ValidationAllocator

pub fn ValidationAllocator(comptime T: type) type {
    return struct {
        const Self = @This();

        underlying_allocator: T,

        pub fn init(underlying_allocator: T) @This() {
            return .{
                .underlying_allocator = underlying_allocator,
            };
        }

        pub fn allocator(self: *Self) Allocator {
            return .{
                .ptr = self,
                .vtable = &.{
                    .alloc = alloc,
                    .resize = resize,
                    .remap = remap,
                    .free = free,
                },
            };
        }

        fn getUnderlyingAllocatorPtr(self: *Self) Allocator {
            if (T == Allocator) return self.underlying_allocator;
            return self.underlying_allocator.allocator();
        }

        pub fn alloc(
            ctx: *anyopaque,
            n: usize,
            alignment: mem.Alignment,
            ret_addr: usize,
        ) ?[*]u8 {
            assert(n > 0);
            const self: *Self = @ptrCast(@alignCast(ctx));
            const underlying = self.getUnderlyingAllocatorPtr();
            const result = underlying.rawAlloc(n, alignment, ret_addr) orelse
                return null;
            assert(alignment.check(@intFromPtr(result)));
            return result;
        }

        pub fn resize(
            ctx: *anyopaque,
            buf: []u8,
            alignment: Alignment,
            new_len: usize,
            ret_addr: usize,
        ) bool {
            const self: *Self = @ptrCast(@alignCast(ctx));
            assert(buf.len > 0);
            const underlying = self.getUnderlyingAllocatorPtr();
            return underlying.rawResize(buf, alignment, new_len, ret_addr);
        }

        pub fn remap(
            ctx: *anyopaque,
            buf: []u8,
            alignment: Alignment,
            new_len: usize,
            ret_addr: usize,
        ) ?[*]u8 {
            const self: *Self = @ptrCast(@alignCast(ctx));
            assert(buf.len > 0);
            const underlying = self.getUnderlyingAllocatorPtr();
            return underlying.rawRemap(buf, alignment, new_len, ret_addr);
        }

        pub fn free(
            ctx: *anyopaque,
            buf: []u8,
            alignment: Alignment,
            ret_addr: usize,
        ) void {
            const self: *Self = @ptrCast(@alignCast(ctx));
            assert(buf.len > 0);
            const underlying = self.getUnderlyingAllocatorPtr();
            underlying.rawFree(buf, alignment, ret_addr);
        }

        pub fn reset(self: *Self) void {
            self.underlying_allocator.reset();
        }
    };
}