std: enable FailingAllocator to fail on resize

Now that allocator.resize() is allowed to fail, programs may wish to
test code paths that handle resize() failure. The simplest way to do
this now is to replace the vtable of the testing allocator with one
that uses Allocator.noResize for the 'resize' function pointer.

An alternative way to support this testing capability is to augment the
FailingAllocator (which is already useful for testing allocation failure
scenarios) to intentionally fail on calls to resize(). To do this, add a
'resize_fail_index' parameter to the FailingAllocator that causes
resize() to fail after the given number of calls.

1 files changed, 6 insertions, 16 deletions

diff --git a/lib/std/array_list.zig b/lib/std/array_list.zig
index ec38fad50b..a258475517 100644
--- a/lib/std/array_list.zig
+++ b/lib/std/array_list.zig
@@ -1587,13 +1587,8 @@ test "std.ArrayListUnmanaged(u8) implements writer" {
 }
 
 test "shrink still sets length when resizing is disabled" {
-    // Use the testing allocator but with resize disabled.
-    var a = testing.allocator;
-    a.vtable = &.{
-        .alloc = a.vtable.alloc,
-        .resize = Allocator.noResize,
-        .free = a.vtable.free,
-    };
+    var failing_allocator = testing.FailingAllocator.init(testing.allocator, .{ .resize_fail_index = 0 });
+    const a = failing_allocator.allocator();
 
     {
         var list = ArrayList(i32).init(a);
@@ -1620,13 +1615,9 @@ test "shrink still sets length when resizing is disabled" {
 }
 
 test "shrinkAndFree with a copy" {
-    // Use the testing allocator but with resize disabled.
-    var a = testing.allocator;
-    a.vtable = &.{
-        .alloc = a.vtable.alloc,
-        .resize = Allocator.noResize,
-        .free = a.vtable.free,
-    };
+    var failing_allocator = testing.FailingAllocator.init(testing.allocator, .{ .resize_fail_index = 0 });
+    const a = failing_allocator.allocator();
+
     var list = ArrayList(i32).init(a);
     defer list.deinit();
 
@@ -1748,8 +1739,7 @@ test "ArrayListAligned/ArrayListAlignedUnmanaged accepts unaligned slices" {
 
 test "std.ArrayList(u0)" {
     // An ArrayList on zero-sized types should not need to allocate
-    var failing_allocator = testing.FailingAllocator.init(testing.allocator, 0);
-    const a = failing_allocator.allocator();
+    const a = testing.failing_allocator;
 
     var list = ArrayList(u0).init(a);
     defer list.deinit();