[Bug c++/107781] strchrnul' was not declared in this scope; did you mean 'strchr'? For contracts for canadian compilation

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107781

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #4)
> If we don't want to introduce a configure check for strchrnul then this
> would work:
> 
> --- a/gcc/cp/contracts.cc
> +++ b/gcc/cp/contracts.cc
> @@ -210,8 +210,8 @@ lookup_concrete_semantic (const char *name)
>  static bool
>  role_name_equal (const char *role, const char *name)
>  {
> -  size_t role_len = strchrnul (role, ':') - role;
> -  size_t name_len = strchrnul (name, ':') - name;
> +  size_t role_len = strcspn (role, ":");
> +  size_t name_len = strcspn (name, ":");
>    if (role_len != name_len)
>      return false;
>    return strncmp (role, name, role_len) == 0;

Yes, though I bet strcspn is often slower, because it has to support many
reject characters, not just 2 (the one specified plus '\0').
Though, on glibc it won't be much slower, due to:
  if (__glibc_unlikely (reject[0] == '\0')
      || __glibc_unlikely (reject[1] == '\0'))
    return __strchrnul (str, reject [0]) - str;
done at the start of strcspn.