Bug: RegQueryValueExA/W is seemingly impossible to use correctly now

[monax3]

Which crate is this about?

windows

Crate version

0.40.0

Summary

RegQueryValueExA has the following signature:

pub unsafe fn RegQueryValueExA<'a, P0, P1>(hkey: P0, lpvaluename: P1, lpreserved: &mut u32, lptype: ::core::option::Option<&mut REG_VALUE_TYPE>, lpdata: *mut u8, lpcbdata: ::core::option::Option<&mut u32>) -> super::super::Foundation::WIN32_ERROR
where
    P0: ::std::convert::Into<HKEY>,
    P1: ::std::convert::Into<::windows::core::PCSTR>,

The documentation states:

lpReserved
This parameter is reserved and must be NULL.

This means it can't be called as references should never be NULL. &mut *std::ptr::null() does work for me but is technically UB).

I'm sure there's other cases like this since a lot of functions have this kind of argument but I couldn't find an existing issue.

Toolchain version/configuration

Default host: x86_64-pc-windows-msvc
rustup home: C:\Users\Mona.rustup

installed toolchains

stable-x86_64-pc-windows-msvc
nightly-x86_64-pc-windows-msvc (default)

Reproducible example

use std::ptr::null_mut;
use windows::core::{s, w, HSTRING, PCSTR};
use windows::Win32::Foundation::E_INVALIDARG;
use windows::Win32::System::Registry::{RegOpenKeyExA,RegOpenKeyExW, RegQueryValueExA, RegQueryValueExW, HKEY, HKEY_LOCAL_MACHINE, KEY_READ, RegCloseKey};

fn repro_a() {
    const KEY: PCSTR = s!(r"SOFTWARE\Microsoft\Windows\CurrentVersion\Setup");
    const VALUE: PCSTR = s!(r"BootDir");

    let mut hkey = HKEY::default();
    let mut len = 0;
    let mut zero = 0;
    unsafe {
        RegOpenKeyExA(HKEY_LOCAL_MACHINE, KEY,0, KEY_READ, &mut hkey).ok().unwrap();
        assert_eq!(RegQueryValueExA(hkey, VALUE, &mut zero, None, null_mut(), Some(&mut len)).ok(), Err(E_INVALIDARG.into()));
        assert!(RegQueryValueExA(hkey, VALUE, &mut *null_mut(), None, null_mut(), Some(&mut len)).ok().is_ok());
        RegCloseKey(hkey).ok().unwrap();
    }
}

fn repro_w() {
    const KEY: &HSTRING = w!(r"SOFTWARE\Microsoft\Windows\CurrentVersion\Setup");
    const VALUE: &HSTRING = w!(r"BootDir");

    let mut hkey = HKEY::default();
    let mut len = 0;
    let mut zero = 0;
    unsafe {
        RegOpenKeyExW(HKEY_LOCAL_MACHINE, KEY, 0, KEY_READ, &mut hkey).ok().unwrap();
        assert_eq!(RegQueryValueExW(hkey, VALUE, &mut zero, None, null_mut(), Some(&mut len)).ok(), Err(E_INVALIDARG.into()));
        assert!(RegQueryValueExW(hkey, VALUE, &mut *null_mut(), None, null_mut(), Some(&mut len)).ok().is_ok());
        RegCloseKey(hkey).ok().unwrap();
    }
}

fn main() {
    repro_a();
    repro_w();
}

Crate manifest

[package]
name = "regqueryvaluerepro"
version = "0.1.0"
edition = "2021"

[dependencies]
windows = { version = "0.40.0", features = ["Win32_Foundation", "Win32_System_Registry"] }

Expected behavior

lpreserved should accept either std::ptr::null() or None

Actual behavior

lpreserved only accepts a valid reference which is an invalid argument

Additional comments

No response

[kennykerr]

Thanks for reporting! This has now been fixed (#2036). I'll leave this open until I further apply Option to reserved parameters so that you can simply pass None instead of having to type std::ptr::null().