+     {
+        if (list_data == data)
+          return ret;
+        ret++;
+     }
+
+   return -1;
+}

src/lib/eina/eina_list.h

@@ -1344,6 +1344,22 @@ EAPI Eina_Iterator        *eina_list_iterator_reversed_new(const Eina_List *list
  */
 EAPI Eina_Accessor        *eina_list_accessor_new(const Eina_List *list) EINA_MALLOC EINA_WARN_UNUSED_RESULT;
 
+/**
+ * @brief Find the member of the list and return the index.
+ * 
+ * @param list The list.
+ * @param data The data member.
+ * @return The index of data member if found, @c -1 otherwise.
+ *
+ * This function searches in @p list from beginning to end for the
+ * first member whose data pointer is @p data. If it is found, the
+ * index of the data will be returned, otherwise @c -1 will be returned.
+ *
+ * @warning @p list must be a pointer to the first element of the list.
+ * 
+ */
+EAPI int                   eina_list_data_idx(const Eina_List *list, void *data);
+
 /**
  * @def EINA_LIST_FOREACH
  * @brief Macro to iterate over a list.