Commit cab9da35bd

@@ -1305,7 +1305,7 @@ test "realloc large object to larger alignment" {
 }
 
 test "large object shrinks to small but allocation fails during shrink" {
-    var failing_allocator = std.testing.FailingAllocator.init(std.heap.page_allocator, 3);
+    var failing_allocator = std.testing.FailingAllocator.init(std.heap.page_allocator, .{ .fail_index = 3 });
     var gpa = GeneralPurposeAllocator(.{}){ .backing_allocator = failing_allocator.allocator() };
     defer std.testing.expect(gpa.deinit() == .ok) catch @panic("leak");
     const allocator = gpa.allocator();

@@ -164,8 +164,8 @@ test "memory pool: preheating (success)" {
 }
 
 test "memory pool: preheating (failure)" {
-    var failer = std.testing.FailingAllocator.init(std.testing.allocator, 0);
-    try std.testing.expectError(error.OutOfMemory, MemoryPool(u32).initPreheated(failer.allocator(), 5));
+    var failer = std.testing.failing_allocator;
+    try std.testing.expectError(error.OutOfMemory, MemoryPool(u32).initPreheated(failer, 5));
 }
 
 test "memory pool: growable" {

@@ -397,7 +397,7 @@ test "skipValue" {
 }
 
 fn testEnsureStackCapacity(do_ensure: bool) !void {
-    var fail_alloc = std.testing.FailingAllocator.init(std.testing.allocator, 1);
+    var fail_alloc = std.testing.FailingAllocator.init(std.testing.allocator, .{ .fail_index = 1 });
     const failing_allocator = fail_alloc.allocator();
 
     const nestings = 999; // intentionally not a power of 2.

@@ -461,8 +461,7 @@ test "parse into tagged union errors" {
     try testing.expectError(error.UnexpectedToken, parseFromSliceLeaky(T, arena.allocator(), "{\"nothing\":{\"no\":0}}", .{}));
 
     // Allocator failure
-    var fail_alloc = testing.FailingAllocator.init(testing.allocator, 0);
-    try testing.expectError(error.OutOfMemory, parseFromSlice(T, fail_alloc.allocator(), "{\"string\"\"foo\"}", .{}));
+    try testing.expectError(error.OutOfMemory, parseFromSlice(T, testing.failing_allocator, "{\"string\"\"foo\"}", .{}));
 }
 
 test "parse into struct with no fields" {

@@ -1,19 +1,33 @@
 const std = @import("../std.zig");
 const mem = std.mem;
 
+pub const Config = struct {
+    /// The number of successful allocations you can expect from this allocator.
+    /// The next allocation will fail. For example, with `fail_index` equal to
+    /// 2, the following test will pass:
+    ///
+    /// var a = try failing_alloc.create(i32);
+    /// var b = try failing_alloc.create(i32);
+    /// testing.expectError(error.OutOfMemory, failing_alloc.create(i32));
+    fail_index: usize = std.math.maxInt(usize),
+
+    /// Number of successful resizes to expect from this allocator. The next resize will fail.
+    resize_fail_index: usize = std.math.maxInt(usize),
+};
+
 /// Allocator that fails after N allocations, useful for making sure out of
 /// memory conditions are handled correctly.
 ///
 /// To use this, first initialize it and get an allocator with
 ///
 /// `const failing_allocator = &FailingAllocator.init(<allocator>,
-///                                                   <fail_index>).allocator;`
+///                                                   <config>).allocator;`
 ///
 /// Then use `failing_allocator` anywhere you would have used a
 /// different allocator.
 pub const FailingAllocator = struct {
-    index: usize,
-    fail_index: usize,
+    alloc_index: usize,
+    resize_index: usize,
     internal_allocator: mem.Allocator,
     allocated_bytes: usize,
     freed_bytes: usize,
@@ -21,28 +35,24 @@ pub const FailingAllocator = struct {
     deallocations: usize,
     stack_addresses: [num_stack_frames]usize,
     has_induced_failure: bool,
+    fail_index: usize,
+    resize_fail_index: usize,
 
     const num_stack_frames = if (std.debug.sys_can_stack_trace) 16 else 0;
 
