From: Timo Sirainen <timo.sirainen@open-xchange.com>
Date: Thu, 3 Jun 2021 16:04:26 +0000 (+0300)
Subject: lib: Add array_foreach_reverse[_modifiable]()
X-Git-Tag: 2.3.16~56
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=bb618563b778fcb5d22307aaeca4111ca0e0e04a;p=thirdparty%2Fdovecot%2Fcore.git

lib: Add array_foreach_reverse[_modifiable]()

This is especially useful when deleting multiple elements inside the loop.
---

diff --git a/src/lib/array.h b/src/lib/array.h
index 38f8bec0cd..9349e8af47 100644
--- a/src/lib/array.h
+++ b/src/lib/array.h
@@ -72,7 +72,13 @@
 
    array_foreach(&foo_arr, foo) {
      ..
-   } */
+   }
+
+   Note that deleting an element while iterating will cause the iteration to
+   skip over the next element. So deleting a single element and breaking out
+   of the loop is fine, but continuing the loop is likely a bug. Use
+   array_foreach_reverse() instead when deleting multiple elements.
+*/
 #define array_foreach(array, elem) \
 	for (const void *elem ## __foreach_end = \
 		(const char *)(elem = *(array)->v) + (array)->arr.buffer->used; \
@@ -83,6 +89,17 @@
 			buffer_get_modifiable_data((array)->arr.buffer, NULL)) + \
 			(array)->arr.buffer->used; \
 	     elem != elem ## _end; (elem)++)
+
+/* Iterate the array in reverse order. */
+#define array_foreach_reverse(array, elem) \
+	for (elem = CONST_PTR_OFFSET(*(array)->v, (array)->arr.buffer->used); \
+	     (const char *)(elem--) > (const char *)*(array)->v; )
+#define array_foreach_reverse_modifiable(array, elem) \
+	for (elem = ARRAY_TYPE_CAST_MODIFIABLE(array) \
+		((char *)buffer_get_modifiable_data((array)->arr.buffer, NULL) + \
+		 (array)->arr.buffer->used); \
+	     (const char *)(elem--) > (const char *)*(array)->v; )
+
 /* Usage:
    ARRAY(struct foo *) foo_ptrs_arr;
    struct foo *foo;
diff --git a/src/lib/test-array.c b/src/lib/test-array.c
index 7d2d9bb664..e6aade12c4 100644
--- a/src/lib/test-array.c
+++ b/src/lib/test-array.c
@@ -89,6 +89,56 @@ static void test_array_foreach(void)
 	test_assert(foo == array_idx(&foos, i)+1);
 	test_end();
 }
+
+static void test_array_foreach_reverse(void)
+{
+	ARRAY(unsigned int) arr;
+	const unsigned int *i_p;
+	unsigned int i, i2, *imod_p;
+
+	test_begin("array foreach reverse");
+	t_array_init(&arr, 32);
+
+	/* first test that array_foreach() + array_delete() doesn't really
+	   work as we might hope.. */
+	for (i = 1; i <= 5; i++)
+		array_push_back(&arr, &i);
+	array_foreach(&arr, i_p) {
+		i = array_foreach_idx(&arr, i_p);
+		array_delete(&arr, i, 1);
+	}
+	test_assert(array_count(&arr) == 2);
+
+	/* but using array_foreach_reverse() + array_delete() does work: */
+	array_clear(&arr);
+	i2 = 5;
+	for (i = 1; i <= i2; i++)
+		array_push_back(&arr, &i);
+	array_foreach_reverse(&arr, i_p) {
+		i = array_foreach_idx(&arr, i_p);
+		test_assert(*i_p == i2);
+		test_assert(*i_p == i + 1);
+		array_delete(&arr, i, 1);
+		i2--;
+	}
+	test_assert(array_count(&arr) == 0);
+
+	/* also array_foreach_reverse_modifiable() + array_delete() works: */
+	i2 = 5;
+	for (i = 1; i <= i2; i++)
+		array_push_back(&arr, &i);
+	array_foreach_reverse_modifiable(&arr, imod_p) {
+		i = array_foreach_idx(&arr, imod_p);
+		test_assert(*imod_p == i2);
+		test_assert(*imod_p == i + 1);
+		array_delete(&arr, i, 1);
+		i2--;
+	}
+	test_assert(array_count(&arr) == 0);
+
+	test_end();
+}
+
 static void test_array_foreach_elem_string(void)
 {
 	ARRAY(char *) blurbs;
@@ -307,6 +357,7 @@ void test_array(void)
 	test_array_elem();
 	test_array_count();
 	test_array_foreach();
+	test_array_foreach_reverse();
 	test_array_foreach_elem_string();
 	test_array_reverse();
 	test_array_cmp();