string_list: add a function string_list_remove_empty_items()

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Acked-by: Johan Herland <johan@herland.net>
Signed-off-by: Jeff King <peff@peff.net>

Documentation/technical/api-string-list.txt

@@ -38,7 +38,8 @@ member (you need this if you add things later) and you should set the
   `unsorted_string_list_delete_item`.
 
 . Can remove items not matching a criterion from a sorted or unsorted
-  list using `filter_string_list`.
+  list using `filter_string_list`, or remove empty strings using
+  `string_list_remove_empty_items`.
 
 . Finally it should free the list using `string_list_clear`.
 
@@ -75,6 +76,12 @@ Functions
 	to be deleted.  Preserve the order of the items that are
 	retained.
 
+`string_list_remove_empty_items`::
+
+	Remove any empty strings from the list.  If free_util is true,
+	call free() on the util members of any items that have to be
+	deleted.  Preserve the order of the items that are retained.
+
 `string_list_longest_prefix`::
 
 	Return the longest string within a string_list that is a

string-list.c

@@ -136,6 +136,15 @@ void filter_string_list(struct string_list *list, int free_util,
 	list->nr = dst;
 }
 
+static int item_is_not_empty(struct string_list_item *item, void *unused)
+{
+	return *item->string != '\0';
+}
+
+void string_list_remove_empty_items(struct string_list *list, int free_util) {
+	filter_string_list(list, free_util, item_is_not_empty, NULL);
+}
+
 char *string_list_longest_prefix(const struct string_list *prefixes,
 				 const char *string)
 {

string-list.h

@@ -38,6 +38,13 @@ int for_each_string_list(struct string_list *list,
 void filter_string_list(struct string_list *list, int free_util,
 			string_list_each_func_t want, void *cb_data);
 
+/*
+ * Remove any empty strings from the list.  If free_util is true, call
+ * free() on the util members of any items that have to be deleted.
+ * Preserve the order of the items that are retained.
+ */
+void string_list_remove_empty_items(struct string_list *list, int free_util);
+
 /*
  * Return the longest string in prefixes that is a prefix (in the
  * sense of prefixcmp()) of string, or NULL if no such prefix exists.