string_list: add function string_list_append_nodup()

Add a new function that appends a string to a string_list without
copying it.  This can be used to pass ownership of an already-copied
string to a string_list that has strdup_strings set.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-string-list.txt

@@ -20,8 +20,8 @@ If you need something advanced, you can manually malloc() the `items`
 member (you need this if you add things later) and you should set the
 `nr` and `alloc` members in that case, too.
 
-. Adds new items to the list, using `string_list_append` or
-  `string_list_insert`.
+. Adds new items to the list, using `string_list_append`,
+  `string_list_append_nodup`, or `string_list_insert`.
 
 . Can check if a string is in the list using `string_list_has_string` or
   `unsorted_string_list_has_string` and get it from the list using
@@ -100,7 +100,18 @@ write `string_list_insert(...)->util = ...;`.
 
 `string_list_append`::
 
-	Append a new string to the end of the string_list.
+	Append a new string to the end of the string_list.  If
+	`strdup_string` is set, then the string argument is copied;
+	otherwise the new `string_list_entry` refers to the input
+	string.
+
+`string_list_append_nodup`::
+
+	Append a new string to the end of the string_list.  The new
+	`string_list_entry` always refers to the input string, even if
+	`strdup_string` is set.  This function can be used to hand
+	ownership of a malloc()ed string to a `string_list` that has
+	`strdup_string` set.
 
 `sort_string_list`::
 

string-list.c

@@ -148,13 +148,23 @@ void print_string_list(const struct string_list *p, const char *text)
 		printf("%s:%p\n", p->items[i].string, p->items[i].util);
 }
 
-struct string_list_item *string_list_append(struct string_list *list, const char *string)
+struct string_list_item *string_list_append_nodup(struct string_list *list,
+						  char *string)
 {
+	struct string_list_item *retval;
 	ALLOC_GROW(list->items, list->nr + 1, list->alloc);
-	list->items[list->nr].string =
-		list->strdup_strings ? xstrdup(string) : (char *)string;
-	list->items[list->nr].util = NULL;
-	return list->items + list->nr++;
+	retval = &list->items[list->nr++];
+	retval->string = string;
+	retval->util = NULL;
+	return retval;
+}
+
+struct string_list_item *string_list_append(struct string_list *list,
+					    const char *string)
+{
+	return string_list_append_nodup(
+			list,
+			list->strdup_strings ? xstrdup(string) : (char *)string);
 }
 
 static int cmp_items(const void *a, const void *b)

string-list.h

@@ -29,6 +29,7 @@ int for_each_string_list(struct string_list *list,
 #define for_each_string_list_item(item,list) \
 	for (item = (list)->items; item < (list)->items + (list)->nr; ++item)
 
+
 /* Use these functions only on sorted lists: */
 int string_list_has_string(const struct string_list *list, const char *string);
 int string_list_find_insert_index(const struct string_list *list, const char *string,
@@ -38,11 +39,28 @@ struct string_list_item *string_list_insert_at_index(struct string_list *list,
 						     int insert_at, const char *string);
 struct string_list_item *string_list_lookup(struct string_list *list, const char *string);
 
+
 /* Use these functions only on unsorted lists: */
+
+/*
+ * Add string to the end of list.  If list->strdup_string is set, then
+ * string is copied; otherwise the new string_list_entry refers to the
+ * input string.
+ */
 struct string_list_item *string_list_append(struct string_list *list, const char *string);
+
+/*
+ * Like string_list_append(), except string is never copied.  When
+ * list->strdup_strings is set, this function can be used to hand
+ * ownership of a malloc()ed string to list without making an extra
+ * copy.
+ */
+struct string_list_item *string_list_append_nodup(struct string_list *list, char *string);
+
 void sort_string_list(struct string_list *list);
 int unsorted_string_list_has_string(struct string_list *list, const char *string);
 struct string_list_item *unsorted_string_list_lookup(struct string_list *list,
 						     const char *string);
+
 void unsorted_string_list_delete_item(struct string_list *list, int i, int free_util);
 #endif /* STRING_LIST_H */