GetUserProfileDirectoryW is now documented to always store the size

Author: RalfJung

library/std/src/sys/pal/windows/os.rs

@@ -202,8 +202,6 @@ fn home_dir_crt() -> Option<PathBuf> {
             |buf, mut sz| {
                 // GetUserProfileDirectoryW does not quite use the usual protocol for
                 // negotiating the buffer size, so we have to translate.
-                // FIXME(#141254): We rely on the *undocumented* property that this function will
-                // always set the size, not just on failure.
                 match c::GetUserProfileDirectoryW(
                     ptr::without_provenance_mut(CURRENT_PROCESS_TOKEN),
                     buf,

src/tools/miri/src/shims/windows/env.rs

@@ -230,16 +230,16 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         interp_ok(match directories::UserDirs::new() {
             Some(dirs) => {
                 let home = dirs.home_dir();
-                let size_avail = if this.ptr_is_null(size.ptr())? {
+                let size_avail = if this.ptr_is_null(buf)? {
                     0 // if the buf pointer is null, we can't write to it; `size` will be updated to the required length
                 } else {
                     this.read_scalar(&size)?.to_u32()?
                 };
                 // Of course we cannot use `windows_check_buffer_size` here since this uses
                 // a different method for dealing with a too-small buffer than the other functions...
                 let (success, len) = this.write_path_to_wide_str(home, buf, size_avail.into())?;
-                // The Windows docs just say that this is written on failure. But std
-                // seems to rely on it always being written.
+                // As per <https://github.com/MicrosoftDocs/sdk-api/pull/1810>, the size is always
+                // written, not just on failure.
                 this.write_scalar(Scalar::from_u32(len.try_into().unwrap()), &size)?;
                 if success {
                     Scalar::from_i32(1) // return TRUE