-    /// `fail_index` is the number of successful allocations you can
-    /// expect from this allocator. The next allocation will fail.
-    /// For example, if this is called with `fail_index` equal to 2,
-    /// the following test will pass:
-    ///
-    /// var a = try failing_alloc.create(i32);
-    /// var b = try failing_alloc.create(i32);
-    /// testing.expectError(error.OutOfMemory, failing_alloc.create(i32));
-    pub fn init(internal_allocator: mem.Allocator, fail_index: usize) FailingAllocator {
+    pub fn init(internal_allocator: mem.Allocator, config: Config) FailingAllocator {
         return FailingAllocator{
             .internal_allocator = internal_allocator,
-            .fail_index = fail_index,
-            .index = 0,
+            .alloc_index = 0,
+            .resize_index = 0,
             .allocated_bytes = 0,
             .freed_bytes = 0,
             .allocations = 0,
             .deallocations = 0,
             .stack_addresses = undefined,
             .has_induced_failure = false,
+            .fail_index = config.fail_index,
+            .resize_fail_index = config.resize_fail_index,
         };
     }
 
@@ -64,7 +74,7 @@ pub const FailingAllocator = struct {
         return_address: usize,
     ) ?[*]u8 {
         const self: *FailingAllocator = @ptrCast(@alignCast(ctx));
-        if (self.index == self.fail_index) {
+        if (self.alloc_index == self.fail_index) {
             if (!self.has_induced_failure) {
                 @memset(&self.stack_addresses, 0);
                 var stack_trace = std.builtin.StackTrace{
@@ -80,7 +90,7 @@ pub const FailingAllocator = struct {
             return null;
         self.allocated_bytes += len;
         self.allocations += 1;
-        self.index += 1;
+        self.alloc_index += 1;
         return result;
     }
 
@@ -92,6 +102,8 @@ pub const FailingAllocator = struct {
         ra: usize,
     ) bool {
         const self: *FailingAllocator = @ptrCast(@alignCast(ctx));
+        if (self.resize_index == self.resize_fail_index)
+            return false;
         if (!self.internal_allocator.rawResize(old_mem, log2_old_align, new_len, ra))
             return false;
         if (new_len < old_mem.len) {
@@ -99,6 +111,7 @@ pub const FailingAllocator = struct {
         } else {
             self.allocated_bytes += new_len - old_mem.len;
         }
+        self.resize_index += 1;
         return true;
     }
 

@@ -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();

@@ -14,7 +14,7 @@ pub var allocator_instance = b: {
 };
 
 pub const failing_allocator = failing_allocator_instance.allocator();
-pub var failing_allocator_instance = FailingAllocator.init(base_allocator_instance.allocator(), 0);
+pub var failing_allocator_instance = FailingAllocator.init(base_allocator_instance.allocator(), .{ .fail_index = 0 });
 
 pub var base_allocator_instance = std.heap.FixedBufferAllocator.init("");
 
@@ -1081,16 +1081,16 @@ pub fn checkAllAllocationFailures(backing_allocator: std.mem.Allocator, comptime
 
     // 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, std.math.maxInt(usize));
+        var failing_allocator_inst = std.testing.FailingAllocator.init(backing_allocator, .{});
         args.@"0" = failing_allocator_inst.allocator();
 
         try @call(.auto, test_fn, args);
-        break :x failing_allocator_inst.index;
+        break :x failing_allocator_inst.alloc_index;
     };
 
     var fail_index: usize = 0;
     while (fail_index < needed_alloc_count) : (fail_index += 1) {
-        var failing_allocator_inst = std.testing.FailingAllocator.init(backing_allocator, fail_index);
+        var failing_allocator_inst = std.testing.FailingAllocator.init(backing_allocator, .{ .fail_index = fail_index });
         args.@"0" = failing_allocator_inst.allocator();
 
         if (@call(.auto, test_fn, args)) |_| {