zig/doc/langref/test_errdefer_block.zig

const std = @import("std");
const Allocator = std.mem.Allocator;

const Foo = struct {
    data: u32,
};

fn tryToAllocateFoo(allocator: Allocator) !*Foo {
    return allocator.create(Foo);
}

fn deallocateFoo(allocator: Allocator, foo: *Foo) void {
    allocator.destroy(foo);
}

fn getFooData() !u32 {
    return 666;
}

fn createFoo(allocator: Allocator, param: i32) !*Foo {
    const foo = getFoo: {
        var foo = try tryToAllocateFoo(allocator);
        errdefer deallocateFoo(allocator, foo);

        foo.data = try getFooData();

        break :getFoo foo;
    };
    // This lasts for the rest of the function
    errdefer deallocateFoo(allocator, foo);

    // Error is now properly handled by errdefer
    if (param > 1337) return error.InvalidParam;

    return foo;
}

test "createFoo" {
    try std.testing.expectError(error.InvalidParam, createFoo(std.testing.allocator, 2468));
}

// test