From f2084ab74a8279db4a4607d97d49d27b0acda4db Mon Sep 17 00:00:00 2001
From: Alexander Mitterholzer <alexandermitterholzer@noreply.codeberg.org>
Date: Fri, 9 Oct 2026 21:55:17 +0200
Subject: [PATCH] std.testing: refuse resizes in checkAllAllocationFailures
 (#37142)

Fixes #37141

With resizes refused every growth goes through alloc, which is what the check counts, so the count no longer depends on the backing allocator.

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/37142
Reviewed-by: Andrew Kelley <andrew@ziglang.org>
---
 lib/std/testing.zig | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/lib/std/testing.zig b/lib/std/testing.zig
index 53c52b71073a80a1360ca4d9bd39b9e2d603eb1d..fe785191d9bd4f537983bb1c764f69eb1510467f 100644
--- a/lib/std/testing.zig
+++ b/lib/std/testing.zig
@@ -1149,7 +1149,9 @@ pub fn checkAllAllocationFailures(
 ) !void {
     // Try it once with unlimited memory, make sure it works
     const needed_alloc_count = x: {
-        var failing_allocator_inst = std.testing.FailingAllocator.init(backing_allocator, .{});
+        var failing_allocator_inst = std.testing.FailingAllocator.init(backing_allocator, .{
+            .resize_fail_index = 0,
+        });
 
         try @call(.auto, test_fn, .{failing_allocator_inst.allocator()} ++ extra_args);
         break :x failing_allocator_inst.alloc_index;
@@ -1158,6 +1160,7 @@ pub fn checkAllAllocationFailures(
     for (0..needed_alloc_count) |fail_index| {
         var failing_allocator_inst = std.testing.FailingAllocator.init(backing_allocator, .{
             .fail_index = fail_index,
+            .resize_fail_index = 0,
         });
 
         if (@call(.auto, test_fn, .{failing_allocator_inst.allocator()} ++ extra_args)) |_| {
@@ -1239,6 +1242,24 @@ test "checkAllAllocationFailures provide result type to 'extra_args' argument" {
     );
 }
 
+test "checkAllAllocationFailures does not depend on in-place resizes" {
+    // `std.testing.allocator` never reuses memory, so whether a list can grow in place depends
+    // on where in its bucket it landed, which differs from one run to the next.
+    const S = struct {
+        fn f(gpa: std.mem.Allocator) !void {
+            var a: std.ArrayList(u8) = .empty;
+            defer a.deinit(gpa);
+            var b: std.ArrayList(u8) = .empty;
+            defer b.deinit(gpa);
+            for (0..2000) |i| {
+                try a.append(gpa, @truncate(i));
+                try b.append(gpa, @truncate(i));
+            }
+        }
+    };
+    try checkAllAllocationFailures(std.testing.allocator, S.f, .{});
+}
+
 /// Given a type, references all the declarations inside, so that the semantic analyzer sees them.
 pub fn refAllDecls(comptime T: type) void {
     if (!builtin.is_test) return;
-- 
2.54.0