strmap: set errno to ENOENT even if we return NULL.

It seems redundant: strmap_get() and strmap_del() can only return NULL
when the string is not a member.  However, it became clear in writing
ccan/tsort that it's much more convenient for callers if we set errno
in this case too, so they can pass it up.

ccan/strmap/strmap.c

@@ -39,12 +39,13 @@ void *strmap_get_(const struct strmap *map, const char *member)
 {
 	struct strmap *n;
 
-	/* Empty map? */
-	if (!map->u.n)
-		return NULL;
+	/* Not empty map? */
+	if (map->u.n) {
 		n = closest((struct strmap *)map, member);
 		if (streq(member, n->u.s))
 			return n->v;
+	}
+	errno = ENOENT;
 	return NULL;
 }
 
@@ -129,8 +130,10 @@ char *strmap_del_(struct strmap *map, const char *member, void **valuep)
 	u8 direction = 0; /* prevent bogus gcc warning. */
 
 	/* Empty map? */
-	if (!map->u.n)
+	if (!map->u.n) {
+		errno = ENOENT;
 		return NULL;
+	}
 
 	/* Find closest, but keep track of parent. */
 	n = map;
@@ -148,8 +151,10 @@ char *strmap_del_(struct strmap *map, const char *member, void **valuep)
 	}
 
 	/* Did we find it? */
-	if (!streq(member, n->u.s))
+	if (!streq(member, n->u.s)) {
+		errno = ENOENT;
 		return NULL;
+	}
 
 	ret = n->u.s;
 	if (valuep)

ccan/strmap/strmap.h

@@ -77,7 +77,7 @@ static inline bool strmap_empty_(const struct strmap *map)
  * @map: the typed strmap to search.
  * @member: the string to search for.
  *
- * Returns the value, or NULL if it isn't in the map.
+ * Returns the value, or NULL if it isn't in the map (and sets errno = ENOENT).
  *
  * Example:
  *	int *val = strmap_get(&map, "hello");
@@ -118,7 +118,9 @@ bool strmap_add_(struct strmap *map, const char *member, const void *value);
  * @member: the string to remove from the map.
  * @valuep: the value (if non-NULL)
  *
- * This returns the string which was passed to strmap_map(), or NULL.
+ * This returns the string which was passed to strmap_map(), or NULL if
+ * it was not in the map (and sets errno = ENOENT).
+ *
  * This means that if you allocated a string (eg. using strdup()), you
  * can free it here.  Similarly, the value is returned in @valuep if
  * @valuep is not NULL.

ccan/strmap/test/run.c

@@ -14,20 +14,25 @@ int main(void)
 	char *v;
 
 	/* This is how many tests you plan to run */
-	plan_tests(32);
+	plan_tests(42);
 
 	strmap_init(&map);
 
 	ok1(!strmap_get(&map, str));
+	ok1(errno == ENOENT);
 	ok1(!strmap_get(&map, none));
+	ok1(errno == ENOENT);
 	ok1(!strmap_del(&map, str, NULL));
+	ok1(errno == ENOENT);
 	ok1(!strmap_del(&map, none, NULL));
+	ok1(errno == ENOENT);
 
 	ok1(strmap_add(&map, str, val));
 	ok1(strmap_get(&map, str) == val);
 	/* We compare the string, not the pointer. */
 	ok1(strmap_get(&map, dup) == val);
 	ok1(!strmap_get(&map, none));
+	ok1(errno == ENOENT);
 
 	/* Add a duplicate should fail. */
 	ok1(!strmap_add(&map, dup, val));
@@ -38,18 +43,23 @@ int main(void)
 	ok1(strmap_del(&map, dup, &v) == str);
 	ok1(v == val);
 	ok1(!strmap_get(&map, str));
+	ok1(errno == ENOENT);
 	ok1(!strmap_get(&map, none));
+	ok1(errno == ENOENT);
 
 	/* Try insert and delete of empty string. */
 	ok1(strmap_add(&map, none, none));
 	ok1(strmap_get(&map, none) == none);
 	ok1(!strmap_get(&map, str));
+	ok1(errno == ENOENT);
 
 	/* Delete should return original string. */
 	ok1(strmap_del(&map, "", &v) == none);
 	ok1(v == none);
 	ok1(!strmap_get(&map, str));
+	ok1(errno == ENOENT);
 	ok1(!strmap_get(&map, none));
+	ok1(errno == ENOENT);
 
 	/* Both at once... */
 	ok1(strmap_add(&map, none, none));