Rust-analyzer deduces an incorrect struct layout, increasing stated size

[blockmath]

rust-analyzer version: rust-analyzer 1.99.0-nightly (73dc916 2026-08-01)

rustc version: rustc 1.99.0-nightly (73dc9167f 2026-08-01)

editor or extension: Debian 13, occurs on Kate (LSP)

relevant settings: default nightly

repository link (if public, optional): N/A

code snippet to reproduce:

use std::{mem::ManuallyDrop, ptr::NonNull};

const TREE_ORDER: usize = 7;
const TREE_MIN_KEYS: usize = 3;
const TREE_MAX_KEYS: usize = 6;

pub struct Tree<T> {
    root: Box<Node<T>>
}

union NodeChildren<T> {
    nodes: [ManuallyDrop<Box<Node<T>>>; TREE_ORDER],
    leaves: [ManuallyDrop<Box<Leaf<T>>>; TREE_ORDER]
}

#[repr(C)]
struct Node<T> {
    children: NodeChildren<T>,
    parent: Option<NonNull<Node<T>>>,
    /// NOTE: keys here are stored as relative,
    /// such that the first leaf under this node is index 0.
    /// This allows O(log N) insertion.
    keys: [usize; TREE_MAX_KEYS],
    num_keys: usize,
    depth: usize
} impl<T> Node<T> {
    fn insert_node(&mut self, node: Box<Node<T>>) {

    }
}

struct Leaf<T> {
    inner: Vec<T>
}

When compiled, the struct Node<T> is 128 bytes, but rust-analyzer claims it is 136 due to adding 8 bytes of padding between children and parent. The same occurs without #[repr(C)], except that the fields are reordered (so the padding is between children and keys).

[ChayimFriedman2]

My rust-analyzer reports 128 bytes. You likely have an outdated rust-analyzer. If you update to latest nightly, does it still fail?

[blockmath]

My rust-analyzer is the latest version, I verified by running rustup update.

[ChayimFriedman2]

2026-08-01 is not the latest nightly (and the latest nightly isn't the latest r-a, but I don't think that should impact this case).